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Dioscoreales
Dioscoreales
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Dioscoreales
Temporal range: Mid Cretaceous – Recent 116–0 Ma
Dioscorea communis
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Dioscoreales
Mart.[1][2][3]
Type species
Dioscorea villosa
Families
Synonyms
  • Burmanniales Heintze
  • Nartheciales Reveal & Zomlefer
  • Taccales Dumortier
  • Tamales Dumortier
  • Dioscoreanae Reveal & Doweld
  • Burmanniidae Heintze

The Dioscoreales are an order of monocotyledonous flowering plants, organized under modern classification systems, such as the Angiosperm Phylogeny Group or the Angiosperm Phylogeny Web. Among monocot plants, Dioscoreales are grouped with the lilioid monocots, wherein they are a sister group to the Pandanales. In total, the order Dioscoreales comprises three families, 22 genera and about 850 species.

Dioscoreales contains the family Dioscoreaceae, which notably includes the yams (Dioscorea) and several other bulbous and tuberous plants, some of which are heavily cultivated as staple food sources in certain countries.

Certain species are found solely in arid climates (incl. parts of Southern Africa), and have adapted to this harsh environment as caudex-forming, perennial caudiciformes, including Dioscorea elephantipes, the "elephant's foot" or "elephant-foot yam".

Older systems tended to place all lilioid monocots with reticulate veined leaves (such as Smilacaceae and Stemonaceae together with Dioscoraceae) in Dioscoreales; as currently circumscribed by phylogenetic analysis, using combined morphology and molecular methods, Dioscreales now contains many reticulate-veined vines within the Dioscoraceae, as well as the myco-heterotrophic Burmanniaceae and the autotrophic Nartheciaceae.

Description

[edit]

Dioscoreales are vines or herbaceous forest floor plants. They may be achlorophyllous or saprophytic. Synapomorphies include tuberous roots, glandular hairs, seed coat characteristics and the presence of calcium oxalate crystals.[5] Other characteristics of the order include the presence of saponin steroids, annular vascular bundles that are found in both the stem and leaf. The leaves are often unsheathed at the base, have a distinctive petiole and reticulate veined lamina. Alternatively they may be small and scale-like with a sheathed base. The flowers are actinomorphic, and may be bisexual or dioecious, while the flowers or inflorescence bear glandular hairs. The perianth may be conspicuous or reduced and the style is short with well developed style branches. The tepals persist in the development of the fruit, which is a dry capsule or berry. In the seed, the endotegmen is tanniferous and the embryo short.[6]

All of the species except the genera placed in Nartheciaceae express simultaneous microsporogenesis. Plants in Nartheciaceae show successive microsporogenesis which is one of the traits indicating that the family is sister to all the other members included in the order.

Taxonomy

[edit]

Pre-Darwinian

[edit]

For the early history from Lindley (1853)[7] onwards, see Caddick et al. (2000) Table 1,[8] Caddick et al. (2002a) Table 1[5] and Table 2 in Bouman (1995).[9] The taxonomic classification of Dioscoreales has been complicated by the presence of a number of morphological features reminiscent of the dicotyledons, leading some authors to place the order as intermediate between the monocotyledons and the dicotyledons.[9]

Male Dioscorea batatas (D. polystachya) in Hooker's A General System of Botany 1873

While Lindley did not use the term "Dioscoreales", he placed the family Dioscoraceae together with four other families in what he referred to as an Alliance (the equivalent of the modern Order) called Dictyogens. He reflected the uncertainty as to the place of this Alliance by placing it as a class of its own between Endogens (monocots) and Exogens (dicots)[10] The botanical authority is given to von Martius (1835) by APG for his description of the family Dioscoreae or Ordo,[3] while other sources[11] cite Hooker (Dioscoreales Hook.f.) for his use of the term "Dioscorales" in 1873[12] with a single family, Dioscoreae.[13] However, in his more definitive work, the Genera plantara (1883), he simply placed Dioscoraceae in the Epigynae "Series".[14]

Post-Darwinian

[edit]

Although Charles Darwin's Origin of Species (1859) preceded Bentham and Hooker's publication, the latter project was commenced much earlier and George Bentham was initially sceptical of Darwinism.[15] The new phyletic approach changed the way that taxonomists considered plant classification, incorporating evolutionary information into their schemata, but this did little to further define the circumscription of Dioscoreaceae. The major works in the late nineteenth and early twentieth century employing this approach were in the German literature. Authors such as Eichler,[16] Engler[17] and Wettstein[18] placed this family in the Liliiflorae, a major subdivision of monocotyledons. it remained to Hutchinson (1926)[19] to resurrect the Dioscoreales to group Dioscoreaceae and related families together. Hutchinson's circumscription of Dioscoreales included three other families in addition to Dioscoreaceae, Stenomeridaceae, Trichopodaceae and Roxburghiaceae. Of these only Trichopodaceae was included in the Angiosperm Phylogeny Group (APG) classification (see below), but was subsumed into Dioscoraceae. Stenomeridaceae, as Stenomeris was also included in Dioscoreaceae as subfamily Stenomeridoideae, the remaining genera being grouped in subfamily Dioscoreoideae.[9] Roxburghiaceae on the other hand was segregated in the sister order Pandanales as Stemonaceae. Most taxonomists in the twentieth century (the exception was the 1981 Cronquist system which placed most such plants in order Liliales, subclass Liliidae, class Liliopsida=monocotyledons, division Magnoliophyta=angiosperms) recognised Dioscoreales as a distinct order, but demonstrated wide variations in its composition.[5][9]

Dahlgren, in the second version of his taxonomic classification (1982)[20] raised the Liliiflorae to a superorder and placed Dioscoreales as an order within it. In his system, Dioscoreales contained only three families, Dioscoreaceae, Stemonaceae (i.e. Hutchinson's Roxburghiaceae) and Trilliaceae. The latter two families had been treated as a separate order (Stemonales, or Roxburghiales) by other authors, such as Huber (1969).[21] The APG would later assign these to Pandanales and Liliales respectively. Dahlgren's construction of Dioscoreaceae included the Stenomeridaceae and Trichopodaceae, doubting these were distinct, and Croomiaceae in Stemonaceae. Furthermore, he expressed doubts about the order's homogeneity, especially Trilliaceae. The Dioscoreales at that time were marginally distinguishable from the Asparagales. In his examination of Huber's Stemonales, he found that the two constituent families had as close an affinity to Dioscoreaceae as to each other, and hence included them. He also considered closely related families and their relationship to Dioscoreales, such as the monogeneric Taccaceae, then in its own order, Taccales. Similar considerations were discussed with respect to two Asparagales families, Smilacaceae and Petermanniaceae.[20]

