Acianthera pollardiana Solano, 2015

Gomez, Rodolfo Solano, 2015, A taxonomic synopsis of the Mexican species of Acianthera (Orchidaceae: Pleurothallidinae) including a new species, Phytotaxa 218 (1), pp. 39-60 : 42-43

Acianthera pollardiana Solano sp. nov. ( Figs. 1 − 2 , 5 )

Similar to Acianthera chrysantha ( Lindley 1859: 14) Pridgeon & Chase (2001: 243) , from which is distinguished by their broader leaves, tubular and nearly closed flowers, and fleshy, more lanceolate, five-veined sepals.

Type:— MEXICO. Oaxaca: Distrito Tlaxiaco, Municipio Santiago Yosondúa, paraje La Cueva del ex Presidente, localidad de Cascada la Esmeralda, 1913 m, 16º50’46.1’’ N, 97º34’50.05’’ O, bosque de galeria, 7 October 2014, D. Sandoval 1248 & A. Sandoval (holotype MEXU!).

Epiphyte, erect, short cespitous herb, up to 25 cm tall. Roots flexuous, whitish, ca. 1 mm in diameter. Rhizome short, globose, comprising three internodes. Stem unifoliate, as long as or longer than the leaf, straight or slightly arching, progressively dilated and winged toward the apex, 12 − 14 cm long, ca. 4 mm wide, 8.6 mm thick, comprising two internodes, the proximal shorter than the distal, the distal one conduplicate, covered by tubular, scarious, shedding sheaths. Leaf sessile, fleshy, elliptic to ovate-elliptic, obtuse-rounded, shortly bilobed at apex and with a minute mucro between lobes, 11 − 12.0 × 5 cm. Inflorescence arising from the apex of the stem, racemose, up to 3 cm long; peduncle terete, 7 mm long, 1.2 mm diameter, enclosed by a conduplicate, obtuse, scarious bract, 8 − 9 mm long, with other two overlapping bracts similar to the floral one, 7.2 − 7. 4 mm long; rachis abbreviated, with 4 − 6 successively opening and erect flowers in a fan-like arrangement. Floral bracts obliquely funnel-shaped, obtuse, membranous, greenish yellow, 4 − 5 mm long, overlapping. Flowers with the sepals forming a tube, with a small aperture at apex, 12 − 13 mm tall, 3.5 − 5.3 mm long, 4 − 5 mm wide; sepals, petals, lip, and column, reddish orange, the anther yellow. Ovary stout, subpyramidal, subtriangular in cross-section, greenish yellow, shortly glandular-pubescent, 1 − 1.7 mm long, articled to a terete pedicel of 1.3 − 3 mm long, both covered by the floral bract. Sepals fleshy, glabrous on the adaxial surface, short glandular-pubescent on the abaxial surface, ciliate, involute along the margins; dorsal sepal united to lateral sepals near its base, elliptic to oblanceolate-spatulate, rounded to obtuse, channeled, subcalyptrate at apex, five-veined, 11 − 12 × 3.5 − 4.1 mm; lateral sepals united up to the apex, forming a cymbiform, oval to elliptic, rounded synsepal, shortly retuse at the apex, ten-veined, 10 − 11.6 × 7 − 8 mm. Petals porrect, fleshy, slightly channeled, obovate to ellipticoblanceolate, rounded, slightly attenuated toward the base, serrulated along upper 3/5, three-veined, 2.9 − 4 × 1.4 − 1.8 mm. Lip fleshy, entire, shortly unguiculate; claw short, membranous, trapezoidal, two-auricled at base; disc slightly arching, conduplicate, oblong-lanceolate, obtuse, shortly apiculate, three-veined, 4 − 4.6 × 1.8 mm, with a pair of submarginal, elevated, thickened calli on the middle third, which descends along the basal margins of the lip. Column slightly arching, ventrally channeled, winged, 2.5 − 2.6 × 1 mm, with a concave foot, 1.9 mm long; wings oblong, 0.4 mm tall, slightly erose along the margins, clinandrium projecting, covering the anther, concave, denticulate; stigmatic cavity ventral, subquadrate, viscous; rostellum galeate, ventral. Anther ventral, ovoid, incompletely divided inside by a pair of septa, 0.8 − 0.9 mm long; pollinarium 0.5 − 0.6 mm long, comprising two ovoid, laterally compressed, yellow pollinia, attached to two granulose, flake-like caudicles. Capsule not seen.

