Rhododendron arboreum, the tree rhododendron, is an evergreen shrub or small tree with a showy display of bright red flowers. It is found in Bhutan, China, India, Myanmar, Nepal, Sri Lanka, Pakistan and Thailand. It is the national flower of Nepal.

Its specific epithet means "tending to be woody or growing in a tree-like form".^{[citation needed]} It has been recorded as reaching heights of 20 m (66 ft), though it is more usually 12 m (39 ft) tall and broad. This plant holds the Guinness Record for the World's Largest Rhododendron. The tree discovered in 1993 at Mount Japfü in the Kohima District of Nagaland, India, holds the Guinness Record for the tallest Rhododendron at 20 m (65 ft). In sharp contrast to this, the New Guinean epiphytic species Rhododendron caespitosum never exceeds 4 in (10 cm) in height.

In early- and mid-spring, trusses of 15–20 bell-shaped flowers, 5 cm (2 in) wide and 3–5 cm (1–2 in) long are produced in red, pink or white. They have black nectar pouches and black spots inside.

Rhododendron arboreum is found in the Pakistan, India, Nepal, Myanmar, Sri Lanka, the Himalayas, Northeast India, and Tibet. It was introduced in Madeira.

It is the national flower of Nepal. In India it is the state tree of Uttarakhand and state flower of Nagaland. It is the provincial flower of Sri Lanka's Central Province.

Rhododendron arboreum prefers moist but well-drained, leafy, humus-rich, acid pH soil, in dappled shade. It has broad, dark green leaves, 7–19 cm (3–7.5 in) long, with a silvery, fawn or brown hairy coating beneath.

This plant is suitable for woodland gardens.

Shelter is imperative to prevent wind damage to leaves.