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Published In: Flora Cochinchinensis 2: 425 [as Phynchosia], 460. 1790. (Sept 1790) (Fl. Cochinch.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/29/2017)
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Rhynchosia Lour. (Grear, 1978)

Plants perennial herbs (shrubs elsewhere), with thick, woody rootstalks. Stems prostrate or trailing to ascending, climbing, or rarely erect, usually twining, ridged or angled, unarmed, densely pubescent with mostly downward-angled or -curved hairs (variously hairy elsewhere). Leaves pinnately trifoliate or the lowermost leaves sometimes lacking lateral leaflets and thus appearing simple, the petioles of the lowermost leaves long, progressively shorter toward the stem tip, the uppermost leaves short-petiolate, the petioles all densely hairy, the terminal leaflet stalk 5–20 mm long. Stipules narrowly lanceolate to ovate, sharply pointed at the tip, mostly shed early; stipels absent (present elsewhere). Leaflets broadly ovate to elliptic, somewhat rhombic, or nearly circular, the lateral leaflets sometimes somewhat asymmetric with an oblique base, otherwise rounded to broadly angled at the base, rounded or more commonly angled to a bluntly or sharply (but broadly) pointed tip, the margins entire, short-hairy, the upper surface moderately to densely pubescent with short, fine, spreading to curved hairs, the undersurface spreading-hairy, mostly along the veins, also dotted with minute, yellow to orange, more or less globose resin glands, the venation pinnate but with 3 main veins from the leaflet base, raised on the undersurface. Inflorescences axillary, short to elongate racemes or small clusters, the stalk mostly short, the bracts 3–7 mm long, linear to narrowly lanceolate, mostly shed early; bractlets absent. Calyces moderately to densely pubescent with fine, ascending hairs, sometimes mostly along the nerves and margins, also dotted with minute, yellow to orange, more or less globose resin glands, often becoming slightly enlarged at fruiting, the tube bell-shaped (cylindric elsewhere), shorter than the lobes, more or less 2-lipped, the upper 2 lobes fused to at or above the midpoint, the free portions narrowly triangular-ovate, the lower 3 lobes as long as or slightly shorter than the other lip, narrowly oblong-elliptic to lanceolate, all of the lobes angled or tapered to sharply pointed tips. Corollas papilionaceous, not much longer than the calyx, the petals lemon yellow to orangish yellow, the banner occasionally streaked with red or reddish-tinged on the outer surface, short-stalked, the expanded portion with a pair of small, incurved auricles at the base, obovate to nearly circular, rounded to minutely notched at the tip, shallowly keeled, strongly curved or bent backward from toward the base (but the flowers sometimes not fully opening), glabrous or short-hairy on the outer surface, the wings oblong-obovate with a minute auricle at the base, straight or nearly so, rounded at the tips, the keel oblong, somewhat curved upward, bluntly pointed at the tip. Stamens 10, all of similar lengths, 9 of the filaments fused and 1 free to about the midpoint, the fused portion longer than the free portion, curved upward toward the tip, the anthers small, attached below the midpoint, yellow, often darker-colored around the attachment. Ovary sessile, densely hairy and usually also glandular, the style curved upward, thickened toward the tip, glabrous, the stigma terminal, minute. Fruits legumes, oblong to elliptic-oblong or asymmetrically ovate in outline, flattened not or only slightly narrowed or indented between the seeds, tapered asymmetrically to a short beak at the tip, the 2 valves dark brown at maturity, densely hairy and dotted with minute, more or less globose glands, dehiscent, the valves becoming contorted or somewhat spirally twisted during dehiscence, (1)2-seeded. Seeds in our species 3–4 mm long, broadly oblong to more or less circular in outline, flattened, the surface brown, reddish brown, gray, or black, sometimes with darker mottling, smooth, shiny. About 230 species, nearly worldwide, most diverse in tropical regions.

Rhynchosia is recognized by the gland-dotted, trifoliate leaves, yellow corollas, and small, mostly 2-seeded legumes. Grear (1978) noted that in most of the species the flowers frequently do not open fully and that they do not produce significant quantities of nectar. During his extensive field work he never observed insects actually visiting Rhynchosia flowers. He concluded that the species are most commonly self-pollinated, which would limit opportunities for interspecific hybridization. Earlier bagging studies by Walraven (1967) indicated that all American species of Rhynchosia are self-fertile, with pollination occurring before the flowers open. There were no obvious meiotic irregularities noted in that study that might indicate that any hybridization had occurred.

In his revision of the genus, Grear (1978) cited a collection of R. minima (L.) DC. (least snoutbean) made by Reverchon in 1903 at Sheldon, which he mistakenly mapped from Vernon County, Missouri. Julien Reverchon (1834–1905) was an inveterate collector of the Texas flora, but although his personal herbarium was acquired by the Missouri Botanical Garden after his death there is no evidence that Reverchon ever botanized in the state of Missouri. The specimen cited by Grear (1978) actually originated from a Sheldon located near Houston, Texas, rather than the one in Missouri. Rhynchosia minima is an Old World species that is widespread as a presumed introduction in Latin America, the New World range extending northward sporadically into the southern United States, from Texas and southeastern Arkansas eastward to Georgia. Within the genus, it does not appear to be closely related to the two Missouri taxa, differing morphologically in a syndrome of floral features, especially its relatively short calyx lobes and smaller corollas, as well as its relatively long, curved fruits.


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1 Stems prostrate to loosely ascending or rarely erect, not twining or only loosely twining; inflorescences 1–6 cm long, condensed, umbellate clusters or short, dense racemes, mostly shorter than the subtending leaves; calyces 8–11 mm long Rhynchosia difformis
+ Stems trailing or climbing, twining; inflorescences 5–18 cm long, elongate, relatively open racemes, longer than the subtending leaves; calyces 10–14 mm long Rhynchosia latifolia
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