Rhynchosia difformis (Elliott) DC.
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Authority
Grear, John W. 1978. A revision of the New World species of Rhynchosia (Leguminosae-Faboideae). Mem. New York Bot. Gard. 31 (1): 1-168.
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Family
Fabaceae
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Scientific Name
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Description
Species Description - Prostrate or twining (rarely erect), herbaceous vine, to 4 m, from woody rootstock, the stems one to several, simple or branching, strongly angled, finely to loosely strigose or hirsute, the hairs tawny to silvery. Stipules ovate or ovate-lanceolate, acute or long-acuminate, persistent, 3-8(-10) mm long, 1.5-3 mm wide. Petioles angled, hirsute, (l-)2-5(-6.5) cm. Leaflets 3 (the lowermost often one and reniform or deltoid), thin-coriaceous, ovate to ovate-rhombic and orbicular or obovate to obovate-elliptic and elliptic, apex acute, obtuse, rounded or rarely retuse, base obtuse to rounded or subcordate, 2-5(-6) cm long, l-6.5(-8) cm wide, strigulose to glabrate above, hirsutulous or strigulose to loosely strigose beneath, gland-dotted on both surfaces, but more so beneath, terminal petiolule 0.5-2 cm, the laterals 1-5 mm, stipels lacking. Inflorescences short, of 2-20 flowers, non-branching, not exceeding the leaves, (l-)2-5(-6.5) cm, peduncle subobsolete to 2(-4) cm, pedicels 2-5 mm. Bracts linear to narrowly lanceolate, long-acuminate, caducous, 3-7 mm long, 0.5-1.5 mm wide. Calyx equalling or exceeding the corolla, hirsute or hirsutulous, 9-12 mm, tube 1-2 mm, lobes widely lanceolate or ovate-lanceolate, 6-10 mm, vexillar sinus 3-5 mm. Corolla deep yellow or orange-yellow, 8-10 mm. Standard broadly obovate, with pair of small internal callosities, emarginate, glabrous to puberulous, 8-10.5 mm long, 5-6 mm wide, auricles 0.5-1 mm, claw 1-2 mm. Wings oblong, glabrous, 7-8 mm long, 1.5-2 mm wide, claw 2-2.5 mm. Keel blades falcate, glabrous, 7-8 mm long, 2-3 mm wide, claw 2-3 mm. Stamens 7-9 mm. Fruits ovate-oblong, compressed, puberulous and hirsute intermixed, gland-dotted, 14-20 mm long, 6-9 mm wide, beak 0.5-1 mm. Seeds suborbicular, compressed, brown, black or mottled, 34 mm long, 34 mm wide, hilum ovate, 1 mm, strophiole lobes cuneate.
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Discussion
Glycine tomentosa Linnaeus, Sp. PI. 2: 754. 1753, pro parte quoad paratypum. Glycine tomentosa var ß volubilis Michaux, Fl. Bor.-Am. 2: 63. 1803. Arcyphyllum difforme Elliott, Jour. Acad. Phila. 1: 372. 1817. Glycine tomentosa sensu Pursh, Fl. Am. Sept. 2: 486. 1814;Nuttall, Gen. N. Am. Pl. 2: 114. 1818; Elliott, Sketch 2: 234. 1822; non G. tomentosa Linnaeus, 1753 sensu str. Rhynchosia tomentosa var y volubilis (Michaux) Torrey & Gray, Fl. N. Am. 1: 284. 1838. Dolicholus tomentosus (Linnaeus) Vail, Bull. Torrey Club 26: 112. 1899. Rhynchosia volubilis sensu Wood, Class-Book 321. 1896, non R. volubilis Loureiro, 1793. Rhynchosia reticulata sensu Chapman, Fl. So. U. S. 115. 1897, non R. reticulata (Swartz) de Candolle, 1825. Dolicholus lewtonii (“lewtoni”) Vail, Bull. Torrey Club 26: 113. Type: FLORIDA. Orange County, F. L. Lewton sn, 7 Jul 1894 (holotype, NY!; isotype, NY!). Rhynchosia lewtonii (Vail) Schumann, Bot. Jahrb. 27(1): 496. 1901, in synon. Rhynchosia lewtonii (Vail) Small, Man. S. E. FI. 714. 1933. Dolicholus tomentosus var undulatus Vail, Bull. Torrey Club 26: 113. 1899. Type: FLORIDA. Dr. Chapman s n, 1846. (holotype, MO-1827636!; paratypes, A. H. Curtiss 660, F!, GA!, GH!, LE!, MISSA!, MO!, NY!, PH!, S!). Type. VIRGINIA, “ex herb. Gronovii.” Clayton 730, w/o date (holotype, BM!). Linnaeus confused two very different species, R. tomentosa and R. difformis, under one name. Local Names. Twining rhynchosia (eastern U. S.). The original description of R. difformis Linnaeus was based on a mixture of true R. difformis and R. tomentosa, collected in Virginia by Clayton and first described in polynomial terms by Dillenius and Gronovius. Neither of these authors, nor Linnaeus, was aware that they were treating two distinct species as one. The