Brongniartia variabilis Dorado, R. Cruz-Durán & R. Bustamante, 2022

Dorado, Óscar, Cruz-Durán, Ramiro & García, Rubí Bustamante, 2022, Two new closely related species of Brongniartia (Fabaceae, Faboideae) from the Sierra Madre del Sur in Guerrero, México, Phytotaxa 544 (1), pp. 1-10 : 6-7

Brongniartia variabilis Dorado, R. Cruz-Durán & R. Bustamante , sp. nov. Fig. 3.

Brongniartia variabilis is similar to B. alvarezii but differs from it by the petals pink or pale pink, to salmon (in older herbarium flowers); standard 6.3–6.9 × 8.5–11.1 mm; wing petals 7.1–7.6 × 3.4–3.9 mm; keel petals 7.3–7.7 mm.

Type:— MÉXICO. Guerrero: Municipio de Chilpancingo , Carretera Mazatlán-Petaquillas 3.6 km después de la entrada a Mazatlán, siguiendo 500 m por camino de terracería. Al sur del poblado de Petaquillas, 17.460356, -99.470164, 16 junio 2017, Ó. Dorado. 9960, G. Cuevas, J. de Jesús - Almonte, A. Florentino & J. López (holotype: MEXU, FCME, isotype RSA) .

Shrub to 1.5 m tall with one to several main stems, branches beige, light brown or grayish; branchlets hirtellous, velutinous to tomentulose, hairs 0.8–1.6 mm, erect or sometimes retrorse, brown and white. Stipules (0.5–)0.9–2(–2.8) × (0.3–)0.4–1(–1.8) cm, obliquely oblong to obliquely lanceolate, commonly deciduous in older leaves, venation commonly conspicuous, on mature and more glabrous stipules; texture rather thin, glabrous or pubescent with strigose or sericeous hairs, margin sometimes revolute, lower lobe slightly developed and forming a -135° to -180° angle with the longitudinal axis of the stipule, the edge of the stipule adjacent to the petiolate excurvate or rarely incurvate, apex acute. Leaves (3.7–) 6–15 cm, glabrous or pubescent with white or brown hairs; petiole (0.4–) 0.8–1.6 cm, often markedly striate, hirtellous or glabrous; rachis (1.2–) 3–12 cm, with (7–)9–7 opposite or subopposite leaflets, hirtellous or glabrous; stipels 0.5–2.4 × 0.2–0.3 mm at the base, yellowish red, thick and stout or thin and slender; leaflets 1.1–3(–4.3) × 0.4–1.3(–1.4) cm, petiolule (0.6–) 1–3 mm, hirtellous or glabrous, lamina oblong or rarely elliptic or lanceolate, texture rather thin, paler on the abaxial surface, strigulose or sericeous with hair 0.3–0.6 mm, sometimes brownish, commonly denser on the abaxial surface, sometimes glabrous, base rounded or sometimes obtuse, apex rounded, with a mucro 0.2–1(–2) cm, margin revolute. Flowers borne solitary or pair at base of leafy nodes; peduncles 1.2–2.6 cm, erect, hirtellous with either white or brown hairs, more densely distributed adjacent to the bracteoles, or sometimes glabrous; bracteoles 0.3–0.5 × 0.1–0.2 mm, triangular to subulate, persistent or not, normally opposite, beige or yellowish; calyx 0.9-1.4 × 0.35–0.5 cm, campanulate, strigose, with white hairs, or sometimes glabrous, two vexillar lobes 7–8.5 × 2.2–2.5 mm (both lobes), free 1/5 of their length, lateral lobes 5.3–8 × 1.3–2 mm, lanceolate to linear-lanceolate, carinal lobe 4–7 × 1–2.1 mm, linear–lanceolate to subulate; petals pink or pale pink (specially the standard and wings petals), to salmon (in older herbarium flowers); standard 6.3–6.9 × 8.5–11.1 mm, macula yellowishgreen with outline dark red, claw 4–4.6 mm, ca. 130°-180°, blade of the standard orbiculate and non-auriculate at the base; wing petals 7.1–7.6 × 3.4–3.9 mm, claw 2.3–2.8 mm, obliquely oblong, with an extended auricula almost as long as the claw, forming a 25° to 30° angle with the claw; keel petals 0.73–0.77 × 0.4–0.49 cm, claw 2–2.4 mm, mostly yellowish, being pink or pale pink towards the ventral edge; semilunate, ventral edge of the keel plane, claw 3–3.2 × 0.5–0.8 mm, auricula of the keel forming a 45° to 50° angle with the claw; androecium 1.5 cm, anthers 0.8 mm; ovary 1.6 cm, with 3(–4) ovules, with a blackish annular disk 1 mm at the base of the ovary, style 6 mm. Fruit 3.8–4.5(–5.7) × 1.5–2.1 cm, obovate or rarely oblong, stipe 4.5–6 mm, mucro 1.5–3.3 cm, one seed maturing per fruit. Seeds 9 × 4.9 mm, 2 mm thick, ellipsoidal, brown mottled with black, or dark brown.

Distribution: — B rongniartia variabilis is presently known only from the vicinity of Chilpancingo, Guerrero. The elevation ranges from 1366 to 1850 m above sea level.