In Dahlgren's third and final version (1985)[22] that broader circumscription of Dioscoreales was created within the superorder Lilianae, subclass Liliidae (monocotyledons), class Magnoliopsida (angiosperms) and comprised the seven families Dioscoreaceae, Petermanniaceae, Smilacaceae, Stemonaceae, Taccaceae, Trichopodaceae and Trilliaceae. Thismiaceae has either been treated as a separate family closely related to Burmanniaceae or as a tribe (Thismieae) within a more broadly defined Burmanniaceae, forming a separate order, Burmanniales, in the Dahlgren system.[23] The related Nartheciaceae were treated as tribe Narthecieae within the Melanthiaceae in a third order, the Melanthiales, by Dahlgren.[22] Dahlgren considered the Dioscoreales to most strongly resemble the ancestral monocotyledons, and hence sharing "dicotyledonous" characteristics, making it the most central monocotyledon order.[9] Of these seven families, Bouman considered Dioscoreaceae, Trichopodaceae, Stemonaceae and Taccaceae to represent the "core" families of the order. However, that study also indicated both a clear delineation of the order from other orders particularly Asparagales, and a lack of homogeneity within the order.[9]

Molecular phylogenetics and the Angiosperm Phylogeny Group

[edit]

The increasing availability of molecular phylogenetics methods in addition to morphological characteristics in the 1990s led to major reconsiderations of the relationships within the monocotyledons.[24] In that large multi-institutional examination of the seed plants using the plastid gene rbcL the authors used Dahlgren's system as their basis, but followed Thorne (1992)[25] in altering the suffixes of the superorders from "-iflorae" to "-anae".[a] This demonstrated that the Lilianae comprised three lineages corresponding to Dahlgren's orders Dioscoreales, Liliales, and Asparagaless.

Under the Angiosperm Phylogeny Group system of 1998,[26] which took Dahlgren's system as a basis, the order was placed in the monocot clade and comprised the five families Burmanniaceae, Dioscoreaceae, Taccaceae, Thismiaceae and Trichopodaceae.

In APG II (2003),[27] a number of changes were made to Dioscoreales, as a result of an extensive study by Caddick and colleagues (2002),[5][28] using an analysis of three genes, rbcL, atpB and 18S rDNA, in addition to morphology. These studies resulted in a re-examination of the relationships between most of the genera within the order. Thismiaceae was shown to be a sister group to Burmanniaceae, and so was included in it. The monotypic families Taccaceae and Trichopodaceae were included in Dioscoreaceae, while Nartheciaceae could also be grouped within Dioscoreales. APG III (2009)[29] did not change this, so the order now comprises three families Burmanniaceae, Dioscoreaceae and Nartheciaceae.

Although further research on the deeper relationships within Dioscoreales continues,[30][31][23] the APG IV (2016) authors felt it was still premature to propose a restructuring of the order. Specifically these issues involve conflicting information as to the relationship between Thismia and Burmanniaceae,[32] and hence whether Thismiaceae should be subsumed in the latter, or reinstated.[1]

Phylogeny

[edit]

Molecular phylogenetics in Dioscoreales poses special problems due to the absence of plastid genes in mycoheterotrophs.[30] Dioscoreales is monophyletic and is placed as a sister order to Pandanales, as shown in Cladogram I.[32][1]

Cladogram I: The phylogenetic composition of the monocots.[1]
monocots

Evolution

[edit]

The data for the evolution of the order is collected from molecular analyses since there are no such fossils found. It is estimated that Dioscoreales and its sister clade Pandanales split up around 121 million years ago during Early Cretaceous when the stem group was formed. Then it took 3 to 6 million years for the crown group to differentiate in Mid Cretaceous.

Subdivision

[edit]

The three families of Dioscreales constitutes about 22 genera and about 849 species[33] making it one of the smaller monocot orders.[31] Of these, the largest group is Dioscorea (yams) with about 450 species. By contrast the second largest genus is Burmannia with about 60 species, and most have only one or two.[31]

Some authors,[23] preferring the original APG (1998)families, continue to treat Thismiaceae separately from Burmanniaceae and Taccaceae from Dioscoreaceae.[31] But in the 2015 study of Hertwerk and colleagues, seven genera representing all three families were examined with an eight gene dataset. Dioscoreales was monophyletic and three subclades were represented corresponding to the APG families. Dioscoreaceae and Burmanniaceae were in a sister group relationship.[32]

Cladogram II: Relationship of Dioscoreales families[32] (number of genera)[33]
Dioscoreales

Etymology

[edit]

Named after the type genus Dioscorea, which in turn was named by Linnaeus in 1753 to honour the Greek physician and botanist Dioscorides.[9]

Distribution and habitat

[edit]

Species from this order are distributed across all of the continents except Antarctica. They are mainly tropical or subtropical representatives, but some members of families Dioscoreaceae and Nartheciaceae are found in cooler regions of Europe and North America. Order Dioscoreales contains plants that are able to form an underground organ for reservation of nutritions as many other monocots. An exception is the family Burmanniaceae which is entirely myco-heterotrophic and contains species that lack photosynthetic abilities.

Ecology

[edit]
Narthecium ossifragum - bog asphodel

The three families included in order Dioscoreales also represent three different ecological groups of plants. Dioscoreaceae contains mainly vines (Dioscorea) and other crawling species (Epipetrum). Nartheciaceae on the other hand is a family composed of herbaceous plants with a rather lily-like appearance (Aletris) while Burmanniaceae is entirely myco-heterotrophic group.

Uses

[edit]

Many members of Dioscoreaceae produce tuberous starchy roots (yams) which form staple foods in tropical regions. They have also been the source of steroids for the pharmaceutical industry, including the production of oral contraceptives.

