Bletia mixtecana Salazar & Chávez-Rendón, 2016

Salazar, Gerardo A., Chávez-Rendón, César, Ávila, Alejandro De & Jiménez-Machorro, Rolando, 2016, Floral similarity and vegetative divergence in a new species of Bletia (Orchidaceae) from Mexico, Phytotaxa 275 (2), pp. 112-126 : 120-123

Bletia mixtecana Salazar & Chávez-Rendón , sp. nov.

Vegetatively it differs from all other species of Bletia in its ovoid pseudobulbs and its restriction to gypsum outcrops along ravines and steep slopes. Florally it is similar to B. parkinsonii , but differs from the latter in the absence of a distinct retrorse mentum at the base of the floral tube; labellum marginally adnate to the column at base; proximal portion of the labellum provided with a central channel formed by prominent, thickened veins; labellum disc provided with 5 − 7 prominent, entire keels, these coloured deep magenta on their proximal two-thirds, irregularly dentate, undulate and cream-white above; column devoid of distinct ventral auricles near the middle.

Type: — MEXICO. Oaxaca: distrito Huajuapan, municipio Santo Domingo Tonalá, La Cuchara, 1538 m elev., collected 4 September 2002, pressed in cultivation 8 April 2006, Chávez-Rendón et al. 5598 R (holotype MEXU, isotypes IEB!, SERO!).

Terrestrial herb, 15 − 32 cm in height including the inflorescence. Roots simple, terete, flexuous, dull white to pale brown, glabrous to pubescent-lanuginose, 1.5 − 2.0 mm in diameter. Pseudobulbs epigeous, ovoid, slightly compressed laterally, consisting of 6 − 7 internodes, when young completely concealed by sheaths, when old naked, green with reddish-brown nodes, smooth, longitudinally sulcate, 3.4 − 6 cm long, 1.0 − 2.3 cm in diameter. Leaves deciduous, shedding at maturity of the pseudobulb, absent at flowering time, when present 7 − 8, progressively larger toward the apex of the pseudobulb, the imbricating sheaths of the 4 − 5 distalmost leaves forming a pseudostem up to 3.5 cm long; leaf blades plicate, green, articulate to the sheaths that conceal the pseudobulb, linear to ensiform or the lowermost one sometimes lanceolate, long-acuminate at apex, truncate and channelled at base, 9-veined, 4 − 24 cm long, 0.8 − 1.4 cm wide; sheaths conspicuous, concealing completely the newly developed pseudobulb, tight, papery-fibrous, whitish, eventually disintegrating (after about ca. 4 years), up to 4 cm long and 2 cm wide. Inflorescence racemose, 1 − 2 per pseudobulb, up to 23 cm long, arising from the nodes on the distal two-thirds of the mature pseudobulb, erect; peduncle slender, terete, rigid, ca. 11 cm long and 0.9 mm in diameter, with 4 − 5 internodes and an equal number of tight to loose, scarious bracts up to 7 mm long; raceme lax, ca. 10 cm long, rachis glabrous, 0.25 − 0.8 mm in diameter, slightly flexuous, producing 5 − 10 flowers in succession. Floral bracts thin, scarious, glabrous, covering less than one-fifth to one-fourth of the ovary, triangular-ovate or ovate, sometimes that of the lowermost flower tubular, apex acute or obtuse, apiculate, 5 − 12-veined, (0.6 −) 2.4 − 4.4 mm long, 1 − 2 mm wide. Ovary glabrous, ascending, slightly arcuate, subterete, 6-sulcate on the distal two-thirds, gently tapering and obscurely twisting towards the base, pale green to purplish-red with three green ribs, 10.0 − 16.5 mm long, ca. 1 mm in diameter near the apex. Flowers resupinate, widely open in warm, sunny weather but the sepals and petals barely opening in cloudy weather; floral segments inconspicuously connate at base for up to 0.5 mm, bearing sparse, minute idioblasts apparently containing crystals. Sepals completely magenta or externally white with magenta suffusion on margin and internally magenta except for the white base, bearing at base 5 main veins that branch above; lateral sepals free except as noted above, variably spreading, obliquely oblong-oblanceolate, slightly recurved near the acute apex, obscurely keeled dorsally, 15.5 − 20.0 mm long, 4.0 − 4.5 mm wide; dorsal sepal oblanceolate, recurved, 15.0 − 19.3 mm long, 2.9 − 4.1 mm wide. Petals homogeneously magenta, free or fused basally to the labellum for 0.7 − 2.0 mm (degree of adnation variable even among flowers of the same inflorescence), bearing at the base 3 main veins that branch above, obliquely oblanceolate or oblanceolate-spathulate, minutely crenate-lacerate and slightly undulate on the distal one-fourth to one-third, acute to obtuse, 15 − 20 mm long, 2.9 − 5.0 mm wide. Labellum white on the proximal half with the lateral lobes and the margins of midlobe magenta, the centre of the midlobe white; base adnate to the column for 1.8 − 2.4 mm, otherwise free, obscurely three-lobed above the middle, in natural position with the lateral margins below the lateral lobes embracing the column, 16.8 − 19.5 mm total length, 9.4-9.5 mm wide across the lateral lobes when spread out; lateral lobes semiorbicular, somewhat divergent, rounded, erose and slightly undulate, protruding 1 − 2 mm at apex; midlobe obcordate to cuneate − obcordate, 5.0 − 6.5 mm long, 5.8 − 6.7 mm wide, deeply emarginate at apex, the resulting lobules obliquely ovate-flabellate, ruffled, margins erose and undulate, apex shortly apiculate (sometimes the apicule inconspicuous); base bearing 5 main veins that branch profusely above (the three central veins nearly reach the apex of the midlobe); disc provided with 5 − 7 prominent keels, these entire and deep magenta on their proximal two-thirds, irregularly dentate, undulate and cream-white above, sometimes a few more lateral veins slightly thickened but not distinctly keeled, base of the labellum channelled inside the short tube resulting from its partial adnation to the column, the channel formed by the basal portions of the keels that run at each side of the central one (the last one does not reach the base); no nectar is produced. Column elongate, slightly arching, white near the base and magenta above, ventrally flat with thin, slightly prominent margins, more noticeably so below the middle, 10.8 − 11.5 mm long including the short, inconspicuous column foot, 2 mm wide near the apex; anther incumbent, semi-globose, versatile, with slightly prominent apical margin, 8-celled, ca. 1.5 mm long and wide; pollinia 8, yellow, laterally compressed, with granulose caudicles; rostellum laminar, semiorbicular, reflexed, provided on its adaxial surface (facing the stigma) with a lunate viscarium. Stigma semiorbicular, concave, with margins slightly raised, covered by a shiny, transparent fluid in fresh condition. Capsules not seen.