mistake was perpetuated by later botanists and what is now properly called R. difformis continued to be known as R. tomentosa until Fernald cleared up the confusion in 1942. The complexities stemming from these discordant elements were discussed fully by Fernald and require no comment here. However, when consulting early literature pertaining to R. difformis it should be remembered that the species is called R. tomentosa by all authors prior to 1942 while the typical variety of R. tomentosa passes as R. erecta in earlier works. In 1899, Vail described R. lewtonii, based on only a few plants collected in central Florida. I have seen only six specimens of what could be called R. lewtonii and they appear to be extreme forms of R. difformis with larger, thinner leaflets which tend to be rounded rather than acute at the apex. However, R. difformis, as the name implies, is quite variable as to leaflet shape and size. The corolla is consistently glabrous with the exception of the standard which can vary from glabrous to puberulous. The type specimens of R. lewtonii appear to be portions of the upper stems, which have been broken off well above ground level and bear only trifoliolate leaves. Basal stem portions might have contained some unifoliolate leaves as is usually the case with stems of R. difformis. In the protologue of R. lewtonii, Vail states that it is allied to R. michauxii, but actually points out more differences than similarities between the two, as follows; “Allied to D. Michauxii Vail, from which it differs in the trifoliolate, abnormally large leaves, which are notably broadest above the middle and with narrow and less prominent subcordate bases. The calyx and corolla are also smaller than those of D. Michauxii and the racemes are longer.” It actually has more in common with R. difformis than with R. michauxii, which is placed in series 5 in this treatment based on calyx characters. Walraven (1970b) also considers Vail’s species as a distinct entity but suggests it should be considered a variety of R. michauxii. However, there is no definite statement that a formal taxonomic change in rank is being made and R. difformis var michauxii is not listed in the synonymy of R. difformis. Walraven himself states that his statistical analysis is highly subjective but it becomes even less so if one has access to as much material as possible from as wide a range as possible and judgment is based on more constant, reliable characters. A careful comparison of extensive collections of both R. difformis and R. michauxii indicates that R. lewtonii, although an extreme form, falls within the range of variation exhibited by R. difformis and it is being considered synonymous with that species. In 1899, Vail also segregated a variety of R. difformis (Dolicholus tomentosus var undulatus) based almost entirely on a few populations with undulate leaflet margins. I have examined most of the type material of this so-called variety and, with the exception of the wavy leaflet margins (which appear to be a reflection of uneven pressure applied during pressing and drying), the plants are the same as typical R. difformis. Any attempt to segregate a varietal entity on the above character could only be achieved artificially. Rhynchosia difformis has its western limit of distribution in eastern Texas, where it is represented by only a few collections. These plants have mostly erect stems, as exemplified by the collections of Turner & Tharp (3083) and by Lay (sn, 27 Aug 1947). The change in habit could be due to introgression with R. tomentosa where their ranges overlap. Although the stems are erect, the calyx is more like that of R. difformis. Turner (1959) is also of the opinion that the two species intergrade in Texas and points out the occurrence of erect forms of R. difformis which also look very much like R. tomentosa.
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Distribution
Distribution. Southeastern coastal plain (Southeastern Virginia to eastern Texas) (Fig. 32). Occurring in dry sandy soils of pinelands and in fallow fields and clearings; at low elevations.
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