Notes

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References

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Bibliography

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Dioscoreales

View on Grokipedia
from Grokipedia
Dioscoreales is an order of monocotyledonous flowering plants recognized in the APG IV classification system (2016), encompassing three families—Burmanniaceae, Dioscoreaceae, and Nartheciaceae—with approximately 900 species distributed across 21 genera. These plants are predominantly herbaceous, featuring a mix of climbing vines, rhizomatous herbs, and forest-floor species, many of which exhibit inferior ovaries and diverse floral adaptations such as branched stigmas. While some lineages are autotrophic with net-veined leaves reminiscent of dicots, others, particularly in Burmanniaceae and Thismiaceae (sometimes treated separately), are mycoheterotrophic, lacking and relying on fungal symbionts for nutrition. The order displays a largely tropical distribution, with concentrations in humid forests of , , and the , though some taxa extend into temperate regions of , , and . Habit-wise, the dominant family Dioscoreaceae includes twining climbers like those in the genus , which produce starchy tubers or rhizomes for energy storage and regrowth, often with heart-shaped or lobed leaves and small, greenish flowers. In contrast, Nartheciaceae comprises bog-dwelling herbs with grass-like leaves, while Burmanniaceae features diminutive, non-photosynthetic plants with colorful bracts. Taxonomic debates persist, with molecular studies suggesting potential reinstatement of additional families like Taccaceae and Thismiaceae based on phylogenetic evidence; recent research has also proposed the new family Afrothismiaceae (2023), though APG IV maintains the current three-family circumscription pending further resolution. Economically, Dioscoreales holds significant value through the genus Dioscorea, known as yams, where about 10 species are cultivated as staple foods in tropical regions, providing high-starch tubers that are a key component of for millions, particularly in and the Pacific. These also yield steroidal used in pharmaceutical production, such as precursors for corticosteroids and oral contraceptives derived from species like Dioscorea floribunda. Ecologically, the order contributes to understories and habitats, with mycoheterotrophic members highlighting complex mycorrhizal interactions, though some invasive vines like air potato () pose management challenges in non-native areas.

Description

Morphology and Anatomy

Dioscoreales exhibit typical monocotyledonous features, including a single , parallel or reticulate venation in leaves, and a , though with notable variations across the order. Plants in this order are primarily herbaceous, often with underground storage organs adapted for accumulation, and display diverse growth habits ranging from climbing vines to geophytic herbs. In the dominant family Dioscoreaceae (including the genus Tacca, formerly recognized as Taccaceae), plants are typically twining climbers or lianas with annual stems that can reach lengths of 10-15 meters, supported by rhizomatous or tuberous underground organs, though species in Tacca are rosulate herbs with basal leaves, petiolate and simple to decompound-lobed, featuring reticulate venation, erect sheathing petioles, and root tubers or rhizomes for perennation and seasonal dormancy; stems in Tacca show secondary thickening, a rare feature among monocots in the order. Leaves are alternate, simple, and often cordate, with palmate primary venation and reticulate secondary venation, featuring conduplicate vernation and pulvinate petioles. Stems possess vascular bundles arranged in two rings, with phloem internal to the metaxylem, and nodes often showing xylem and phloem glomeruli; glandular hairs are common on vegetative parts. Roots are fibrous, sometimes thorn-bearing, and the tubers—such as those in Dioscorea species—serve as starch storage structures, with cultivated yams capable of weighing up to 50 kg. Burmanniaceae contrast sharply, comprising mostly herbaceous, geophytic or rhizomatous plants that are often mycoheterotrophic and non-photosynthetic, lacking chlorophyll and relying on fungal associations. Growth is erect or ascending, with stems featuring a single ring of vascular bundles; leaves are reduced to alternate, scale-like sheaths, sessile and entire-margined. Underground parts include thin to fleshy roots or root tubers for storage, with stomata frequently absent on leaves. Nartheciaceae consists of perennial herbs with slender, creeping and simple, glabrous stems. Leaves are mostly basal and linear to grass-like, equitant and overlapping along the rhizome, with cauline leaves reduced in number (3–6) and smaller; venation is parallel, and often accumulate aluminum. are fibrous, and the habit is geophytic, typically adapted to or environments.

Reproduction

Most species in the Dioscoreaceae family are dioecious, featuring separate plants with unisexual flowers, although some species exhibit ; in contrast, flowers in the Tacca lineage are bisexual. Flowers in the Burmanniaceae and Nartheciaceae families are typically bisexual and perfect. Flowers across Dioscoreales are generally small and inconspicuous, often greenish-white, arranged in spikes, racemes, or panicles, with six tepals in two whorls that are free or connate at the base. The ovary is inferior, typically three-carpellate with axile or parietal placentation, and nectar is produced by septal nectaries at the base of the ovary or on the tepals to attract pollinators. In Dioscorea species (yams), male flowers bear three to six stamens, while female flowers have three plicate carpels and a wet stigma; fruits are often three-lobed capsules containing winged seeds. In the Tacca lineage, flowers are medium-sized with a short perianth tube and adnate stamens, yielding baccate fruits or loculicidal capsules with ridged seeds. Burmanniaceae produce radially symmetric flowers with three stamens opposite the inner tepals, resulting in septicidally dehiscent capsules and dust-like seeds. Nartheciaceae flowers are arranged in terminal racemes or umbels, with free or basally connate tepals, three stamens, and a half-inferior ovary; fruits are loculicidal capsules with numerous small seeds. Seed dispersal occurs primarily via wind due to winged or lightweight structures in many genera, with ballistic mechanisms reported in some Dioscorea species where capsules dehisce explosively. Asexual reproduction is prevalent, particularly in cultivated Dioscorea species, through vegetative propagation using tubers, rhizomes, or aerial bulbils formed in leaf axils, which develop into new plants without sexual reproduction. This method dominates agricultural practices for yams, enabling rapid clonal propagation and bypassing seed-based limitations. Similar vegetative strategies occur via root tubers in the Tacca lineage and rhizomes in Nartheciaceae.

Taxonomy

Historical Classifications

In the 18th century, species of the genus Dioscorea L., the type genus of the order, were initially classified by within the broad family as part of the emerging recognition of monocotyledons in systems like his (1753). Early 19th-century botanists further refined this by elevating the group; Brown formally described the family Dioscoreaceae in , distinguishing it based on morphological traits such as twining stems and tuberous rhizomes, though it remained embedded within larger monocot assemblages. By the mid-19th century, classifications began according greater autonomy to the group. In Genera Plantarum (1862–1883), and proposed Ordo Dioscoreaceae, treating it as a distinct order within the monocots, emphasizing floral and vegetative characters like unisexual flowers and scandent habits that set it apart from core . This ordinal status was echoed and expanded in Adolf Engler and Karl Prantl's Die Natürlichen Pflanzenfamilien (1887–1899), where Dioscoreaceae received dedicated treatment as a family in , incorporating geographical patterns—such as distribution—and anatomical features like vessel elements in stems to justify its separation from other lilioid orders. The late 19th and 20th centuries saw transitional refinements driven by morphology and , with systems like those of Alfred Rendle () and Armen Takhtajan (1950s–1980s) variably allying Dioscoreaceae with or proposing interim orders based on shared traits like inferior ovaries and bulbous storage organs, setting the stage for era-specific developments. Post-2000 updates in the (APG) systems marked a pivotal shift; APG II (2003) and APG III (2009) integrated initial molecular evidence with traditional morphology to affirm Dioscoreales as a monophyletic order, encompassing Dioscoreaceae alongside Burmanniaceae and other allies, resolving prior ambiguities in lilioid relationships.

