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139. Dendrobium Swartz, Nova Acta Regiae Soc. Sci. Upsal., ser. 2. 6: 82. 1799.

石斛属 shi hu shu

Authors: Guanghua Zhu, Zhanhe Ji, Jeffrey J. Wood & Howard P. Wood

Herbs epiphytic, lithophytic, or less often terrestrial, polymorphic, deciduous or evergreen. Stems either: 1) rhizomatous, 2) erect and many noded, 3) erect and 1-noded or several noded from a many-noded rhizome, or 4) without a rhizome, new stems of many nodes arising from base of old ones; 1 or 2(-500) cm, tough or fleshy, 1 to several internodes swollen at or near base or along entire length to form canelike pseudobulbs, ± covered with sheathing leaf bases and cataphylls, often turning yellow when dried. Leaves 1 to many, alternate, apical or distichous along stem, linear, lanceolate, oblong, or ovate, sometimes subterete or terete, papery to rigid and leathery, sometimes with black or brown trichomes especially on sheath, base articulate and often with clasping sheaths, apex usually 2-lobed or emarginate. Inflorescences lateral, generally distal, in some sections pseudoterminal, 1- to many flowered, usually racemose, erect, horizontal, or pendulous; floral bracts usually insignificant. Flowers extremely variable in color and shape, often showy, very small to large, resupinate or not resupinate, usually spreading, ephemeral or long-lived. Sepals similar, free, short to filiform; lateral sepals adnate to elongated column foot and part of lip to form a mentum, 0.1-3 cm. Petals free, margin entire to fimbriate; lip entire to distinctly 3-lobed, base joined to column foot, sometimes narrowly clawed at base, sometimes forming a closed spur with lateral sepals to which it may be joined laterally for a short distance; disk with 1 to several keels, sometimes verrucose-papillose, calli rarely present, sometimes with a transverse basal ridge. Column short, stout; foot long, sometimes with a protuberance adaxially; apical stelidia obscure to distinct; viscidium present; pollinia 4 in appressed pairs, waxy, ovate or oblong, naked, i.e., without caudicles or stipes.

About 1,100 species: India across to Japan, south to Malaysia and Indonesia, east to Australia, New Guinea, and the Pacific islands; 78 species (14 endemic) in 14 sections in China.

See the monograph by Seidenfaden (Opera Bot. 83: 1-295. 1985) and the book by H. P. Wood (Dendrobiums. 2006).

After publication of the treatment for the Flora of China, one species was newly recorded from China (see JIN Xiao-Hua et al. 2010. Acta Bot. Yunnan. 32: 331-333, i.e., Dendrobium praecinctum Rchb. f.).

Key to sections

1 Stems with up to 4 internodes near base swollen and fleshy to form distinct fusiform pseudobulbs, upper part of stem thin and wiry; flowers ephemeral.   12 D. sect. Crumenata (p. 395)
+ Stems uniformly thick, fleshy or not, or fusiform, ovoid, or clavate; flowers ephemeral to long-lived   (2)
2 (1) Stems uniformly narrow, often wiry, internodes never fleshy or swollen   (3)
+ Stems with most internodes fleshy and swollen   (5)
3 (2) Leaves leathery or thinly leathery, dorsiventral, grasslike.   1 D. sect. Grastidium (p. 372)
+ Leaves thick and fleshy, cylindric, subcylindric, or laterally compressed and shortly ensiform   (4)
4 (3) Leaves laterally compressed and shortly ensiform, 5-6 mm wide; mentum 5-7 mm.   13 D. sect. Aporum (p. 396)
+ Leaves subulate-cylindric or subcylindric, 1.5-3 mm wide; flowers pale yellow, large; dorsal sepal ca. 12 mm; mentum ca. 20 mm.   14 D. sect. Strongyle (p. 397)
5 (2) Leaf sheaths, sometimes also leaf blade and inflorescence, with blackish or dark brown hairs.   10 D. sect. Formosa (p. 391)
+ Leaf sheaths, leaf blades, and inflorescences glabrous   (6)
6 (5) Leaf sheaths insignificant; stems fusiform to clavate, swollen, often angled, sometimes compressed, with 1-5 ± sheathless leaves clustered at apex; flowers mostly in pendulous, many-flowered racemes from upper nodes.   2 D. sect. Densiflora (p. 374)
+ Leaf sheaths distinct, often covering most of internodes; otherwise without above combination of characters   (7)
7 (6) Inflorescences several, lateral or subterminal on current year’s stem; flowers several, small; lip 3-lobed; stems often tufted, often small.   11 D. sect. Stachyobium (p. 393)
+ Inflorescences lateral, usually on leafless stems, pendulous or vertical on stem, most often with a short peduncle; flowers most often solitary or few, sometimes fascicled, rarely many on a longer raceme; plants often rather large and robust   (8)
8 (7) Mid-lobe of lip hairy   (9)
+ Mid-lobe of lip glabrous   (11)
9 (8) Mid-lobe of lip fringed.   7 D. sect. Stuposa (p. 389)
+ Mid-lobe of lip downy   (10)
10 (9) Inflorescences many per stem, few flowered; flowers mostly purple or white, less often yellow; lip usually with expanded mid-lobe.   3 D. sect. Dendrobium (p. 376)
+ Inflorescences few, distal, often only 1 per stem, many flowered; flowers usually yellow; lip expanded.   4 D. sect. Holochrysa (p. 384)
11 (8) Flowers usually with a short, saccate mentum   (12)
+ Flowers with a long narrow mentum; lip with a long narrow claw   (13)
12 (11) Inflorescences 1(or 2)-flowered, on leafy stems; dorsal sepal ca. 8 mm; mid-lobe of lip with distinct keels.   5 D. sect. Distichophylla (p. 388)
+ Inflorescences 2-6-flowered, on leafless stems; dorsal sepal 13-20 mm; mid-lobe of lip without keels.   6 D. sect. Breviflora (p. 388)
13 (11) Lip abruptly broadened from a narrow claw, not forming a spurlike structure with column foot; mentum pointing away from ovary.   8 D. sect. Calcarifera (p. 390)
+ Lip gradually broadened over its length, with a narrow base that forms a spurlike structure (closed spur) with column foot; mentum held parallel to ovary.   9 D. sect. Pedilonum (p. 390)

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