A botanical specimen, also called a plant specimen, is a biological specimen of a plant (or part of a plant) used for scientific purposes. Preserved collections of algae, fungi, slime molds, and other organisms traditionally studied by botanists are also considered to be botanical specimens. Plant specimens are usually preserved by drying and pressing using a basic technique that is more than 500 years old. Other examples of preserved specimens include loose seeds, wood sections, and microscope slides. A facility devoted to the curation of a collection of botanical specimens is known as a herbarium.

A person who gathers botanical specimens is called a botanical collector (or plant collector). Plant collecting is an essential botanical activity with a very long history. Some plant science journals require botanical specimens as a condition for publication of articles.

The terms herbarium specimen, voucher specimen, and type specimen refer to botanical specimens with a particular use or quality.

The term herbarium specimen emphasizes the fact that a botanical specimen has been deposited in a herbarium, an institution specifically designed to facilitate the sharing of preserved specimens. A herbarium specimen is usually dried, pressed, and mounted on paper but other methods of preservation are used as well.

A voucher specimen is a herbarium specimen intended to support a research project or a field survey. Among other things, vouchers help to protect against errors in plant identification.

To be useful, a botanical specimen must be identified as a member of some taxonomic group at a given rank. Whether or not the collector identifies the specimen initially, other botanists are free to make a determination at any time. If a botanist believes that the specimen represents a new taxon, the botanist may publish a new name and description, in which case she becomes the author of the name and the specimen becomes the type of the taxon. Every plant species is associated with a type, either a botanical specimen or a botanical illustration. In either case the type serves as the basis for the botanical name of the taxon.

In 1841, the American botanist Ferdinand Rugel collected two specimens, one in North Carolina and the other in Georgia. The English botanist Alfred Barton Rendle published new names and descriptions for both specimens in 1901. Rendle applied the names Trillium rugelii and Trillium affine, respectively. In the 1980s, the American botanist Thomas Stewart Patrick determined that both specimens represented a single species.

In the previous scenario, Rugel is the collector, Rendle is the author, and Patrick is the determiner. Obviously Rendle and Patrick disagree but anyone can inspect the specimens, read the descriptions, and formulate an opinion: either there are two distinct species, Trillium rugelii Rendle and Trillium affine Rendle, or the name Trillium affine Rendle is a synonym for Trillium rugelii Rendle. As of June 2023^[update], botanists favor a single species concept. Future opinion might change but in any case, Trillium affine Rendle is still a validly named and described species, and its type is the specimen collected by Rugel in Georgia in 1841.