Pre-Darwinian Era

In the mid-18th century, classified the genus within the artificial outlined in (1753), placing it in the class Hexandria (six stamens) and order Monogynia (one pistil), alongside genera such as and Tamus due to shared morphological traits like berry fruits and climbing habits. This grouping reflected Linnaeus's emphasis on reproductive structures rather than natural affinities, associating Dioscorea with what would later be recognized as elements of Smilacaceae and early concepts. Early 19th-century botanical explorations advanced family-level delineations, with Robert Brown establishing in 1810 during his systematic account of Australian flora, distinguishing it from broader based on vegetative and reproductive features like tuberous roots and unisexual flowers. This separation highlighted the distinct climbing vines and starchy underground storage organs characteristic of species, marking a shift toward more natural classifications informed by geographic collections from expeditions such as Flinders' voyage. By the mid-19th century, further refinements elevated Dioscoreaceae toward ordinal status in various systems, integrating traits like prominent and into hierarchical frameworks. Regional of the early to mid-19th century often treated African and American Dioscorea taxa separately, reflecting limited transcontinental comparisons; for instance, West African species like D. rotundata were documented in exploratory accounts from colonial surveys, while American taxa such as D. trifida appeared in neotropical treatments, emphasizing local morphological variations in tuber shape and leaf arrangement without unifying ordinal contexts. These works, such as early volumes of Flora of Tropical precursors and South American enumerations, underscored the genus's pantropical distribution but highlighted geographic isolation in taxonomic descriptions. A key limitation in pre-Darwinian classifications was the lack of recognition for mycoheterotrophic nutrition in Burmanniaceae, another component later allied with Dioscoreales; this led to frequent misplacements near Orchidaceae based solely on superficial seed similarities and reduced leafy habits, overlooking underground fungal dependencies. Such groupings, evident in early 19th-century systems, prioritized visible morphology over physiological adaptations, resulting in inconsistent ordinal assignments for these achlorophyllous herbs.

Post-Darwinian Developments

Following Darwin's publication of in 1859, taxonomic s of Dioscoreales began integrating evolutionary principles, shifting from purely descriptive systems to those emphasizing phylogeny and shared derived traits. In 1926, John Hutchinson proposed a phylogenetic that resurrected the order Dioscoreales, grouping Dioscoreaceae with allied families based on key synapomorphies such as and the production of tubers or rhizomes, which he viewed as adaptations supporting independent ordinal status among monocots. By the mid-20th century, classifications by Armen Takhtajan and Arthur Cronquist (1960s–1980s) incorporated ultrastructural and anatomical evidence to position Dioscoreales. Takhtajan recognized it as a distinct order within superorder Lilianae, proximate to , highlighting advanced features like vessel elements in the —a rarity in monocots indicating evolutionary progression—and sieve tube plastids with specific inclusions that aligned it with lilialean lineages. In contrast, Cronquist subsumed most Dioscoreales under order in subclass Liliidae, prioritizing broader floral and similarities while downplaying some anatomical distinctions. Mid-20th century revisions expanded the order to include Taccaceae and Burmanniaceae, driven by morphological parallels such as petaloid tepals and inferior ovaries, which suggested common evolutionary origins and justified their alignment with Dioscoreaceae despite ecological differences like mycoheterotrophy in Burmanniaceae. The 1990s marked a transition to cladistic approaches using morphological data, as in analyses by Caddick et al., which employed character matrices of floral, anatomical, and vegetative traits to infer monophyletic groupings, directly informing the Angiosperm Phylogeny Group's initial framework and setting the stage for molecular integration. These efforts revealed Dioscoreales as a cohesive clade but noted unresolved polytomies. Recircumscription studies, such as the 2002 analysis, consolidated dioecious genera like Tamus, Testudinaria, and Rajania into an expanded Dioscorea based on morphological and molecular evidence, reducing the generic count while emphasizing the family's core lianescent habit; as of 2025, this circumscription remains standard with no major changes.

Molecular Phylogenetics and APG System

The advent of in the late revolutionized the classification of angiosperms, including the order Dioscoreales, by providing evidence for based on DNA sequence data rather than morphological traits alone. The (APG) I system, published in , recognized Dioscoreales as a distinct monophyletic order within the monocots, separating it from —a departure from earlier systems that had grouped these taxa together based on shared floral features. This reclassification was supported by analyses of the plastid gene rbcL, which demonstrated strong bootstrap support for Dioscoreales as a clade comprising families such as Burmanniaceae, Dioscoreaceae, and Taccaceae. Subsequent updates in the APG II (2003) and APG III (2009) systems confirmed and refined this placement through expanded datasets incorporating both plastid genes (rbcL, matK) and nuclear ribosomal markers, revealing Burmanniaceae as sister to a of Dioscoreaceae plus Taccaceae (with Taccaceae often treated as included within Dioscoreaceae in these schemes). These analyses, drawing from multi-gene phylogenies across hundreds of monocot taxa, achieved high resolution for ordinal relationships, with posterior probabilities exceeding 95% for the Dioscoreales in Bayesian frameworks. The molecular data highlighted the order's position within the broader monocot tree, underscoring its divergence from other lilioid orders. The APG IV update in 2016 maintained this core structure, affirming Dioscoreales' stable placement within the Lilianae clade—a higher-level monocot group supported by concatenated analyses of up to 17 genes across nuclear, , and mitochondrial genomes. Recent advances, including full genome sequencing, have further refined relationships among long-branch taxa in Dioscoreales, such as lineages, by mitigating artifacts from accelerated substitution rates in non-photosynthetic species. Key findings from these studies include the evolution of in Burmanniaceae, marked by independent losses of biosynthesis genes (e.g., chla and chlb) across tribes, correlating with shifts to fungal-dependent and genome reduction.

Current Subdivision

The order Dioscoreales is currently subdivided into three families under the (: Burmanniaceae, Dioscoreaceae (including Taccaceae), and Nartheciaceae. This classification reflects molecular phylogenetic evidence integrating the order's while distinguishing these lineages based on shared morphological and anatomical traits. Dioscoreaceae, the largest family, encompasses approximately 800–900 species across 4–9 genera, including the economically significant genus Dioscorea, which comprises over 600 species known as yams and features climbing vines with tubers used for food and worldwide. Diagnostic traits include twining stems, often dioecious flowers, and bulbils or tubers for , with species diversity concentrated in tropical regions. In a 2002 recircumscription, all dioecious genera (such as Tamus, Testudinaria, and Rajania) were sunk into Dioscorea based on molecular and morphological evidence, reducing the generic count while emphasizing the family's core lianescent . Burmanniaceae consists of about 100 in 8–10 genera, primarily mycoheterotrophic that lack and rely on fungal symbionts for nutrition. These exhibit non-green, scale-like leaves and small, often subterranean stems, with highest diversity in tropical forests where they inhabit shaded, humid understories. Nartheciaceae includes about 40 in 5 genera, such as Narthecium and Niphotidium, comprising rhizomatous typically found in acidic wetlands and bogs of temperate regions, with grass-like leaves, to orange flowers, and capsules as fruits. Overall, in Dioscoreales peaks in the , with Dioscoreaceae dominating in terms of both and ecological impact.

