Stylosanthes
pencil-flower
prostrate to erect or ascending, sometimes viscid, pubescent or glabrous.
alternate, odd-pinnate;
stipules present, foliaceous, amplexicaul, adnate to petiole for most of its length;
petiolate;
leaflets 3, blade margins entire, surfaces glandular-punctate or epunctate, sometimes black-punctate, glabrous or pubescent.
1–15+-flowered, terminal or axillary, spikes or solitary flowers, erect, axis rudiment (aborted floral axis) sometimes present;
bracts present, persistent, foliaceous;
bracteoles persistent, 1 outer, 1 or 2 inner.
papilionaceous;
calyx tubular, lobes 5, unequal, adaxial 4-lobed;
corolla yellow or orange-yellow, inserted near apex of calyx tube;
petals evenly graduated;
wings shorter and narrower than banner, not adnate to keel, clawed, auriculate;
keel incurved or rostrate;
stamens 10, monadelphous;
anthers dimorphic, 5 versatile anthers alternating with 5 sub-basifixed;
ovary subsessile;
style curved, glabrous or pubescent.
loments, sessile or stipitate, tan or brown, compressed, articulate, ovate, individual segments indehiscent, glabrous or pubescent;
segments 2, breaking apart, proximal segment fertile or abortive, densely pubescent, distal segment fertile, reticulate;
style persistent as a beak, beak erect, declined, or coiled.
1 or 2, black, compressed, ovoid, shiny.
= 10.
Stylosanthes
Species 37 (5 in the flora).
The alternation of sub-basifixed and versatile anthers and the absence of stipels in Stylosanthes suggest a relationship to Arachis, Chapmannia, and Zornia. Molecular phylogenetic analyses support a close relationship among Arachis, Chapmannia, and Stylosanthes but place Zornia more distantly (M. Lavin et al. 2001). Stylosanthes resembles Zornia morphologically because of the large bracts subtending each flower and the often spicate inflorescences. The leaves of Stylosanthes are three-foliolate, the ovules are two or three, and bracteoles are present; the leaves of Zornia are two- or four-foliolate, the ovules are two to several, and bracteoles are absent. Species of Stylosanthes in sect. Stylosanthes have an axis rudiment (an aborted floral axis) next to the flower; species in sect. Astyposanthes (Herter) Mohlenbrock lack an axis rudiment.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Inflorescences: axis rudiment present; inner bracteoles 2. | → 2 |
2. Loments: beak straight or slightly curved; leaflet blade surfaces glabrous (rarely with marginal cilia); teeth of distal stipules mostly longer than sheath; calyx tubes 3–4 mm. | S. calcicola |
2. Loments: beak hooked; leaflet blade surfaces glabrous or short-pilose; teeth of distal stipules mostly shorter than sheath; calyx tubes 4–7.5 mm. | S. hamata |
1. Inflorescences: axis rudiment absent; inner bracteole 1. | → 3 |
3. Loments: beak to 1/5 as long as distal segment. | S. biflora |
3. Loments: beak to 1/2 as long as or exceeding distal segment. | → 4 |
4. Stems with viscid hairs; leaflet blade surfaces punctate abaxially; banners 4–7 mm; loment beak to 1/2 as long as distal segment. | S. viscosa |
4. Stems glabrous or short-hispid, not viscid; leaflet blade surfaces without punctations; banners 3–4 mm; loment beak equaling or surpassing distal segment. | S. humilis |
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