Erythrostemon sousanus J.L. Contreras, S. Sotuyo & G.P. Lewis, 2017

Contreras-Jiménez, José Luis, Sotuyo, Solange, Calvillo-Canadell, Laura & Lewis, Gwilym P., 2017, Erythrostemon sousanus (Leguminosae: Caesalpinioideae), a new species from the Río Papagayo Basin in Guerrero, México, Phytotaxa 308 (2), pp. 289-294 : 292-293

Erythrostemon sousanus J.L. Contreras, S. Sotuyo & G.P. Lewis , sp. nov. ( Figures 1 and 2 )

Type:— MÉXICO. Guerrero: 2 km east of Petaquillas, J. L. Contreras 2810 (holotype FCME).

Diagnosis:— Erythrostemon sousanus is morphologically similar to Erythrostemon mexicanus (A. Gray) E. Gagnon & G.P. Lewis , but has densely pubescent fruits and inflorescences, the petals have confluent disciform glands towards the claw which cover the whole abaxial surface of the petal blade. Erythrostemon sousanus leaves have more pairs of pinnae and the pinnae have more pairs of leaflets, and the flowers, fruits and seeds are larger than in E. mexicanus . Table 1.

in mm except for legume length in cm. Based on Herbarium material.

Erythrostemon sousanus similis E. mexicano fructu pubescenti et inflorescentia penitus floribus inclusis; petalis unguem versus cum glandulis confluentibus disciformibus totam superficiem abaxialem tegentibus; foliis cum pluribus pinnis et foliolis binatim, fructibus et seminibus maioribus quam in E. mexicano ; sicut in E. mexicano pubescentia solum ad articulum florescentiae vel glabra; calyce in superficie interiore pubescenti, petalis glabris, quamquam superficies dorsalis glandulas stipitatas in dimidio basali et secus marginem unguis praebet; fructibus circa suturam glabris vel modice pubescentibus. ( Table 1).

Shrubs 1–3 m tall; bark green with abundant lenticels. Leaves bipinnate, 15.5–28.5 cm long, glabrous; stipules caducous (not seen); petioles 5.5–10.5 cm long; rachis 7.5–21 cm long; pinnae in (6–) 9–11 (–13) pairs per leaf, each pinna (2.3–) 4–9.5 (–11) cm long; leaflets in (4–) 5–7 (–8) pairs per pinna, elliptic, oblong–elliptic, ovate to obovate (1.4–) 2–3 × (0.4–) 0.9–1.5 (–1.8) cm, apex obtuse, rounded or retuse, margin entire, revolute, with punctate glands, base oblique, glabrous, secondary veins brochidodromous with fifth-order veins polygonal-reticulate. Inflorescence axillary, racemose, 25–45 cm long, peduncle thick (0.1–0.2 mm), striate, densely dark pubescent; bracts ovate, long acuminate, 9–12 × 2.5 mm, scarious, yellow-orange, pubescent on both surfaces; pedicels 6–11.5 mm long, articulated near the calyx base, dark pubescent; calyx green, its tube obliquely obconic, 8.3–8.5 × 3.5 mm, striate, pubescent, adaxial sepals oblong–ovate, 8.5–9.5 × 5.5–7 mm, apex obtuse to rounded, the margin serrulate, ciliate, lateral sepals oblong–ovate, 9–9.5 × 5.3–6 mm, apex obtuse, margin serrulate, ciliate, abaxial sepal ovate, cymbiform, 10.5–12.5 × 7.5–8.5 mm, apex rounded, margin erose, ciliate, all sepals pubescent on both surfaces; petals yellow, median petal narrowly-ovate, 8.5–9.5 × 8.5–11 mm, apex rounded, base subcordate, petal lamina forming an angle of 90–105º with the claw, with red punctations, abaxial surface densely covered by green discoid glands, claw 5.5–7.5 mm long, incurved, glabrous on its adaxial surface, densely villose on its lower margin, glandular-stipitate on the abaxial surface with a pubescent fleshy membrane over the claw articulation, upper lateral petals ovate, 9–12.5 × 10.8–13.5 mm, apex rounded, base subcordate, abaxial surface covered by disciform green glands, these confluent around the 3–4 mm claw, pubescent on the adaxial surface, glandular-stipitate on the abaxial surface, lower lateral petals ovate, 9.5–12.5 × 8.2–10.5 mm, apex and base rounded, abaxial surface with green disciform glands, claw 3.5–4.5 mm long, puberulent on the adaxial surface, the margin glandular-stipitate on the abaxial surface; stamen filaments green, curved, 10–15.5 mm long, villose for ⅔ to ⅘ their length; anthers oblong-ovate, 1.4–2 × 0.8–1.2 mm, dark greenish; pollen grains spheroidal, prolate, tricolporate, syncolporate, semitectate, reticulate, pores lolongate; ovary sessile, curved, 6–6.5 mm long, style curved, 9–12 mm long, villose from base to half its length; ovules 3–4 per ovary; stigma terminal, obliquely cupuliform, ciliate. Fruit falcate, laterally compressed, 8–8.3 × 2–2.2 cm, valves yellow, subligneous, densely pubescent, elastically dehiscent. Seeds 1–3(–4) per fruit, ovate, laterally compressed, 12–13 × 9–10 × 2 mm, shiny, yellowish green.