Etymology

Origin of the Name

The name of the order Dioscoreales derives from the genus Dioscorea, its , combined with the "-ales," which denotes an order in . The genus Dioscorea was established by in (1753), honoring the first-century CE Greek physician and pharmacologist Pedanius Dioscorides, author of , an influential encyclopedia documenting over 600 and their uses. The suffix "-ales" follows the plural form of the Latin adjectival ending "-alis," a convention for naming plant orders that became standardized in the as systematic classifications evolved, exemplified in works like Bentham and Hooker's Genera Plantarum (1862–1883). The order Dioscoreales encompasses three primary families: Dioscoreaceae, commonly referred to as the yam family; Burmanniaceae, known as the burmannia family and named after the Dutch Johannes Burman (1707–1779); and Nartheciaceae, designated the bog asphodel family, derived from the genus Narthecium, from the Greek narthēx (rod or ferula), alluding to the stiff stems of its plants. In Dioscoreaceae, the genus is widely recognized under the common name yams, which must be distinguished from sweet potatoes (Ipomoea batatas); true yams are monocots in the Dioscoreaceae, native primarily to and , whereas sweet potatoes are dicots in the family. Certain Dioscorea species, such as D. bulbifera, bear the vernacular name air potato owing to their production of bulbils on aerial stems, and this plant has become established as an in subtropical regions like the .

Phylogeny and Evolution

Phylogenetic Relationships

Dioscoreales occupies a position within the monocots, specifically as part of the Lilianae clade in the APG IV classification system, where it forms a to based on molecular phylogenetic analyses of multiple genes. This placement is supported by extensive datasets including and nuclear markers, which consistently resolve Dioscoreales and as the earliest diverging lineages within Lilianae, following the divergence of . Internally, the phylogeny of Dioscoreales is characterized by Nartheciaceae as the basal family, sister to a comprising Burmanniaceae and Dioscoreaceae (sensu lato, including Tacca), with Dioscoreaceae representing the most derived group; this topology is corroborated by analyses of genome sequences from representative taxa across the order. Recent phylogenomic studies using full genomes further reinforce this structure, highlighting the challenges posed by long-branch attraction in mycoheterotrophic lineages but confirming the of the major families. A representative of monocot relationships illustrates the divergence of monocots around 130 million years ago (MYA), with Dioscoreales branching early within the liliids approximately 124 MYA at the stem node, positioning it basal to the -Liliales clade. In this diagram, the monocot tree begins with as the outgroup, followed by a resolving into and liliids; within liliids, + Dioscoreales form a supported sister pair (bootstrap >90%), diverging before the rapid radiation of . Key synapomorphies defining Dioscoreales include the presence of laticifers in stems and other tissues in certain lineages, particularly within Dioscoreaceae, and the reduction or loss of specific sclerenchyma tissues in leaves compared to other liliids. These features, alongside molecular support from APG datasets, underscore the order's distinct evolutionary trajectory within monocots.

Evolutionary History

The order Dioscoreales emerged during the , approximately 130–100 million years ago (MYA), as part of the broader of monocotyledons following the initial diversification of angiosperms. This timing aligns with the establishment of early ecosystems, where the climbing habit in ancestral lineages likely evolved to facilitate access to the forest canopy, enhancing light capture and reducing competition from understory vegetation. Such adaptations positioned Dioscoreales as key components of tropical floras, with twining vines in families like Dioscoreaceae enabling vertical growth in dense habitats. Diversification within Dioscoreales accelerated during the period, after the Cretaceous-Paleogene (K-Pg) around 66 MYA, particularly in Dioscoreaceae, where the of tubers provided storage for nutrients and water, conferring resistance to periodic droughts in expanding tropical savannas and seasonal forests. In contrast, —a derived nutritional strategy involving dependence on fungal symbionts—arose independently in Burmanniaceae during the , approximately 75-100 MYA, allowing these lineages to exploit shaded, nutrient-poor understories without photosynthetic investment. These innovations contributed to the order's , with emerging in many species to promote and in spatially fragmented tropical environments. Recent phylogenetic analyses, including a 2025 study utilizing full genomes and site-heterogeneous models, have resolved longstanding issues of long-branch attraction artifacts in Dioscoreales phylogenies, particularly affecting mycoheterotrophic taxa with elevated substitution rates; these approaches confirm robust relationships by mitigating convergent signal distortions. Biogeographically, Dioscoreales exhibit Gondwanan origins in southern continents, with ancestral lineages tied to the Eocene connections via , followed by dispersals to the and that shaped their distribution.

Fossil Record

The fossil record of Dioscoreales is limited and primarily consists of macrofossils assigned to Dioscoreaceae (including Tacca), with no confirmed specimens predating the early Cretaceous and significant gaps due to misidentifications in earlier reports. A review of 20 previously described taxa found that only four—Dioscoroides lyelli, Dioscorea wilkinii, a Dioscorea sp. from Kenya, and Tacca buzekii—could be reliably attributed to the family based on morphological comparisons with extant species, underscoring the incomplete nature of the record. The earliest potential evidence comes from Cratolirion bognerianum, a fossil from the Crato Formation (ca. 113 Ma) in northeastern , which has been tentatively linked to Dioscoreales though its precise affinities remain uncertain. More definitive records begin in the Eocene, including leaves of eocenicus from early Eocene sediments (57–54 Ma) in the Bikaner district of northwestern , marking the first Asian occurrence of the and suggesting its presence in humid tropical forests during that period. In North America, well-preserved capsular fruits with three wings and epigynous stigmas from the early Eocene Fossil Butte Member of the Green River Formation in southwestern represent two new species, lindgrenii and D. shermanii, indicating the genus's establishment in subtropical Eocene ecosystems and supporting a possible North American origin. Later fossils include trifoliate leaflets of section Lasiophyton from late volcaniclastic sediments (ca. 27.23 Ma) in northwestern , providing the earliest direct evidence for the genus in . For Tacca (in Dioscoreaceae), the oldest confirmed remains are seeds from the Eocene-Oligocene boundary (ca. 33.9 Ma) in , followed by leaves from early Miocene deposits (ca. 21.73 Ma) in the same Ethiopian region, consistent with moist tropical habitats. The family Burmanniaceae has no direct fossil record before the , with its deep antiquity—estimated to the (ca. 116 Ma)—inferred mainly from analyses rather than paleontological evidence. Overall, the scarcity of fossils, particularly for or underground structures like tubers, limits insights into early diversification, though the Eocene records imply a rapid post-Cretaceous radiation across and .

