Macroptilium rubidum (Piper) C.L. Ribeiro, 2025

Ribeiro, Carolina Lima, Santos, Felipe Da Silva, Snak, Cristiane & Queiroz, Luciano Paganucci De, 2025, Morphological data and ecological niche modelling support the inclusion of Phaseolus rubidus in Macroptilium: Implications for Papilionoid Lineages in the Cerrado and Paraná Forests, Phytotaxa 697 (1), pp. 83-96 : 89-92

Macroptilium rubidum (Piper) C.L. Ribeiro , comb. nov. ≡ Basionym: Phaseolus rubidus Piper, Contr. U.S. Natl. Herb.

22(9): 680. 1926 ≡ Phaseolus rufus Micheli, Mém. Soc. Phys. Genève 28(7): 29. 1883 nom. illeg., non Phaseolus rufus Jacq., Hort. Bot. Vindob. 1:13. 1770 (= Phaseolus lunatus L.) ≡ Phaseolus monophyllus var. rufus (Micheli)

Hassl., Candollea 1: 448–450. 1923. Holotype: — Paraguay, Caaguazú in Campis, Nov., B. Balansa 1841 (P barcode

00226967!)

= Phaseolus monophyllus f. brevipetiolata Chodat & Hassl. in Bull. Herb. Boissier, sér. 2, 4(9): 909. 1904 ≡ Phaseolus monophyllus f. paraguariensis Hassl. in Candollea 1: 448–450. 1923 nom. superfl. Lectotype (designated here):— Paraguay, in Campo Nandurucay, Sierra de Maracayú, Act 1898–1899, E. Hassler 4932 (G barcode 00605339!; isolectotype: BM barcode 000538459!).

= Phaseolus monophyllus var. paraguariensis Chodat & Hassl. in Bull. Herb. Boissier, sér. 2, 4(9): 909. 1904. — Lectotype (designated here): Paraguay, in campis siccis galareosis pr. Bellavista, Apa, Dec., E. Hassler 8116 (G barcode 00605335!; isolectotypes: BM barcode 000538457!, G barcode 00605336!, 00605337!, GH barcode 00064120!, LY barcode 0205778!, P barcode 00708525!, W barcode 19040000042!).

= Phaseolus monophyllus var. intermedius Hassl. in Candollea 1: 448–450. 1923. — Lectotype (designated here): Paraguay, In campis siccis Punta Para flor. et fruct. mens, Dec., E. Hassler 9818 (BM barcode 000538460!; isolectotypes: LY barcode 0205779!, MPU barcode 1208504!). Remaining syntype: in regione fluminis Alto Paraná, Fiebrig 6254 (SI barcode 130544!).

