Rhynchosia Lour., Fl. Cochinch.

Bezerra, Luísa Maria De Paula Alves, Cândido, Elisa Silva, Vargas, Wanderleia De, Torke, Benjamin Marland, Lewis, Gwilym Peter & Perez, Ana Paula Fortuna, 2024, Taxonomic revision of Rhynchosia Lour. (Leguminosae, Papilionoideae, Phaseoleae) in South America, Phytotaxa 643 (1), pp. 1-67 : 7-10

Rhynchosia Lour., Fl. Cochinch. 425, 460. 1790, nom. cons.

Type species:— Rhynchosia volubilis Lour., Fl. Cochinch. 2: 460. 1790. CHINA, “Habitat inculta prope Cantonem Sinarum”, s.d (fl.), Loureiro 562-1 (Holotype: P 00150846 [digital image!]) .

Dolicholus Medik, Vorles. Churpfälz. Phys. -Ökon. Ges. 2: 354. 1787. nom. rej.

Type species: Dolicholus flavus Medik. , nom. illegit. [= Rhynchosia minima (L.) DC.].

Cylista Aiton, Hort. Kew. 3: 36, 512. 1789. nom. rej.

Type species: Cylista villosa Ait. [= Rhynchosia hirta (Andrews) Meikle & Verdcourt ].

Arcyphyllum Elliott, J. Acad. Nat. Sci. Philadelphia. 1(2): 371–372. 1818.

Type species: Arcyphyllum simplicifolium (Walter) Elliot [= Rhynchosia reniformis DC ].

Polytropia C. Presl, Symb. Bot. 1: 21. 1831.

Type species: Polytropia ferulaefolia C. Presl [= Rhynchosia ferulifolia (C. Presl) Benth. ex Harv. ].

Cyanospermum Wight & Arn., Prodr. Fl. Ind. Orient. 1: 259. 1834.

Type species: Cyanospermum tomentosum Wight & Arn. [= Rhynchosia hirta (Andrews) Meikle & Verdcourt ].

Nomismia Wight & Arn., Prodr. Fl. Ind. Orient. 1: 236. 1834.

Type species: Nomismia nummularia Wight & Arn. [= Rhynchosia nummularia DC. ].

Pitcheria Nutt., J. Acad. Nat. Sci. Philadelphia 7: 92. 1834.

Type species: Pitcheria galactoides Nutt. [= Rhynchosia cytisoides (Bertol.) Wilbur ].

Chrysoscias E. Mey., Pl. Afr. Austr. 139. 1836.

Type species: Chrysoscias grandiflora E. Mey [= Rhynchosia chrysoscias Benth. ex Harv. ].

Copisma E. Mey., Comm. Pl. Afr. Austr. 132. 1836.

Type species: Copisma tottum E. Mey. [= Rhynchosia totta (Thunb.) DC. ].

Hidrosia E. Mey., Pl. Afr. Austr. 89 (1836)

Type species: Hidrosia bullata E. Mey [= Rhynchosia bullata (E. Mey.) Benth. ex. Harv.].

Orthodanum E. Mey., Comment. Pl. Africae Austr. 131. 1836.

Type species: Orthodanum latifolium E. Mey [= Rhynchosia sordida (E. Mey.) Schinz ].

Sigmodostyles Meisn., J. Bot. 2: 93. 1843.

Type species: Sigmodostyles villosa Meisn. [= Rhynchosia villosa (Meisn.) Druce ].

Stipellaria Klotz., Schomb. Faun. Fl. Brit. Gui. 3: 1203. 1848, nom. nud.

Baukea Vatke, Linnaea 43: 104. 1881.

Type species: Baukea insignis Vatke [= Rhynchosia baukea Du Puy & Labat ].

Leycephyllum Piper, J. Washington Acad. Sci. 14: 363. 1924.

Type species: Leycephyllum micranthum Piper [= Rhynchosia erythrinoides Schltdl. & Cham. ].

Leucopterum Small, Man. S.E. Fl. : 713. 1933.

Type species: Leucopterum parvifolium (DC.) Small [= Rhynchosia parvifolia DC. ].

Erect herbs or subshrubs or prostrate or twining vines, sometimes with a pronounced woody underground system. Stems simple or branched. Stipules free, persistent or deciduous. Leaves unifoliolate or trifoliolate, sessile or petiolate; stipels present or absent. Leaflets variously shaped, with yellow vesicular glands on both surfaces or just abaxially. Inflorescences racemose, corymbiform, fasciculate or paniculate, terminal or axillary, few- to many-flowered. Bracts linear to lanceolate, caducous. Corolla papilionaceous, yellow, sometimes with red nectar guides, glabrous or with an indumentum; calyx campanulate, 5-lobed, indumented, with vesicular glands or bulbous-based trichomes; calyx lobes shorter, equaling, or exceeding the length of the corolla, linear, lanceolate to ovate; standard oblong to obovate or orbicular, 2-auriculate and clawed at base; wing petals oblong to obovate, uni-auriculate and clawed at base; keel petals fused, falcate, clawed at base. Stamens 10, diadelphous, the vexillary one free, anthers uniform and dorsifixed. Ovary sessile to subsessile, pilose to pubescent, biovulate, sometimes uniovulate by abortion; style filiform, stigma apical, subcapitate. Fruit 2-valved, dehiscent, oblong, falcate, elliptical, ovate to obovate, indumented or glabrescent, sericeous, pilose, pubescent to hirsute, constricted between the seeds or not, plump or laterally compressed, with vesicular glands or bulbous-based trichomes. Seeds usually two per pod, sometimes one by abortion, suborbicular, reniform, ovate to oblong, brown to black or bicolored black and red, yellow or orange; hilum long, linear to ovate, insertion on the funicle central, sub-central or terminal.