Distribution and Habitat

Global Distribution

The order Dioscoreales exhibits a predominantly distribution, with occurring across tropical and subtropical regions worldwide, excluding . Comprising approximately 850 accepted across , the order is characterized by its concentration in humid tropical environments, though some taxa extend into warmer temperate zones. The largest family, Dioscoreaceae, includes about 650 , primarily in the genus (over 600 ), and is distributed across , , and the , with significant diversity in each continent. In , more than 140 are native, particularly in West and Central regions, where they form a key component of forest and savanna flora. Asian and American distributions are also extensive, with adapted to diverse tropical ecosystems from to the . The genus Tacca (10–13 , formerly Taccaceae) is centered in the region, from through northern and Pacific islands to parts of tropical . Burmanniaceae, with around 100 in about 10 genera, is largely confined to the tropics, spanning , , and the , often in shaded, moist understories. Nartheciaceae, comprising about 35 in five genera, has a northern temperate distribution, occurring in eastern , , and . Centers of diversity are pronounced in for edible yams (Dioscorea spp.), where species like D. rotundata and D. cayenensis originated and remain vital to , supporting over 96% of global yam production. stands out for mycoheterotrophic taxa, particularly in Burmanniaceae and certain Dioscorea lineages, with high endemism in humid forests of , , and . Limited temperate extensions occur, such as Dioscorea villosa in the and D. transversa in eastern , though these are outliers amid the order's tropical core; Nartheciaceae represents the primary temperate component. Many , including D. alata, have been introduced globally through cultivation, now naturalized in over 50 tropical countries beyond their native ranges.

Preferred Habitats

Members of the Dioscoreales order predominantly inhabit tropical and subtropical regions, favoring humid environments such as lowland , margins, open woodlands, and grasslands. These thrive in areas with well-drained, fertile loamy soils that support their tuberous or rhizomatous growth forms, allowing for and uptake in variable conditions. The dominant family, Dioscoreaceae, includes climbing species like yams that prefer shaded understories of tropical rainforests and savannas, as well as disturbed edges where light penetration aids growth; these habitats provide the for twining stems while tubers develop in deeper soil layers. In seasonally dry areas, species exhibit in their aerial parts during , relying on tubers to survive until rains resume, typically in climates with average temperatures of 20–30°C and annual rainfall exceeding 1,500 mm. They occur from to altitudes of about 2,000–2,500 m, particularly on well-drained slopes in wet tropical lowlands and montane forests. The genus Tacca inhabits humid lowland forests, monsoon-influenced woodlands, and shady understories in tropical regions, including forest margins and grasslands with high moisture retention; these acaulescent herbs prefer well-drained soils in areas of frequent rainfall, with temperatures in the warm tropical range. Burmanniaceae species, often mycoheterotrophic and reliant on mycorrhizal fungi for , are adapted to the shaded, organic-rich floors of humid tropical rainforests, wet thickets, and grasslands, where fungal associations facilitate nutrient acquisition in low-light conditions. These favor moist, shaded microhabitats with consistent , occurring from low elevations to up to 3,000 m in montane . Nartheciaceae species are herbaceous found in wet, boggy habitats such as swamps, marshes, meadows, and edges, primarily in northern temperate regions. They prefer acidic, peaty soils with high moisture and occur from low elevations to montane areas, often in open or partially shaded conditions.

Ecology

Growth and Life Cycles

Members of the order Dioscoreales exhibit diverse growth habits, predominantly as perennial herbs or twining that perennate via underground tubers or rhizomes, enabling seasonal during unfavorable conditions. In the dominant family Dioscoreaceae, plants emerge from tubers at the onset of favorable growing seasons, such as the rainy period in tropical regions, undergoing an active growth phase characterized by rapid vine extension and production. This cycle typically spans 6-12 months for many yam (Dioscorea spp.), culminating in tuber maturation and of aboveground parts, followed by a period of 30-150 days in harvested tubers. Vines can achieve remarkable growth rates, reaching up to 25 cm per day and lengths of 51 m within a single season. Germination occurs from seeds or tuber pieces, with seedlings exhibiting rapid in the first year to establish support on or structures. Flowering generally follows establishment, often after 1-3 years in wild populations, though timing varies with and environmental cues. Wild vines typically have lifespans of 5-20 years, while cultivated plants can persist longer through repeated asexual via tubers, which dominates agricultural practices and allows for perennial-like continuity. Tubers play a key morphological role in storage and regrowth, renewed annually or persisting perennially. In Nartheciaceae, species are rhizomatous herbs adapted to habitats like bogs and wet meadows, with grass-like leaves and seasonal flowering in summer. Variations exist across families; while annuals are rare in Dioscoreales, some members of Burmanniaceae display short-lived habits as small, mycotrophic herbs that complete their life cycle in one , though perennial forms with rhizomes or tubers also occur. These mycoheterotrophic often lack and rely on fungal associations for , contrasting with the photosynthetic, tuber-dependent strategy of Dioscoreaceae.

Pollination and Seed Dispersal

In the Dioscoreaceae, the dominant family of Dioscoreales, is primarily entomophilous, with small, inconspicuous flowers attracting a diverse array of including (Thysanoptera), biting midges (), beetles (Coleoptera), flies (Diptera), and bees (). These species are predominantly dioecious, with separate , which enforces and reduces self-fertilization, though asynchronous flowering between sexes can limit seed set in sparse or isolated populations. Many exhibit nocturnal , with pale flowers opening at dusk to facilitate by nocturnal , enhancing cross-pollination efficiency in tropical understories. In contrast, species in the genus Tacca (formerly Taccaceae, now included in Dioscoreaceae) feature flowers with dark coloration and carrion-like odors that mimic fungal or decaying matter, attracting female biting midges such as Forcipomyia and species through sapromyiophily. Despite these traits suggesting specialized , autonomous predominates, with anthers dehiscing before to deposit directly on receptive stigmas, resulting in high selfing rates (up to 94%) and low . Mycoheterotrophic taxa in Burmanniaceae (including Thismiaceae sensu lato), such as Burmannia and Thismia, display reduced floral structures adapted for or visitation by minute insects like () and phorid flies (), which may be drawn to fungal-associated scents, though direct fungal mediation in transfer remains unconfirmed. In Nartheciaceae, flowers are entomophilous, primarily pollinated by bees and flies, with septal nectaries attracting visitors for cross-pollination in habitats. Seed dispersal in Dioscoreales varies by fruit type and habitat. In Dioscoreaceae, dehiscent capsules release winged primarily via anemochory ( dispersal), with explosive dehiscence or aiding short-distance spread in some species; however, indehiscent berries in taxa like elephantipes facilitate zoochory, where birds and mammals consume the fruit and excrete viable . Species in the genus Tacca produce ridged, corky from loculicidal capsules, likely dispersed by or ballistic mechanisms, while Burmanniaceae (including Thismiaceae sensu lato) generate dust-like with filiform appendages, enabling splash-cup dispersal during rain events or limited transport in humid forest floors. In Nartheciaceae, dehiscent capsules release small dispersed by in open environments. These strategies align with the order's tropical to subtropical distributions, promoting in fragmented habitats while minimizing dependency on specific dispersers.

