11. Ledum Linnaeus, Sp. Pl. 1: 391. 1753.
杜香属 du xiang shu
Fang Ruizheng (方瑞征 Fang Rhui-cheng); David F. Chamberlain
Shrubs evergreen, small, multibranched, with fragrant resin. Leaves shortly petiolate; leaf blade linear, linear-lanceolate, or narrowly oblong, leathery, abaxially with white and/or rusty brown-pilose or woolly indumentum, margin entire, recurved. Inflorescences terminal, racemose, many-flowered; bracts present at peduncle base, dry, membranous, soon deciduous; bractlets absent. Calyx small, 5-lobed, persistent. Corolla white, divided to base; lobes imbricate in bud. Stamens (5–)8–10, protruding beyond corolla; filaments linear; anthers small, abaxially connected, globose, without appendages. Flower disk 8–10-lobed. Ovary globose, 5-locular, lepidote. Style linear; stigma obtuse, 5-lobed. Capsule ellipsoid or cylindric, opening from base. Seeds tiny.
Three or four species: circumboreal in temperate and cold-temperate regions; one species in China.
DNA sequencing has shown that this genus should be included within Rhododendron subg. Rhododendron, as R. subsect. Ledum (Linnaeus) Kron & Judd (Syst. Bot. 15: 67. 1990). It has affinities with R. subsect. Micrantha.
Ledum subulatum (Nakai) A. P. Khokhrjakov & Mazurenko (in Kharkevich, Sosud. Rast. Sovetsk. Dal’nego Vostoka 5: 125. 1991; L. palustre var. subulatum Nakai, Bot. Mag (Tokyo) 31: 103. 1917; Rhododendron subulatum (Nakai) Harmaja) was described from N Korea and has been recorded also from Japan and (mainly) Russia. Harmaja (Ann. Bot. Fenn. 39: 183–184. 2002) also cited “NE China,” but without locality. The taxon is said to have a subulate leaf blade, 10–36 × 1–3 mm, with a revolute margin and reddish brown, floccose hairs abaxially. From this description it is unclear how distinct L. subulatum is from L. palustre.