Etymology: —The name Rhynchosia is derived from the Greek word “ rhynchos ’’ which means “beak” in reference to the shape of the keel petals of the type species, Rhynchosia volubilis Loureiro (1790: 460) ( Grear 1978).

Geographical distribution, habitat and species number: —Ca. 230 species are distributed in tropical and subtropical areas around the globe, with 27 species in South America. The South American species are distributed in a variety of open and forested habitats, with the greatest diversity concentrated in the Cerrado domain ( Fig. 1 ). Most of the South American taxa are widely distributed in this region and some also occur in Central and North America. However, R. caaguazuensis Hassler (1907: 168) is endemic to Paraguay, and R. franciscana , R. lewisii , R. mineira and R. platyphylla Bentham (1862: 201) are endemic to Brazil. Rhynchosia minima is the only species that has a cosmopolitan distribution.

In Grear’s (1978) revision of the Neotropical species of Rhynchosia , 26 species were recognized for South America. Since then, five new species were described from South America: R. naineckensis , R. edensis Izaguirre & Beyhaut (1997: 134) , R. franciscana , R. lewisii , and R. mineira . Also, the species R. hagenbeckii Harms (1903: 29) was synonymized to R. balansae Micheli (1883: 31) , and one taxon, R. diversifolia var. prostrata Burkart (1967: 628) , was elevated to specific rank with a new name, R. bicentrica Turner (2012: 22) .

Grear (1978) recorded the species R. precatoria Candolle (1825: 385) and R. quercetorum Standley (1937: 555) in South America based on single records from Colombia for both species. We were unable to confirm the identities of these two specimens from analysis of digital images. Considering that no other South American material of either species was located, R. precatoria and R. quercetorum are not treated in this work. However, we note that there is substantial confusion surrounding the taxonomy of the Neotropical species with bicolored seeds, including these two species.

Ecology and economic importance: —Many species of Rhynchosia , as well as Eriosema , possess specialized root systems that confer resilience against cutting and burning ( Grear 1978; Cândido et al. 2019). These genera and other members of subtribe Cajaninae have characteristic secretory structures throughout the plant, such as bulbous-based trichomes and vesicular glands ( Vargas et al. 2018). Histochemical and ultrastructure analysis shows that the exudates of these structures act as defense against herbivory, and may also lessen damage by ultraviolet radiation ( Vargas et al. 2019).

Some species of Rhynchosia have attractive seeds. Regarding these South American species, the seeds are bicolored, red and black (yellow-orange and black in one species), with areas of coloration almost equal or the red just around the hilum. These hard and brightly-colored seeds, that in coloration resemble seeds with additional fleshy structures, but that do not offer food rewards to mutualistic frugivores, are called mimetic seeds ( Ridley 1930; Peres & Van Roosmalen 1996; Galetti 2002; Pizo et al. 2020).

A study that evaluates the temporal pattern of seed “rain” of the mimetic seeds of R. melanocarpa in an area of disturbed Cerrado vegetation in Rio Claro, São Paulo, Brazil, was performed by Pizo et al. (2020). This study revealed that the dispersal of such seeds benefits from the temporal heterogeneity found in Cerrado environments, where the availability of fleshy fruits varies greatly with time. The fruits of R. melanocarpa dehisce and the seeds become available early in the Cerrado fruiting season to profit from the less discriminating eating habits of birds in the dry season, as well as the influx of migratory bird species that are presumably naive with respect to the recognition of mimetic seeds.

It is commonly observed that in most species of Rhynchosia after dehiscence, the two valves usually tend to coil, especially in dry air, expelling their seeds ( Grear 1978, L.M.P.A. Bezerra, pers. obs.). However, in the case of those species that present mimetic seeds, that seeds remain attached to dehisced pods for long periods of time, increasing their availability to dispersing birds ( Brancalion et al. 2010). Also, the seeds of some Rhynchosia species with conspicuous strophioles may be dispersed over short distances by ants ( Grear 1978).

Species of Rhynchosia may be linked to increased virility, as in the case of R. pyramidalis ( Lamarck 1786: 296) Urban (1918: 318) , popularly known as “Pega Palo”, which gained some international notoriety by being known as “The Vine That Makes You Virile” ( Grear 1978). As mentioned by Grear (1978), stems sections were cut and placed in rum bottles until the liquor turns a dark brown. This drink it is said to have an effect somewhat like increasing virility and potency in young and old.

Some species of the genus, such as R. phaseoloides , also have narcotic properties and its seeds were used as hallucinogens by ancient Mexican cultures. These seeds have been found to contain alkaloids, but their toxic properties have not been characterized ( Schultes 1976). Although little is known about it, Grear (1978) mentioned that one species of Rhynchosia could also be used as food source for both humans and cattle. In addition, the showy seeds of some species are used in handicrafts and jewellery and some species that present attractive flowers, fruits and foliage are used for ornamentation ( Grear 1978; Jaca 2017).

Figures

FIGURE 1. Habitat of Rhynchosia species in Brazil. A, E. Grasslands and bushy woodland in Cachoeira do Campo, Minas Gerais state, Brazil. B. Sandy soil field in Rio Grande do Sul state, Brazil. C, D. Grasslands and bushy woodland in Botucatu, São Paulo state, Brazil. (A, B, C by L.M.P.A. Bezerra) and (D, E by T.C. Monteiro).