Biotic Interactions

Members of the order Dioscoreales engage in various biotic interactions that influence their survival, growth, and distribution. These include symbiotic associations with fungi, antagonistic relationships with herbivores and pathogens, and mutualistic partnerships with . Such interactions are particularly pronounced in the families Dioscoreaceae and Burmanniaceae, where they play critical roles in acquisition and defense. Mycorrhizal associations are essential for uptake in Dioscoreales, especially in mycoheterotrophic lineages. In Burmanniaceae, like those in the genus Burmannia form associations with arbuscular mycorrhizal fungi (AMF), relying on them for up to 100% of their carbon and s as holomycotheterotrophs. These fungi, often from the , facilitate carbon transfer from autotrophic host plants, enabling the survival of achlorophyllous Burmanniaceae in -poor forest understories. In contrast, Dioscoreaceae exhibit partial mycorrhizal colonization in , with AMF enhancing phosphorus uptake and overall growth in tuberous like yams ( spp.); inoculation studies show colonization rates of 63-90%, leading to increased tuber weight and yield under stress conditions. Nartheciaceae also form arbuscular mycorrhizal associations of the Paris type, aiding acquisition in acidic, -poor soils. Herbivory poses significant threats to Dioscoreales, targeting both tubers and foliage. Tubers of Dioscorea species are frequently consumed by rodents and wild pigs (Sus scrofa), which can destroy crops in field settings, leading to substantial yield losses in agricultural areas. Leaves and stems are attacked by diverse insects, including over 70 species such as yam beetles (Heteroligus spp.), leaf miners, and mealybugs, which defoliate vines and reduce photosynthetic capacity. Chemical defenses, including steroidal sapogenins like diosgenin, deter herbivores by exhibiting toxicity and bitterness; these compounds accumulate in tubers and leaves, providing a key anti-herbivory mechanism across Dioscoreaceae. Pathogenic interactions further challenge Dioscoreales, with fungal and viral agents causing widespread damage. Fungal blights, notably anthracnose caused by Colletotrichum species (e.g., C. gloeosporioides or C. alatae), infect leaves, stems, and tubers of yams, resulting in necrotic lesions and yield reductions of 50-90% in West African production regions. Viral pathogens, such as yam mosaic virus (Potyvirus) and Dioscorea bacilliform viruses, induce mosaic patterns, stunting, and necrosis on foliage, often co-occurring and exacerbating disease complexity in Dioscorea crops. Additionally, invasive species like air potato (Dioscorea bulbifera) in Florida disrupt native ecosystems by outcompeting local flora through rapid vegetative spread, though its own biotic interactions include susceptibility to similar pathogens. Mutualistic relationships, such as protection on vines, provide biotic defense in some Dioscoreaceae. Species like Dioscorea praehensilis produce extrafloral nectaries that attract s (e.g., Oecophylla spp.), which patrol vines and reduce herbivory by preying on or deterring insect attackers; this opportunistic interaction can decrease leaf damage by up to 50% during vulnerable growth phases. These associations highlight the role of indirect defenses in enhancing vine survival in tropical habitats.

Uses

Economic and Food Uses

Yams ( spp.), particularly species within the , are a cornerstone staple crop in tropical regions, especially and parts of , where they provide essential carbohydrates for over 60 million people. Global production reached 87.64 million tonnes in 2023, with accounting for over 96% of output, led by countries like , , and Côte d'Ivoire. These tubers are prized for their high carbohydrate content, comprising 70-80% of dry weight primarily as , along with notable levels of vitamins such as and , making them a key energy source in diets. Cultivation of yams focuses on around 12 major species, including the white yam (D. rotundata), yellow yam (D. cayenensis), and water yam (D. alata), which are propagated vegetatively using tuber setts—sections of mature tubers planted directly in mounds or ridges. These vines thrive in well-drained, fertile soils and require staking for support, with harvesting occurring 8-11 months after planting. Under improved management practices, yields typically range from 10 to 30 tonnes per hectare, though global averages hover around 9 tonnes per hectare due to challenges like pests and low . The edible tubers, which store the plant's energy reserves, form the basis of this agricultural system. In processing, yams are versatile: fresh tubers are often boiled and eaten whole or sliced, but in , they are commonly pounded into a smooth, elastic dough called , served with soups and stews. Fermentation methods, such as soaking sliced tubers to produce products like amala or , enhance flavor and while improving digestibility. Nutritionally, yams offer low protein (around 2% on a fresh weight basis) but high (4-5% fresh weight), contributing to their role as a satiating, low-fat . Economically, the yam sector generates approximately $48 billion in annual production value globally as of 2023, with Nigeria alone contributing approximately $25 billion from 61 million tonnes in 2022, underscoring its critical role in West African subsistence farming and rural livelihoods. While remains modest at around $243 million in imports, yams support and local markets for millions of smallholder farmers.

Medicinal and Pharmacological Uses

Diosgenin, a steroidal sapogenin extracted from the tubers of various species such as and Dioscorea composita, serves as a key precursor in the industrial synthesis of pharmaceutically important steroids, including progesterone and . This compound undergoes the Marker degradation process to yield progesterone, which was pivotal in the development of oral contraceptives starting in the . By the 1960s, yam-derived diosgenin had become the primary source for synthesizing hormones used in pills, enabling mass production and widespread availability of these medications. Additionally, diosgenin-based synthesis facilitated the economical production of , revolutionizing treatments for inflammatory conditions like . In systems, Dioscorea species have been employed for their properties, particularly in and Chinese herbal practices. Tubers of species like are used to manage by lowering blood glucose levels, as documented in Indian and Chinese pharmacopeias. Leaves and tubers also find application in ; for instance, extracts from D. bulbifera promote tissue repair and exhibit effects against cytokines such as TNF-α and IL-6. In Ayurvedic traditions, tubers are applied topically to treat ulcers and abscesses due to their content, which supports cell proliferation. Modern pharmacological research highlights the potential of species, with D. alata showing notable activity attributed to anthocyanins and polyphenolic compounds. These bioactive elements neutralize free radicals, contributing to reduction in cellular models. Studies on purified anthocyanins from D. alata tubers demonstrate enhanced capacity, including radical scavenging and improved activities like in animal models. Such properties suggest therapeutic roles in preventing chronic diseases linked to oxidative damage, though clinical trials remain limited. Despite these benefits, Dioscoreales plants contain crystals () that pose risks, causing oral and dermal , , and acrid taste upon . Wild yams like are particularly hazardous due to high concentrations and , necessitating detoxification through processing methods such as boiling or fermentation to render them safe for medicinal use.