Selected specimens examined:— MÉXICO. Guerrero: Municipio de Chilpancingo , camino a las grutas de Juxtlahuaca, 30/05/1976, A. Delgado 195 et al. ( CHAPA, MEXU) ; on the road from Chilpancingo to Mochitlán, 4 km from main Chilpancingo-Acapulco road, 09/02/1992, D. J. MacQueen et al. 427 ( EAP, FHO, K, MEXU) ; 4 km to the east of Chilpancingo on the road Juxtlahuaca-Colotipa, 26/05/2001, J. L. Contreras et al. 7197, 7198 ( MEXU) .

Habitat:— Seasonally dry tropical forest on limestone; 1000–1200 m.

Distribution and phenology:— Known only from the Río Papagayo basin (late Oligocene-Eocene) around Petaquillas in Guerrero, México. Flowering from December to May and in fruit from January to July.

Etymology:— The species is dedicated to Mario Sousa Sánchez who recently passed away (1940–2017). Friend, teacher, pillar of botany in México and researcher at the Universidad Nacional Autónoma de México, he was an expert on the legume genus Lonchocarpus and in floristic and vegetation studies of legumes (e.g. Sousa 2012; Sousa et al. 2001). Dr. Sousa, a devoted defender of herbaria and plant taxonomy, described up to 100 species new to science ( Sousa et al. 2014), principally legumes. He was also instrumental in promoting botanical exploration throughout México and Central America as a leader of expeditions and general editor of Flora Mesoamericana. He was Head of Mexico’s Herbario Nacional from 1975 to 1985 and 1994 to 2003. We are indebted to him for all he taught us and for having ensured the continuing success of Mexico’s Herbario Nacional.

Conservation assessment:— We propose a conservation assessment of Vulnerable [VU (B1b-iii)] for Erythrostemon sousanus , in accordance with IUCN (2001) categories and criteria. The extent of occurrence (EOO) of E. sousanus is estimated to be below the 20,000 km 2 upper limit for Vulnerable status under criterion B1, but its area of occupancy (AOO) is estimated to be less than 10 km 2 (the limit for Endangered status under criterion B2). The species is currently known from fragmented vegetation in the state of Guerrero. The preferred habitat of the species is potentially threatened by settlements, forestry and agricultural activities, as well as by environmental problems associated with settler ʼ s armed uprisings.

Figures

FIGURE 1. Erythrostemon sousanus. a. bipinnate leaf; b inflorescence; c flower lateral view; d median (standard) petal; e upper lateral petal; f lower lateral petal; g gynoecium; h stamens; i calyx; j developing infructescence; k fruit. Drawn from Contreras-Jiménez 7198 (a–j) and 7197 (k) (MEXU) by Albino Luna.

FIGURE 2. Different features of Erythrostemon sousanus. a part of inflorescence with buds and open flowers; b bracts at inflorescence apex; c flower bud showing the cymbiform, serrulate lower sepal and the articulated pedicel; d flowers front view; e flower lateral view; f fruit; g cleared leaflet with brochidodromous secondary veins; h pollen grain in polar view; i stigma. Photos a–f taken by J.L. Contreras- Jiménez.