Maxillaria tenebrosa Zambrano & Solano, 2016

Romero, Bosco Javier Zambrano & Solano-Gomez, Rodolfo, 2016, Maxillaria tenebrosa, a new species in the Maxillaria variabilis group (Orchidaceae: Maxillariinae) from Southwestern Ecuador, Phytotaxa 289 (3), pp. 247-255 : 248-254

Maxillaria tenebrosa Zambrano & Solano sp. nov. Figs. 1 and 2

Similar to Maxillaria variabilis , from which is distinguished by their pendent habit, inflorescences produced from the mature pseudobulb, porrect petals, and entire lip.

Type:— ECUADOR. El Oro: Cantón Piñas, filo el Trigal, 1200 m, 8 May 2007, Zambrano B. 101 (Holotype in QCNE; isotype in Herb. J. Zambrano [in spirit]) .

Plant epiphytic, pendent, rhizomatous, 25–30 cm tall. Rhizome pendulous, cylindrical, 2–3 cm long between adjacent pseudobulbs, covered by conduplicate, distichous, overlapping, chartaceous, persistent, acute sheaths. Roots flexuous, slender, whitish, 1 mm diameter. Pseudobulbs ellipsoid, distichous, ancipitous, light green, smooth when young, longitudinally striated when mature, 3.0– 4.5 cm long, 1.8–2.0 cm wide, apically 1-foliate (rarely 2-foliate), subtended by 3–6 foliaceous distichous, conduplicate, persistent, chartaceous, and overlapping sheaths, sometimes purple spotted. Leaf sessile, elliptic to lanceolate-ensiform, obtuse, slightly coriaceous, arching, conduplicate at the base, obliquely bilobed at the apex, light green, sometimes purple spotted on abaxial surface in young leaves, slightly blurred in the mature ones, 16–20 × 1.2–2.0 cm. Inflorescence from the mature pseudobulb, 1–3 per pseudobulb; peduncle erect, cylindrical, 15 mm long, 1.5 mm diameter, with 3–4 overlapping bracts similar to the floral ones, 8–10 × 2.0– 2.5 mm (5 mm when extended). Floral bracts conduplicate, acute, carinate, scarious, 6–7 mm long. Inflorescence one-flowered, bell-like, more or less open, producing a slightly fetid odor; the sepals, petals, and lip dark purple, the column light purple and lustrous on ventral surface, the anther and pollinia dark purple. Ovary pedicellate, slightly arching, cylindrical, longitudinal sulcate, 20 mm long, 2 mm diameter. Dorsal sepal fleshy, oblong-oblanceolate, obtuse, slightly concave, shortly apiculate, slightly recurved at apex, 5–7-nerved, 13.0 × 4.5–5.0 mm; lateral sepal fleshy, obliquely oblonglanceolate, acute, shortly apiculate, slightly reflexed at the apices, slightly concave at the base, 5–7-nerved, 14.0 × 5.0 mm. Petals fleshy, porrect, obliquely oblanceolate, acute, shortly apiculate, slightly recurved at apex, slightly concave, erose along the margins, 5-nerved, 12.0 × 3.5 mm. Lip entire, fleshy, arching, conduplicate, articulate at the base of the column foot, the blade oval-elliptic when extended, sub-rounded, retuse, pilose-papillose at apex, 7–8-nerved, abruptly attenuate at base, 13.0 × 7.5 mm; the lateral margins erose, erect and undulate up to the middle third; with a callus on the lower middle of the lip, prominent, thickened, elevated, subquadrate, lustrous. Column slender, arching, semiterete, slightly 2-winged at the apex, 8.5–9.0 mm long, 2.5–3.0 mm wide at the stigma level, with a downward foot, ca. 3 mm long, light purple and dark purple spotted; clinandrium marginally ciliolate. Anther apical, ovoid, galeate, pilose-papillose, ca. 2.3 × 2.3 mm. Pollinarium formed by 4 pollinia, in two subequal pairs, longitudinal ovoid, 2.0 × 1.5 mm, attached to a semilunar viscidium with the arms downwards. Capsule narrowly ellipsoid, with a persistent perianth, 2.5 cm long (3 cm including the remnant column), ca. 5 mm diameter.

Distribution and habitat: —Up to now Maxillaria tenebrosa is only known from two localities from El Oro province, southwestern Ecuador. This species grow between 600 and 1,300 m in elevation, in semi-deciduous premontane and semi-deciduous montane forests ( Fig. 3 ). The plant grows as an epiphyte on tree branches of Ficus sp. and Mauria sp.

Floral biology: —In culture, M. tenebrosa has flowered from March to December. The dark purple flowers, fringed sepals and petals, landing platform formed by the lip, short hairs at apex of lip and column, and fetid odor emitted by the flowers suggests that this species has a sapromyophylous pollination syndrome ( van der Pijl 1966, Argue 2012). Flower scent is more intense from 10:00 and 15:00; then it decreases and again it is intensified in the morning the next day. This pattern in the production of the floral aroma might regulate pollinator visitation, which could be attracted looking for feeding or egg-deposition sites in the flower.

Etymology: —The specific epithet is from the Latin tenebrosus, “dark”, in reference to the flower color.

