Stelis guerrerensis Soto Arenas & R.Solano, 2014

Stelis guerrerensis Soto Arenas & R.Solano , sp. nov. ( Figs. 1 View FIGURE 1 , 4A View FIGURE 4 )

Similar to Stelis pachyglossa (Lindl.) Pridgeon & M.W.Chase from which it differs by its smaller and caespitose habit, arching inflorescence, smaller flowers, lateral sepals united with each other to their apices, and distribution.

Type:— MEXICO. Guerrero: municipio Atoyac de Alvarez, El Molote , selva perennifolia de montaña, ca. 1600 m elev., prensado de material cultivado, 18 Sep. 2006, Santiago in Salazar 6739 ( MEXU!) .

Epiphytic, erect, caespitose herbs, up to 50 cm tall including inflorescence. Roots flexuose, whitish, 0.3–0.6 mm in diameter. Rhizome 3–6 cm long between adjacent stems, 3 cm in diameter, covered by scarious sheaths. Stems unifoliate, subterete, formed by two internodes, 4.0– 11.5 cm long, 1.4–1.8 mm in diameter, with an annulus 3.0– 3.5 mm below apex, completely covered by tubular, oblique, obtuse, carinate, overlapping, and scarious sheaths. Leaf elliptic, acute or obtuse, shortly bilobed at apex and with a minute mucro between lobes, 5.0–13.0 × 1.5–4.2 cm; blade conduplicate, pale green on the adaxial surface, grayish green and carinate abaxially, the base attenuate into a conduplicate petiole, 0.7–1.7 mm long. Inflorescence arising from the annulus of stem, racemose, erect, as long as leaf, 6.5-8.5 cm long; peduncle terete, 3.5–4.0 cm long, 0.3–0.4 mm in diameter, green, densely suffused with purple; rachis gradually lengthening at apex, with up to six successively opening flowers, enclosed at base by a conduplicate, triangular, acute, scarious, carinate bract and provided with two other tubular, obtuse bracts, 3.4– 4.5 mm long. Floral bracts tubular, oblique, obtuse, apiculate, 3.4–3.7 mm long. Flowers bilabiate, laterally compressed, 11–12 mm long, 7.5–10 mm wide, sepals and petals greenish yellow to orange, purple along veins, medial lobe of lip yellow-cream, tinged densely with purple, the lateral ones translucent, column yellowish green suffused with dark purple, the foot white, anther yellowish green. Ovary obconic, subtrigonous, green and densely purple-tinged, 3.0– 3.3 mm long, 0.8–1.2 mm in diameter; pedicel subterete-conic, 2.0– 5.6 mm long, 0.5 mm in diameter. Dorsal sepal directed upward and above column, cymbiform, recurved at apex, 12.0 × 4.5–5.5 mm, approximately ovate-lanceolate, acuminate, three-veined, shortly keeled along veins, microscopically ciliate; lateral sepals fully connate into a concave-caliculate, ovate, acute synsepal, shortly bifid at apex, six or sevenveined, two-keeled, microscopically ciliate, 10.0–12.0 × 6.5–7.0 mm. Petals porrect, slightly arching, obliquely obovate, obtuse, thickened at apex, the distal margin involute-subcalitrate and forming a fovea, distally convex, proximally subcuneate, pilose-papillose on adaxial surface, papillose-verrucose toward apex on abaxial surface, three-four-veined, 6.3–6.5 × 3.4–3.5 mm. Lip 8.3–9.0 mm long, 2.4 mm wide, trilobed, lateral lobes basal and embracing column, auricled, erect, retrorse, triangular-ovate, rounded, 1.5 × 2 mm, midlobe much larger than lateral lobes, reflexed to near base, lingulate, rounded, densely glandular-papillose on entire surface, with two parallel and erect keels on adaxial surface extending from lateral lobes up to the middle, channeled among them, distal part (without keels) 4.5 × 2.0– 2.2 mm, straight, apically rounded and thickened, with a callus that extends from the base up to the middle between the lateral lobes, canaliculate, 6.0 × 0.6 mm. Column 2.2–2.6 mm long, 0.8–1.0 mm wide at stigma level, much longer than lip, slightly arching, attenuate towards apex, ventrally channeled, adaxially with margins extended, column foot present, foveolate, papillose, 1.0–1.5 × 0.8 mm, clinandrium projecting, concave, distally incurved, triangular, truncate and emarginate at apex, 0.8 mm long, stigmatic cavity ventral, quadrate-elliptic, viscous, 0.4 × 0.4 mm, rostellum galeate, covering stigma, semi-ovoid, yellow, anther galeate, ventral, truncate and papillose-dentate at apex, incompletely divided inside by a pair of septa, 0.7–0.8 × 0.6-0.7 mm, pollinarium 0.4 mm long, consisting of two obovoid, compressed, yellow pollinia, each 0.4 × 0.25 mm, attached to two granulose, flake-like caudicles, 0.1 mm long. Capsule not seen.

Distribution and habitat: —Endemic to Mexico in the Transverse Volcanic Belt (Temascaltepec area, Mexico State) and Sierra Madre del Sur (Teotepec area, Guerrero), two biogeographic provinces separated by the Balsas Depression ( Fig. 5 View FIGURE 5 ). It grows as an epiphyte in forests of Quercus candicans (Née; Fagaceae ), Alnus jorullensis (Kunth; Betulaceae ), Pinus montezumae (Lamb.; Pinaceae ) and Pinus teocote (Schltdl. & Cham.; Pinaceae ) in the Teotepec area or in oak-pine forest in Temascaltepec area, 1900–2500 m.

Phenology:— Flowering from June to January but mostly June to August.

Etymology:— The specific name refers to the Mexican state where the species was first recorded.

Additional specimens examined: — MEXICO. Guerrero: Municipio General Helidoro Castillo, Puerto de la Piedra Acanalada , 17º26’12” N, 100º12’ W, 1950 m elev., Soto & Salazar sub Laboratorio de Biogeografia 783 ( FCME!) GoogleMaps ; Mexico State: Temascaltepec, camino de terraceria Telpintla a Jesus del Monte, 2.5 km al SW de Jesus del Monte , 19°06’11.8’’, 100°00’5.04’’, 2200 m elev., 25 Septiembre 2009, Lopez-Patiño s.n. ( MEXU! photo) .

Comments:— This taxon appears to be a vicariant of Stelis pachyglossa (Lindley; 1840: 68) Pridgeon & M.W.Chase (2001: 265), a common and widespread species in Mexico and Central America with populations distributed along the Sierra Madre Oriental, trans-isthmic mountains, and both mountain ranges in Chiapas. Furthermore, S. pachyglossa is differentiated by its less caespitose habit, broader leaves, longer inflorescence, and lateral sepals fused into a deeply bifid synsepal. Stelis guerrerensis also differs by its more calyptrate and warty petals on the outer surface and broader callus of the lip.

Conservation status:— Not evaluated by the IUCN Red List or the Method of Evaluation of Extinction Risk for Mexican wild species. Apparently the species is threatened by its restricted distribution (known from only three localities) and locally scarce populations. Moreover, its habitat, formerly abundant in Guerrero, has been severely affected in the last 30 years by the establishment of milpas, coffee plantations, and even poppy crops. Currently, it has virtually disappeared and is limited to canyons and steep mountain slopes. The population in Temascaltepec was recently discovered where the habitat is inaccessible, and up to now it is well preserved (D.R. Szeszko and E. Lopez-Patiño, Tuluca, Comision Nacional Forestal, pers. comm.); the surrounding forests, however, are affected by the construction of farmhouses, logging, agriculture, and quarrying.