Ornamental and Other Uses

Several species within the Dioscoreales order are cultivated for ornamental purposes due to their distinctive foliage and floral structures. , commonly known as the bat plant, is prized in gardens and as a potted for its exotic, bat-like inflorescences featuring dark purple-black bracts and long, whisker-like filaments, which add a dramatic tropical aesthetic to shaded landscapes. Certain species, such as (Chinese yam), are grown ornamentally for their vigorous climbing vines and heart-shaped leaves, providing lush green coverage in temperate and subtropical gardens, though some introductions have become invasive. Beyond aesthetics, Dioscoreales have industrial applications, particularly through starch extraction from Dioscorea tubers. Yam starch is utilized in the production of textiles, adhesives, and due to its favorable , gelling properties, and binding capabilities, serving as a renewable alternative in processes. While less prominent, fibers derived from Dioscorea stems have been employed in traditional crafts for and cordage in certain indigenous contexts. Culturally, yams from Dioscorea species hold significant ritual importance in various societies. In , the New Yam Festival (Iri Ji) among the celebrates the harvest with ceremonies that honor ancestors and ensure community prosperity, underscoring yams' sacred status as symbols of abundance and fertility. Additionally, tubers show promise for bioenergy production, with species like sansibarensis yielding high carbohydrate content suitable for bioethanol conversion, potentially supporting sustainable fuel alternatives in tropical regions. Minor uses include animal , where by-products such as peels and vines serve as nutritious supplements in and feeds, enhancing growth without compromising performance. In systems, the climbing habit of vines contributes to by providing ground cover that mitigates on slopes, integrating well with other crops for sustainable .

Conservation

Threats and Challenges

Dioscoreales species, particularly those in the Dioscoreaceae family, face significant threats from loss primarily driven by and in tropical regions. Deforestation for timber, , and conversion to farmland has fragmented and reduced suitable habitats, affecting wild populations of yams ( spp.) and their relatives. In regions like , , and , these activities have led to the loss of forest understories where many Dioscoreales thrive, with ironically threatening wild relatives of cultivated yams through land clearance for crop production. For instance, in southern , species such as Dioscorea hirtiflora are impacted by rates exceeding sustainable levels, contributing to population declines. Globally, degradation is a primary driver of threat for species, with 32% of the 81 assessed species classified as threatened on the as of 2021. Overharvesting poses another major risk to Dioscoreales, especially wild yams harvested for food and . Unsustainable collection of tubers from natural populations has depleted stocks in areas like and , where species such as strydomiana are critically endangered due to medicinal demand, often involving complete uprooting that prevents regeneration. In northwestern , uncontrolled harvesting for supplementary nutrition has degraded dry forest ecosystems by targeting high densities of wild yams, exacerbating and . Additionally, invasive species within the order, notably (air potato), displace native Dioscoreales by forming dense vegetative mats that smother understory plants and alter community structures in tropical forests of and beyond, reducing availability for indigenous species. Climate change further compounds these pressures on Dioscoreales through increased droughts and shifting precipitation patterns that impair tuber viability and overall plant health. In West Africa's savanna zones, projected rises in temperature and erratic rainfall are expected to reduce yam yields by stressing tuber development, with droughts coinciding with critical growth phases leading to lower viability and higher failure rates in propagation. This is particularly acute for tuber-dependent species reliant on consistent moisture for dormancy and sprouting. Rising temperatures and altered climates also facilitate the spread of pests and diseases; for example, the yam mosaic virus (YMV), transmitted by aphids, has become more prevalent in affected regions, reducing tuber size and quality in both wild and cultivated populations, while anthracnose (Colletotrichum gloeosporioides) infects leaves and stems across yam-growing areas. According to the , 32% of the 81 assessed are threatened with as of , reflecting cumulative impacts from these factors. Note that IUCN assessments remain incomplete, covering only a fraction of the approximately 600 known . The , comprising mycoheterotrophic with narrow specificity in shaded floors, is particularly vulnerable, with several taxa such as Biermannia jainiana classified as Critically Endangered and Burmannia capitata highly threatened by and succession in tropical understories. These assessments underscore the order's overall fragility, with hotspots in biodiversity-rich like showing up to 38% of wild yam at risk.

Conservation Strategies

Conservation efforts for Dioscoreales emphasize a combination of protection, ex situ preservation, and targeted research to safeguard the of species, particularly in hotspots like the Amazon and . Protected areas play a crucial role in conserving wild relatives, with reserves such as the Trinational in the encompassing occurrences of taxa and supporting overall forest that includes yam diversity. In the Amazon, national parks and indigenous territories protect habitats from deforestation, though coverage remains limited at approximately 4.87% of known occurrences globally. Additionally, the () regulates trade in medicinal species like , listed in Appendix II to prevent overexploitation. Cultivation programs focus on reducing pressure on wild populations through sustainable propagation techniques. In vitro methods, such as slow-growth protocols at 25°C with biannual subculturing, enable the maintenance of virus-free and minimize wild harvesting. Gene banks are central to these efforts, with the (IITA) in holding 5,839 accessions of spp., representing 42.6% of the global ex situ collection and including key species like D. alata and D. rotundata. These collections support breeding and distribution, with safety duplication in sites like to enhance resilience against loss. Ongoing research addresses emerging challenges, including the development of climate-resilient varieties through 2025 initiatives by organizations like IITA and partners in . These programs have released varieties yielding 20–30 tons per under and low-fertility conditions, tested in , , and Côte d’Ivoire to sustain production amid environmental stresses. Restoration planting in degraded habitats, such as participatory schemes in Madagascar's Ankarafantsika , involves cultivating 25 wild species across 60 communities to restore ecosystems and bolster local livelihoods. Policy frameworks in major yam-producing countries integrate conservation into agricultural planning. Nigeria's National Root and Tuber Expansion Programme promotes use and on-farm conservation, while Benin's ennoblement practices and Ghana's improvement efforts align with regional strategies to protect wild relatives. has developed a national strategy for wild yams, complementing cultivated varieties through community-based management. Kew's (POWO) provides updated threat assessments as of 2025, informing global prioritization by integrating data for species like D. irodensis.

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