Hylodesmum
ascending to erect or spreading, terete, usually pubescent, rarely glabrous.
whorled or alternate, usually odd-pinnate, rarely unifoliolate;
stipules present, usually scarious, rarely thinly papery, striate, glabrate or hairy;
petiolate;
leaflets usually 3, rarely 1 [5 or 7], stipels present or absent, sometimes partly or wholly, filiform, usually reduced, scarious, blade margins entire, rarely undulate, ciliate, surfaces pubescent.
2–26-flowered, terminal, sometimes also axillary, sometimes a fertile shoot separately arising from basal part of vegetative stem, pseudoracemes, sometimes in panicles, lax-flowered, branched or unbranched;
bracts caducous, primary ones subtending flower cluster with secondary bracts each subtending 1 pedicel.
densely uncinate-puberulent or glabrous.
papilionaceous;
calyx broadly campanulate, lobes 5, usually appearing 4-lobed, adaxial pair connate except apically, with 2 minute teeth, lobes shorter than tube;
corolla pink, pink-purple, or white [orange, red], banner clawed or tapering proximally, blade usually broadly obovate, often with pair of spots (false nectar guides) at base;
wing and keel petals clawed, keel usually connate along abaxial margin of blade (distinct in H. pauciflorum);
stamens 10, monadelphous;
anthers dorsifixed;
ovary stipitate.
loments, distinctly stipitate, stipe exserted from calyx, greater than 5 mm, glabrous or puberulent, compressed, very deeply incised abaxially, straight or shallowly undulate adaxially, 1–4-jointed, lateral faces densely uncinate-puberulent;
segments obliquely depressed or very shallowly obovate or obtriangular;
sutures glabrate, abaxial suture very deeply incised, adaxial distinctly thickened, connections between segments (isthmi) less than 1/5 as broad as pod.
2–5, flat, obliquely depressed-obovate, broadest 2/3 distance towards anterior end, without rim-aril around hilum;
cotyledons of seedlings hypogeous, remaining underground being enclosed in loment-segment, rarely epigeous.
= 11.
Hylodesmum
Species ca. 11 (3 in the flora).
Plants of Hylodesmum and Desmodium are alike in having three-foliolate leaves and uncinate-puberulent loments that are easily separable into 1-seeded segments; Hylodesmum differs from Desmodium in having calyx lobes shorter than the tubes, monadelphous stamens, long-stipitate loments with abaxial sutures incised to the adaxial sutures, shallowly obtriangular segments, and seeds without a rim-aril around the hilum.
Phylogenetic relationships between the three North American species were illustrated in the phylogenetic trees in K. Ohashi et al. (2018b) and discussed by Li H. C. et al. (2019).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Inflorescences usually terminal, sometimes axillary; corollas white; keel petals distinct (reproductive organs exposed); loment stipe uncinate-puberulent; stipels sometimes present. | H. pauciflorum |
1. Inflorescences terminal or on peduncles from bases of plants; corollas usually pink or pink-purple, rarely white; keel petals connate along abaxial margin (enclosing reproductive organs); loment stipe glabrous or glabrate; stipels usually absent, rarely present. | → 2 |
2. Inflorescences terminal; pedicels 3–8 mm, stout; terminal leaflet blades broadly ovate, apex abruptly acuminate; stipules often persistent; loment stipe 4–10 mm. | H. glutinosum |
2. Inflorescences on peduncles arising from bases of plants; pedicels 10–25 mm, slender; terminal leaflet blades rhombic, elliptic, obovate, or orbiculate, apex acute or short- acuminate; stipules deciduous; loment stipe (5–)10–22 mm. | H. nudiflorum |
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