Description:— Erect herb, main stem ca. 4 mm diam., internodes ca. 1 cm long, branches prostate with internodes 2.3–4.4 cm long, velutinous with red, yellow to translucent trichomes. Stipules 6–9 × 3–5 mm, ovate to triangular, acute, pubescent to velutinous, with 5–7 parallel veins, persistent. Leaves uni–bi–trifoliolate, usually basal leafs are unifoliolate and leaf of the prostrate branches are trifoliolate; petiole 15–44 mm long, canaliculate, velutinous, rachis 8–14 mm long, velutinous; stipels 2–3 mm long, linear, pubescent, persistent; petiolules 1–2 mm long, velutinous; leaflets ovate, elliptic or triangular, not lobated, base rounded or obtuse, apex rounded or obtuse and mucronate, membranaceous, velutinous to sericeous, soft in touch, more dense on abaxial surface, trichomes red to yellow, denser at the margins and veins, translucid trichomes in the center of the blade, venation actinodromous, 3–5-veined from the base, 5–6 pairs of lateral veins; lateral leaflets 31–49 × 17–28 mm, asymmetrical, the outer side (from the middle vein) 1.2–2.1× wider than the inner one; terminal leaflet 40–76 × 28–61 mm, symmetrical. Inflorescence an axillary pseudoraceme, erect, peduncle 16–35 cm long, reddish velutinous, peduncular bracts, at the base of peduncle, in two lateral tuffs of 2–6 bracts each; inflorescence rachis 6.5–20.2 cm long, reddish sericeous, floral nodosities 8–10, globose, 2.5–3.5 cm long between basal nodosities, 2 flowers per nodosity; peduncular bracts 4–7 mm long, linear, translucid sericeous, persistent; floral bracts oblong or linear, 3–5-parallel veined, sericeous, caducous; first order floral bracts (at the base of the nodosity) 3.2–3.4 mm long; second order floral bracts (at the base of the pedicel) 3.6–4.8 mm long; bracteoles (one pair at the apex of the pedicel) 2–2.3 mm long; pedicel ca. 0.9 mm long, sericeous. Flowers 9.2–18 × 6.3–8.8 mm, pre-anthesis floral bud 6.3–10.7 × 5.1–7.9 mm; calyx tube 2 × 2.4–3.1 mm, campanulate, rusty sericeous when dry, the 5 teeth much shorter than the tube, the two vexillary teeth 1.2 × 1.2–1.3 mm, deltoid, acute, lateral teeth 1.6–1.8 × 0.9 mm, carinal tooth 1.3–1.6 × 0.6–0.7 mm, triangular, acute; petals salmon-pink to orange, violet when dried, standard petal 6.5–7.9 × 7.3 mm with a claw 2.2–2.6 mm long, widely ovate, asymmetrical, two narrow auricles extending from the base of the claw to the center of the lamina, apex retuse, the lamina reflexing backwards about 90°, slightly twisted to the right, papillae on the auricle and between then; wing petals 5.9–8.9 × 8.3–9.4 mm with a claw 4.4–4.7 mm long, orbicular, claws strongly connate with base with the lamina of the keel petals and the estaminal tube, a rounded spur present near the base at the adaxial and inner margin; keel petals 9.4–10 × 1.6–1.9 mm with a claw 4.4–4.7 mm long, joined along both margins, straight claw strongly connate with staminal tube, proximal portion of the lamina straight and distal portion recurved in an almost complete turn, lacking a spur, rostrum ca. 6.1 mm long; androecium 11.2–13.1 mm long, hooked at the apex like the keel, diadelphous, with nine stamens joined into a staminal sheath at the basal portion and free at the distal portion, vexillary stamen free and thickened just above the base, anthers 0.4–0.5 mm long, uniform, dorsifixed with parallel thecae presenting different heights; intrastaminal disc shortly cylindrical with an irregularly lobed rim around the ovary base; ovary 3.4–3.7 × 0.6 mm, sessile, sericeous, 8–9-ovulate, style 8.2–9.6 mm long, filiform, straight base and apex recurved like the keel petals, stigma terminal, capitate, presenting a brush of hairs just below the stigma along the abaxial side. Legume 32–47 × 3–4.5 mm, 7–9 seeds, linear, slightly falcate at the apex, acuminate, pendulous at the inflorescence rachis, valves brown, coriaceous, protruding margins, densely yellow sericeous. Seeds ca. 3.1 × 2.6 mm, ovate, testa black, elliptical hilum, slightly protruding, excentric ( Fig. 3 ).

Additional specimens examined:— ARGENTINA. MISIONES: Apóstoles, a camino de Puerto Azara , 21 January 1983, E.R. Guaglianone 835 (SI) ; Mártires , 17 February 1945, A. Burkart 15433 (SI) ; San Javier, 23 Km SE de S. Javier, entre Itacaruaré y Sta. María , 2 January 1976, A. Krapovickas 28853 (SI) ; Santo Pipó , December 1950, M. Crovetto 6143 (BAB, SI) . — BRAZIL. RIO GRANDE DO SUL: Giruá, Granja Sodal , 6 November 1964, K. Hagelund 2695 (ICN) ; Santo Ângelo , beira da lavoura, 11 December 1974, L. Arzivenco s.n. (ICN044486) ; locality absent, 1835, M. Isabelle 433 (P). — PARAGUAY. ALTO PARANÁ: Estancia Santa Elena, 19 October 1990, C.G. Marmori 1817 (CTES). AMAMBAY: Chiriguelo, 9 December 1997, A. Schinini 33457 (CTES). CAAGUAZÚ, Caaguazú, east of Caaguazú , 28 December 1994, E.M. Zardini 42105 (BAB, MO, PY), in viciniis Caaguazú, 15 January 1907, E. Hassler 9248 (BM, G, F, K, P) ; Palomares +- 50 Km NW Itakyry, 5 November 1990, G.C. Marmori 1871 (CTES), camino Itakyry a Curuguaty , 10 October 1995, A. Schinini 30020 (CTES) ; Guairá, Pâturages d’Itaugu , près de Villa-Rica, 17 April 1876, Balansa 1051 (K, P) .

