Rhynchosia caaguazuensis Hassl.,Bull.Herb.Boissier, 1907

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 : 17-18

4. Rhynchosia caaguazuensis Hassl.,Bull.Herb.Boissier 7: 168.1907. Type :— PARAGUAY, “in campis pr. Caaguazú ”, February 1905 (fl.), E. Hassler 9013 (Lectotype, first-step designated by Grear [1978]; second-step designated here: G 00400136 [digital image!]; isolectotypes: BM 000538508 [digital image!], F 0059811 [digital image!], G 00400137 [digital image!], GH 00063819 [digital image!], K 000484041 [digital image!], MPU 022980 [digital image!], NY 00026941[!], P 00708589 [digital image!], S S-R-9722 [digital image!], UC 929041 [digital image!]). ( Fig. 4 C )

Subshrub erect, stems branched, sericeous, indumentum white, with yellow vesicular glands, but lacking bulbous-based trichomes. Stipules 0.5–1 × 0.5 mm, free, caducous, triangular, externally villous with yellow vesicular glands, but lacking bulbous-based trichomes. Leaves trifoliolate; petiole 0.3–0.7 cm long; leaf rachis 0.2–0.4 cm long; stipels lacking; leaflets 1.3–4.3 × 0.4–1.2 cm, linear, narrowly elliptical, or oblong, surface not bullate, obtuse to rounded at apex, cuneate to obtuse at base, margin revolute, sericeous to tomentose, with yellow vesicular glands on both surfaces. Inflorescences axillary or terminal, racemose, 1.2–4.2 cm long, bearing 3–12 flowers, not exceeding the length of the subtending leaf; bracts caducous; pedicel 2–3 mm long. Flowers 7–12 mm long excluding the pedicel; calyx 5.5–9 mm long, pubescent with yellow vesicular glands, but lacking bulbous-based trichomes, lobes lanceolate, not exceeding the corolla in length; standard petal 7.5–9 × 4–5 mm, oblong to elliptical or emarginate at apex, densely pilose, with vesicular glands but lacking bulbous-based trichomes, claw 2–2.5 mm long, auricle ca. 0.5 mm long; wing petals 7–8 × 1–1.5 mm, oblong, claw 1.5–2 mm long, auricle ca. 0.5 mm long; keel petals 8–9 × 2–2.5 mm, falcate, claw 2–2.5 mm long; stamens 7.5–8.5 mm long; ovary 2–2.5 mm long, pubescent, with yellow vesicular glands. Fruits 1.4–2.2 × 0.5–0.7 cm, greenish to brownish, without constrictions between the seeds, elliptical to ovate-elliptical, pilose to pubescent, with yellow vesicular glands but lacking bulbous-based trichomes. Seeds 3.5–4 × 3–4 cm, reniform to suborbicular, unicolored, reddish-brown to brown.

Nomenclatural and taxonomic notes: — Hassler (1907) described R. caaguazuensis based on the collection Hassler 9013, but he did not specify a particular specimen as type. There are several duplicates of this collection deposited in different herbaria. Grear (1978) cited a specimen at G as the holotype, but this citation constitutes an inadvertent lectotypification (see Turland et al. 2018, Art. 9.10, Ex. 11; Prado et al. 2020). As there are three duplicates of this collection housed in G (G 00379289, G 00400136 and G 00400137) and Grear (1978) did not specify which of them is the type, his type designation constitutes the first-step in the lectotypification of the name (see Turland et al. 2018, Art. 9.17). Our designation of the specimen with barcode number G 00400136 constitutes the required second-step.

Rhynchosia caaguazuensis is easily distinguished from other species of the genus in South America. It is characterized by its erect subshrub habit, its leaves short-petiolate (the petiole 0.3–0.7 cm long) and by its linear, narrowly elliptical, or oblong leaflets, up to 1.2 cm wide and with revolute margins ( Fig. 4 C ).

Reproductive phenology: —Flowering and fruiting in February and November.

Distribution and habitat: — Rhynchosia caaguazuensis is endemic to Paraguay ( Fig. 3 ). It grows in areas of the Cerrado domain, such as campos rupestres (rocky fields). The species is very rare with few specimens in herbaria.

Conservation status: —Critically Endangered (CR, based on criterion D). Rhynchosia caaguazuensis was first described in 1907 and has been collected only three times since then.

Selected Specimens Examined:— PARAGUAY. Caaguazú: “Dans les campos”, 16 November 1874 (fl./fr.), B. Balansa 1499 (P 02749393). Canendiyú, Mbaracayú Natural Reserve , 14 January 1998 (fl.), E. M. Zardini & M. Vera 47878 ( MEXU 1161266 ); “In regione calcarea cursus superioris fluminis Apa”, s.d. (fl./fr.), E. Hassler 11067 ( NY, P 2749397 ) .

Figures

FIGURE 3. Geographical distribution of Rhynchosia arenicola, R. balansae, R. burkartii and R. caagazuensis in South America.

FIGURE 4. Detailed structures of Rhynchosia species. A–B. Portion of the stem and detail of fruit of R. burkartii. C. Stem of R. caaguazuensis showing the leaflets shape and inflorescences. D–E. Fruit of R. erythrinoides. F, G. Portion of the stem and detail of fruit of R. mantaroensis var. cuprinervia. (Illustrated by Klei Souza).