Habitat and phenology:— Brongniartia variabilis is a species found on slopes of Oak forest with Quercus L. (1753: 994) and Juniperus L. (1753: 1038) and open temperate forest, with species commonly also found in sclerophyllous woodland such as Astianthus viminalis (Kunth) Baill. (1888: 44) , Rhus chondroloma Standl. (1936: 164) , Ipomoea arborescens (Humb. & Bonpl. ex Willd.) G. Don (1838: 267) , Bursera glabrifolia (Kunth) Engl. (1896: 251) , B. copallifera , Bocconia arborea S. Watson (141: 1890), Brahea dulcis , Pithecellobium dulce (Roxb.) Benth. (1844: 44) , Dodonaea viscosa (L.) Jacq. (1760: 19), Spondias purpurea L. (1762: 613), Heliocarpus terebinthinaceus (DC.) Hochr. (1914: 125) , among others, and species of Ptelea L. (1753: 118). The flowering and fruiting period is mostly in the beginning of the rainy season (May and June).

Additional material examined: — Mexico: Guerrero: Municipality Chilpancingo: slope of Culebrado Hill, W of Chilpancingo, 30 May 1967, Chavelas Es-1804 (MEXU); Along Chilpancingo, 9 Jun. 1974, Sanders 74064 (MICH, TX); Salto de Valadez, 1 km N of Tejocote, 3 August 1978, T. German & O. Téllez 910 (MEXU); Amojileca, 8 km N de Chilpancingo, 15 July 1979, A. Delgado & J. García 1072 (MEXU); 5 km W of Amojileca, along dirt road Chilpancingo-Amojileca, 7 May 1982, D. Rodríguez & E. Martínez 43 (MEXU, RSA); 4.5 km W of Chilpancingo by the dirt road toward Amojileca, 5 January 1988, Ó. Dorado & R. Torres 1845 (MEXU, RSA); 1 km W of Chilpancingo, above Colonia Zapata, 11 July 1988, Ó. Dorado, S. Zona, R. Torres & E. Sandoval 1733, 1734 , 1734b (MEXU, RSA); 6 km al oeste de Amojileca siguiendo la carretera en dirección a Omiltemi, 17.569417, -99.609594, 11 July 2014, Dorado 9265, G. Cuevas, J. M. de Jesús-Almonte, E. Gacía, E. Leyva (MEXU); Carretera Mazatlán-Petaquillas 3.6 km después de la entrada a Mazatlán, siguiendo 500 m por camino de terracería. Al sur del poblado de Petaquillas, 17.460356, -99.470164, 16 June 2017, Ó. Dorado 9961, G. Cuevas, J. M. de Jesús-Almonte, A. Florentino & J. López (MEXU, FCME); 3 km al Suroeste de Petaquillas, por la carretera Petaquillas-Mazatlán, 5 km después de Petaquillas, después 500 m por camino de terracería, 17.460422, -99.470128, 1 July 2017, Ó. Dorado 9969, 9970, 9971, 9972, 9973, 9974, 9975, 9976, G. Cuevas, A. Florentino, J. López, M. López & F. Ortiz . (MEXU, FCME). Municipality Tixtla de Guerrero, Tixtla Chilapa, 16 June 1946, Miranda 3977 (MEXU); sobre la carretera Tixtla-Chilapa, a la altura del poblado Plan de Guerrero, 17.591200, -99.356743, 24 June 2020, Ó. Dorado 10427, 10428, 10429, G. Cuevas, A. Florentino, J. Florentino & E. Leyva (MEXU, FCME).

Specific epithet: —As its specific epithet denotes, this is a species with an extensive range of variation in both vegetative and floral features. The pubescence of the branches varies from tomentulose, hirtellous or sericeous to completely glabrous. The color of the hairs is either white or brown, sometimes drying to a yellowish color in herbarium specimens. Most of the hairs are erect, but on one collection (Dorado & Torres 1845), a conspicuous, retrorse pubescence occurs. The pubescence of the leaflets is mostly strigose, but some specimens have a sericeous layers of hairs, particularly on abaxial surface. It is worth to mention that leaflets of some of the collections are complete glabrous (from either young or mature leaves). The number of leaflets is also variable; some leaves bear only 7 leaflets while most of them range from 11 to 17. The stipules are both persistent and not uncommonly deciduous in some individuals of the same population. The calyx can be either strigose with white or brown hairs, or completely glabrous. The size of the calyx is also variable, ranging from 9 mm to 14 mm long. I have been seen most of the abovementioned variation in a single population. We have observed that the density of pubescence of vegetative structures in several species of the genus varies seasonally, according to the age of the structure, being very dense when the leaves are still young; once the leaves become older, the density of pubescence diminishes, and the leaves may become completely glabrous. However, variation in the type of pubescence seen in B. variabilis is not very common in the genus.

Discussion: —These two species, B. alvarezii and B. variabilis have morphological similarities: i) small flowers, ii) a standard reflexed ca. 130° to 240° blade of the standard. Besides these morphological features, they are also found in temperate forest in the Balsas River Basin, sometimes in ecotone with seasonally dry tropical forests woodlands (SDTFW, sensu DRYFLOR 2016) or sometimes-sclerophyllous woodlands. Therefore, we consider that these couple of species are the closest relative of each other, probably been closer to Brongniartia abbottiae , an endemic species from the vicinity of Taxco, Guerrero (Table 2).