Distribution and ecology:— Bletia mixtecana is known only from two populations distant from one another c. 76 air kilometres, both within the Mixtec region in the Sierra Madre del Sur, state of Oaxaca. The plants live on gypsum in banks along ravines and on steep slopes. At the type locality (La Cuchara; Fig. 1A–C ) the dominant vegetation is tropical deciduous forest with Acaciella angustissima ( Miller 1768: Mimosa no. 19) Britton & Rose (1928: 100), Agave aff. angustifolia Haworth (1812: 72) , Brahea dulcis ( Kunth 1816: 300) Martius (1838: 244) , Bursera mirandae Toledo (1984: 441) , Euphorbia aff. rossiana Pax (1910: 162) , Fouquieria ochoterenae Miranda (1942: 458) , Neobuxbaumia mezcalaensis ( Bravo 1932: 378) Backeberg (1941: 3) , Opuntia Tournefort ex Miller (1754 : Opuntia ) sp., Plumeria rubra Linnaeus (1753a: 209) , and the orchids Bletia parkinsonii , Cyrtopodium macrobulbon ( Lexarza 1825: 42) Romero-González & Carnevali (1999: 331) , Dichromanthus cinnabarinus ( Lexarza 1825: 3) Garay (1982: 314) subsp. galeottianus ( Schlechter 1918: 432) Soto Arenas & Salazar (in Hágsater & Soto Arenas 2003: xii) and Ponthieva angustipetala Greenwood (1986: 9) . At the other known locality (Cerro Jacaba; Fig. 1D–E ) the steep gypsum slope is covered by a tall scrub of Neobuxbaumia Backeberg (1938: 20) sp. with sparse individuals of Brahea dulcis , Hechtia Klotzsch (1835: 401) sp. and Agave Linnaeus (1753a: 323) sp. , with a sparse herbaceous stratum including Selaginella Palisot de Beauvois (1805: 101) sp. , Begonia Linnaeus (1753b: 1056) sp. , Sedum Linnaeus (1753a: 430) sp. , Pinguicula Linnaeus (1753a: 17) sp. , some grasses and xeromorphic ferns and two further orchid species, Galeoglossum cactorum and an unidentified species of Malaxis Solander ex Swartz (1788: 119) .

Conservation status:— From the small number of known populations (two), the small area that they occupy (less than 1 km 2), the small number of individuals known (a few dozen) and its habitat specificity, this species qualifies as ‘Endangered’ according to the ‘MER-Plantas’ (the method for assessing the risk of extinction for plants established by the relevant Mexican legal norm; SEMARNAT 2010). Likewise, based on IUCN’s red list categories and criteria ( IUCN 2012), B. mixtecana qualifies as ‘Endangered’ because of its area of occupancy estimated to be <500 km 2, less than five known locations and an observed decline in the number of mature individuals, at least at La Cuchara (criteria B2, a(iii)). Nevertheless, the two known populations of B. mixtecana occur on a rough, botanically little-explored area with seemingly extensive spans of potential habitat. It is likely that further exploration will lead to the discovery of additional populations, and its conservation status should be then revised accordingly.

Etymology:— The specific epithet refers to the Mixtec region of Oaxaca, an area to which the new species seems to be restricted.

Additional specimens examined:— MEXICO. Oaxaca: distrito Huajuapan, municipio Santo Domingo Tonalá, paraje Cerro de la Cuchara-Barranca , 1,383 m, 13 January 2009, Hernández & Torres 869 ( MEXU!, SERO!) ; municipio Santo Domingo Tonalá, La Cuchara , 1,518 m, 10 February 2009, Torres & Hernández 910 ( MEXU!) ; distrito Tlaxiaco, municipio San Bartolomé Yucuañe, Cerro Jacaba , 1708 m elev., collected 15 August 2008, pressed in cultivation 17 March 2015, Chávez-Rendón et al. 7421 C ( MEXU!) .

Figures

FIGURE 1. A. Tropical deciduous forest around La Cuchara gypsum mine, type locality of Bletia mixtecana. B. Plant of B. mixtecana growing on a gypsum wall. C. Massive plant on an unstable bank of a ravine, growing alongside Selaginella sp. D. Columnar cactus (Neobuxbaumia sp.) scrub on a gypsum outcrop at Cerro Jacaba, the second known locale for B. mixtecana. E. Plants of B. mixtecana and Selaginella sp. growing at the base of Neobuxbaumia sp. F. Pseudobulb of a plant of B. mixtecana at flowering time during the dry season, after shedding the leaves, showing the base of the inflorescence emerging from a lateral node. G. Inflorescence of the type plant (Chávez- Rendón et al. 5598R). Photographers: César Chávez-Rendón (A−E, G); Gerardo A. Salazar (F).