Habitat and distribution: —This species occurs in Argentina, Brazil (Rio Grande do Sul) and Paraguay, particularly in open formation of the Paraná Forest province, such as shrubby or grassy formations, between 120–420 m a.s.l ( Fig. 4 ).

Comments: — Macroptilium rubidum was often confused with M. monophyllum due to similarities such as unifoliolate leaves, peduncular bracts forming two tufts at the base, and small buds and fruits. However, M. rubidum can be distinguished by having both unifoliolate and trifoliolate leaves on the same stem, petioles 1.5–4.4 cm, leaflets under 7.6 cm long, a soft ferruginous indumentum, and falcate fruits. In contrast, M. monophyllum consistently has unifoliolate leaves, petioles longer than 4 cm, larger leaflets (5.3–17.5 cm long), pubescent indumentum of erect and rigid trichomes, and straight fruits. Additionally, the species differ in their geographical distribution and ecological preferences. Macroptilium rubidum is found in temperate regions of southern South America ( Paraguay, Argentina, and adjacent Rio Grande do Sul, Brazil) within the Paraná Forest province, while M. monophyllum occurs in savanna vegetation of the Central Brazilian and Bolivian Cerrado and the Gran Sabana of Venezuela and Colombia, often associated with flooded and rocky areas.

Specimens of M. rubidum have often been misidentified as M. erythroloma due to their shared dense indumentum on the leaflets and small fruits. However, M. erythroloma can be clearly differentiated by its climbing habit, shorter trichomes, consistently trifoliate leaves and falcate fruits. A key distinguishing feature is the presence of a fascicle of long linear bracts located just above the base of the peduncle, which is absent in M. rubidum .

Taxonomic notes: —When describing P. rufus, Micheli (1883) considered it distinct from P. monophyllus based on the presence of reddish indumentum on the type specimen (Balansa 1841), attributing the epithet ‘rufus’ to the species (from the Latin rufo = red).

Chodat & Hassler (1904) proposed new infraspecific taxa for P. monophyllus , namely P. monophyllus f. brevipetiolata Chod. & Hassler and P. monophyllus var. paraguariensis Chod. & Hassler. However , we were unable to identify any distinguishing character between these and P. monophyllus , and thus consider them synonymous with M. rubidum .

Hassler (1923) treated P. rufus within a broader circumscription and recognised three varieties and two forms. Phaseolus monophyllus var. unifoliolatus Hassler (1923: 448) and P. monophyllus f. typicus Hassler (1923: 448) are considered here as part of the variation of M. monophyllum . The other taxa recognised by Hassler (1923) are regarded here as synonyms of M. rubidum : P. monophyllus var. unifoliolatus f. paraguariensis Hassler (1923: 449) , characterised by unifoliate leaves with petioles shorter than 15 mm; P. monophyllus var. intermedius Hassler (1923: 449) , with more basal unifoliate leaves and upper leaves trifoliate; and P. monophyllus var. rufus (Micheli) Hassler (1923: 449) , with all leaves trifoliate and reddish indumentum ( Fig. 1 ).

Macroptilium is classified into three sections ( Lackey 1983). Macroptilium rubidum exhibits a combination of characters from two of these sections: unifoliate leaves, characteristic of the section Monophyllum , and flowers smaller than 8 mm long, an ovary with fewer than 7 ovules, and small basal bracts on the peduncle, which are characteristic of the section Microcochle . Piper (1926) considered P. rubidus to belong to the section Macroptilium . Thus, the analysis of the morphology of this species indicates that the boundaries between the sections of Macroptilium need to be reviewed.

Figures

FIGURE 1. Timeline of taxa involving Phaseolus rubidus.

FIGURE 3. Macroptilium rubidum. A. Habit; B. Seed; C. Legume; D. Calyx opened out, upper surface; E. Standard petal, inner surface; F. Wing petals; G. Keel petals; H. Androecium; I. Gynoecium. (A: Hassler 4932; B–C: Croveto 6143; D–I: Hagelund 2695). Illustrated by Kleber Soares.

FIGURE 4. Distribution map of Macroptilium rubidum and M. monophyllum, using biogeographical province of Morrone et al. (2022). Abbreviation of countries AR: Argentina, BR: Brazil, BO: Bolívia, CL: Chile, CO: Colombia, EC: Ecuador, GF: French Guyana, GY: Guyana, PE: Peru, PY: Paraguay, SU: Suriname, UR: Uruguay, VE: Venezuela.