Indigofera sousae Rzed. & R. Grether, 2018

Rzedowski, Jerzy & Grether, Rosaura, 2018, Two new species of the genus Indigofera (Papilionoideae, Leguminosae) from central Mexico, Phytotaxa 372 (4), pp. 256-262 : 257-259

Indigofera sousae Rzed. & R. Grether , sp. nov. ( Fig.1 )

Frutex ca. 1 m altus; folia 7–9 cm longa, stipulis 4–6.5 mm longis, foliolis (9–)11–13 ellipticis ad oblongis 11–22 mm longis, 4–8 mm latis, utrinque strigosis; racemi spiciformes densi ad 10 cm longi, pedicellis 1–1.5 mm longis, floribus ascendentibus; calyx 4–5 mm longus segmentis ad 2.5 mm longis valde inaequalibus; corolla brunneo-rubra 7–8 mm longa; fructus lineares ascendentes 2.5–4 cm longi, 3–4 mm lati, strigosi; semina 8–12 cubiformia 2–3 mm longa griseo-nigrescentia.

Type:— MÉXICO. Michoacán: municipio de Churintzio: Cerro Zináparo, 3.5 km al SE de Churintzio, 20º07’N, 102º02’W, selva baja caducifolia, 29 August 1992 (fl, fr), I. Trejo 2543 (holotype MEXU).

Shrubs ca. 1 m high, densely branched; branches strigose with dolabriform trichomes, glabrescent, purplish-brown; leaves 7–9 cm long, stipules subulate, 4–6.5 mm long, persistent, petioles 1.2–1.5 cm long, leaflets (9–)11–13, elliptic to oblong, opposite, 11–20(–22) mm long, 4–8 mm wide, acute to rounded and mucronate at apex, cuneate at base, membranous, densely strigose, with dolabriform trichomes and glaucous on both surfaces, petiolules 1.5–2 mm long, stipels subulate to triangular, 0.4–1 mm long; inflorescences in spiciform racemes, dense with numerous flowers, axis strigose, up to 10 cm long in flower and 14 cm long in fruit, frequently longer than leaves, pedicels 1–1.5 mm long, flowers ascendent; calyx campanulate, 4–5 mm long, segments 1.5–2.5 mm long, narrowly triangular, of unequal length, strigose outside, persistent in fruit; corolla 7–8 mm long, reddish-brown when dry, standard 7–8 mm long, 4.5–5 mm wide, elliptic, sessile, base attenuate, strigose on abaxial surface, wings 5.5–6 mm long, ca. 1.5 mm wide, glabrous, keel almost as long as standard, sparsely strigose on abaxial surface, its petals 6–6.5 mm long, ca. 1.5 mm wide, fused in upper portion, with spur at midpoint ca. 1 mm long, and basal portion free, claw ca. 1 mm long; stamens 6–7 mm long, anthers basifixed, ca. 1 mm long, mucronate; ovary ca. 4 mm long, strigose, style curved, glabrous, stigma capitate; fruits maturing simultaneously with leaves, linear, biconvex, ascending, straight to slightly curved, 2.5–4 cm long, 3–4 mm wide, blunt but apiculate at apex, valves brown, with prominent venation, margins ochre when ripe, strigose with dolabriform trichomes, endocarp papery, mottled, forming false cross septa; seeds (6–)8–12, cuboid, 2–3 mm long, 1.5–2.2 mm wide, 1.5–2 mm thick, dark gray.

Discussion: —The new species resembles I. constricta Rydberg (1923: 145) in its flowers and ascending fruits, in the elliptic to oblong leaflets, strigose on both surfaces, and the strigose calyx, as well as in the habitat in tropical deciduous forest. However, I. constricta var. constricta extends to tropical subdeciduous forests at low altitudes, while I. constricta var. deorum McVaugh (1987: 540) occurs in cloud forests, at elevations of ca. 1000 m. Table 1 indicates the main differences between these two species. Indigofera constricta var. deorum needs further study to determine its status at the infraspecific or specific rank (McVaugh 1987, Lievens 1992).

On the basis of the many flowered racemes, the short pedicels, the long and narrowly triangular calyx segments, the linear, biconvex pods with (6–)8–12 seeds, this new species is assigned to sect. Tetragonocarpae Wight & Arn. (1834: 203), which has been recognised in the preliminary infrageneric treatment of Indigofera by Schrire (1995: 228); in that treatment, sect. Mucronatae Rydberg (1923: 138), including I. constricta , was placed in the synonymy of sect. Tetragonocarpae.

Habitat: — Indigofera sousae is known only from the type locality and seems to represent a narrow endemism in northwestern Michoacán. Concerning the elevation of the locality of I. sousae , it is important to mention that the label of the type specimen indicates 440 m. However, this should be considered a mistake, since the town of Churintzio is located at about 1800 m and the summit of Cerro Zináparo attains 2300 m.

Phenology: —The plant has been collected with flowers and fruits in August.

Etymology: —The name of the species is dedicated,in sincere posthumous homage,to the extensive accomplishments of Dr. Mario Sousa Sánchez, an outstanding Mexican specialist in the study of the family Leguminosae . His work in this area of science transcends botanical knowledge of this country reaching global dimensions.

Figures

FIGURE 1. Indigofera sousae. A. Flowering branch and rachis with fruits. B. Leaflet, adaxial and abaxial views. C. Calyx. D. Standard, abaxial view. E. Wings. F. Keel, abaxial view. G. Androecium. H. Gynoecium and vexillary stamen. I. Legume with persistent calyx. J. Seed, ventral view. K. Seed, dorsal view. A–K drawn from I. Trejo 2543 (MEXU). Illustration by Anabel Duarte.