Distribution and habitat:—Endemic, known only from the Sierra Madre del Sur of Oaxaca ( Fig. 5 ). This species grows between 2,000 and 2,200 m in elevation, in pine-oak or ravine mesophytic fores, with Taxodium mucronatum Tenore (1853: 355) , Quercus magnoliifolia Née (1801: 268) , Q. pubescens Willdenow (1796: 279) , Fraxinus uhdei ( Wenzig 1883: 182) Lingelsheim (1907: 221) , Gliricidia ehrenbergii ( Schlechtendal 1838: 303) Rydberg (1924: 239) , Litsea glaucescens Kunth (1817:168) , and Randia cookii Standley (1934: 176) , which are surrounded by pine forests at higher sites. The plant is an epiphyte on oak trees like Quercus magnoliifolia .

Phenology:—Flowering from September to October.

Etymology:—The specific name honors the memory of Glenn E. Pollard, who lived in Oaxaca City in the 1960s and 1970s studying Mexican orchids.

Additional specimens: — MEXICO: Oaxaca: Municipality of Santiago Yosondua, Mixteca region , 2000 − 2200 m, secondary vegetation derived from the oak forest, collected June 2001, pressed September 2004, Suárez 2273 ( OAX) ; municipality of Santa Catarina Juquila, road Juquila to Ixpantepec , 29 September 2005, Solano 1297 ( OAX) ; unknown locality, prepared from cultivated specimen at AMO, October 2000 ( AMO) ; unknown locality, Lau s.n. ( AMO [photo]) .

Comments:—Among the Mexican Acianthera , this species is easily recognized according to its stout habit, orange-reddish, elongated and more or less tubular flowers, and its fleshy, five-veined sepals. This species is similar and occasionally sympatric with another Mexican endemic taxon, A. chrysantha , but it can be recognized according to its smaller habit, narrower leaves, shorter bilabiate and more open flowers. The Mesoamerican A. circumplexa ( Lindley1838: 24) Pridgeon & Chase (2001: 243) is also similar, but can be distinguished by prominent abaxially keeled leaves, raceme apparently arising from the foliar blade, and shorter, bilabiate flowers. Although the South American A. aurantiolateritia ( Spegazzini 1916: 132) Pridgeon & Chase (2001: 242) has similar flowers, this plant has lanceolate, narrow leaves, raceme longer than the leaf, several flowers that simultaneously open, and aristate petals.

Acianthera pollardiana is endemic to the Sierra Madre del Sur of Oaxaca,a little explored region with other geographically restricted orchid species whose range extends to the mountains surrounding the Central Valleys of Oaxaca, highlighting the importance of this region as a priority biological conservation area ( Salazar & García-Mendoza 2009, Salazar et al. 2010, Solano 2010). The geographically restricted orchids in this region include Cypripedium molle Lindl. in Bentham (1840: 72), Dichromanthus cinnabarinus subsp. galeottianum Soto Arenas & Salazar in Hágsater & Soto (2003: xii), D. yucundaa Salazar & García-Mendoza (2009: 24) , Galeoglossum cactorum Salazar & Chavez-Rendon in Salazar et al. (2011: 262), Habenaria subauriculata Robinson & Greenman (1896: 34) , Laelia furfuracea Lindley (1839: 26) , and Stelis sotoarenasii Solano (2010: 450) .

Conservation status:—Not evaluated by the IUCN Red List or the Method of Extinction Risk Evaluation for Mexican wild flora and fauna species.This plant is scarcely known and has been collected from few localities, where the populations have seemingly low densities and in some parts of its range the forest is perturbed by itinerant agriculture. However, there is still suitable habitat for this species in unexplored areas in Southern Oaxaca.

Figures

FIGURE 1. Acianthera pollardiana Solano & Soto Arenas. A. Habit. B. Abscision zone between stem and leaf with the inflorescence. C. Floral dissection. D. Ovary, lip and column, lateral view. E. Lip, ventral view. F.Column, ventral view. G. Anther. H. Pollinarium. Drawn by R. Solano based on specimen cultivated without locality data.

FIGURE 2. Acianthera pollardiana, photo by G. Salazar, based on Sandoval & Sandoval 1248.

FIGURE 5. Map showing the known Mexican localities for Acianthera johnsonii, A. majakoluckae, A. obscura, A. pollardiana and A. pubescens.