菱形叶杜鹃 ling xing ye du juan

Shrubs, often epiphytic, 2–3 m tall; old branches gray; young shoots densely brown-scaly. Petiole short, 5–12 mm, densely brown-scaly; hispid on both surfaces when young, glabrescent; leaf blade rhomboidal or rhomboidal-lanceolate, 5–8.5 × 2–3 cm; base cuneate; apex acuminate; abaxial surface brown when dry, scales less than 1 × their own diameter apart, large, unequal, brownish red; adaxial surface glabrous; midrib raised abaxially, concave adaxially; lateral veins thin, inconspicuous on both surfaces. Flowers not seen, infructescence umbellate, 3- or 4-fruited. Pedicel stout, 0.6–1 cm, densely brown-scaly; fruiting calyx margin wavy, ciliate, ca. 2 mm, persistent; style persistent, basal 1/3 with scales. Capsule cylindric or ovoid-cylindric, 6-lobed, 12–20 × 8–12 mm, densely brown-scaly.

Broad-leaved forests, sometimes epiphytic on trees in dense forests; 1800–1900 m. Yunnan.

The leaf shape of Rhododendron rhombifolium is close to that of the sympatric R. taronense, but the clearly ciliate calyx of the former distinguishes the two species. Flowering material is required before the true affinities of R. rhombifolium can be ascertained, as the type specimen is in fruit. The label on the isotype at E (“Salwin-Kiukiang Divide, Muchielung, 1800 m, 8 Oct. 1938, T. T. Yü 20581”) is somewhat at variance with the citation in the protologue (“Gongshan, ad truncos in sylvis densis, alt. 1800 m, 8 Oct. 1937, T. T. Yü 20581”).