Additional specimens:— ECUADOR. El Oro: Cantón Piñas, parroquia Capiro, near sector Antoniopamba , 856 m, 2 June 2014, Zambrano B. 1390 (Herb. J. Zambrano, cultivated in Orquiecuador & Gloxinias) ; parroquia Capiro, on the way up to Loma del Guayacan , 840 m, 2 June 2014, Zambrano B. 1408 (Herb. J. Zambrano, cultivated in Orquiecuador & Gloxinias) ; parroquia Capiro, sector Conchicola , 650 m, 21 September 2015, Zambrano. B. 1698 (Herb. J. Zambrano, cultivated in Orquiecuador & Gloxinias) .

Comments: — Maxillaria tenebrosa is a member of the M. variabilis group or Maxillaria sect. Erectae , where the most similar species are: M. acervata , M. caespitifica , M. caucae , M. costaricensis , M. dichaeoides , M. ponerantha , M. procurrens , M. variabilis , and M. xanthorhoda . The new taxon is most similar with the Mesoamerican M. variabilis , but it is different by its procumbent habit (vs. pendent), inflorescences produced from the developing pseudobulb (vs. from the mature one), flowers yellow or yellow with red stain (vs. dark purple), petals strongly recurved (vs. porrect), and lip lightly 3-lobed (vs. entire) ( Bateman 1837, Jiménez et al. 1998). On the other hand, M. variabilis has not been reported for Colombia and Peru ( Bennett & Christenson 1993, 1995, 1998, 2001, Dodson 2004, Trujillo 2014), so the geographic disjunction among the southernmost populations of this species and that from M. tenebrosa allows recognizing them as different taxa.

and M. xanthorhoda .

The South Central American M. caucae , originally described as M. parvula ( Schlechter 1924: 176) , can be distinguished by its erect habit (vs. pendent), ovoid pseudobulbs (vs. ellipsoid), oblong-elliptic leaves (vs. elliptic to lanceolate-ensiform), petals slightly recurved at the apex and 3-veined (vs. porrect, 5-veined), and ovary ≤ 10 mm long including the pedicel (vs. ≥ 15 mm) ( Garay 1967). Among other similar Maxillaria , the Central American and South American M. caespitifica is different by its caespitose habit (vs. rhizomatic), lanceolate leaves (vs. elliptic to lanceolate-ensiform), yellow or greenish yellow flowers (vs. dark purple), sepals 5–7 mm long (vs. 13–14 mm), strongly recurved petals (vs. porrect), and lip <8 mm long (vs. ≥ 10 mm). The south Central American and South American M. ponerantha differs by its erect habit (vs. pendent), shorter leaves (2.5–8 cm vs. 16–20 cm), yellow-cream with red stain flowers (vs. dark purple), petals ≤ 7 mm, 3–4-veined (vs. 12 mm, 5-veined). Another similar species is M. costaricensis , restricted to Costa Rica and Panama, it differs from M. tenebrosa by its fusiform to cylindric pseudobulbs (vs. ellipsoid), green to cream or rose flowers (vs. dark purple), and slightly 3-lobed lip (vs. entire) ( Atwood & Mora de Retana 1999). The South Central American M. acervata different by its shorter leaves (1.5–6 cm vs. 16–20 cm), green to white flowers, red stained lip (vs. dark purple), marginally entire petals (vs. erose), and lip ≤ 10 mm, marginally entire and rounded at apex, (vs. ≥ 10 mm, erose, and retuse) ( Reichenbach 1855). The North Andean M. dichaeoides differs by having oblong-elliptic leaves (vs. elliptic to lanceolate-ensiform), smaller, marginally entire and 3-veined petals (7 mm vs. 12 mm, marginally erose and 5-veined), lip <8 mm long, without a callus (vs. ≥ 10 mm, with a lustrous callus) ( Bennett & Christenson 2009). The South American M. procurrens is distinguished from M. tenebrosa by its procumbent habit (vs. pendent), leaves with apex mucronate (vs. non-mucronate), marginally entire petals (vs. erose), lip with a rounded apex (vs. retuse) ( Lindley 1845). Finally, M. xanthorhoda , endemic to Peru, differs by its rhizome of 5–6 cm long between adjacent pseudobulbs (vs. 2–3 cm long), elliptic leaves (vs. elliptic to lanceolate-ensiform), pink with red spots flowers (vs. dark purple), strongly recurved petals (vs. porrect), and lip with an emarginated apex (vs. retuse) ( Schlechter 1918, Bennett & Christenson 1998). Table 1 present a summary of the differences among the species mentioned above.

Conservation status: —Not evaluated, but it is desirable to consider this species in a risk category to ensure its protection. Maxillaria tenebrosa has a very restricted geographical distribution. The only known localities are in remnant forest disturbed by human activities, where the populations are at risk as a result of deforestation and their low densities (1–3 plants per phorophyte). Furthermore, due to the fragmentation process that affects the habitat of the known populations (Filo de Trigal and Capiro), they are isolated, little interconnected among them, out of protected areas and so far, the species has not been found in other similar forests of the region.

Figures

FIGURE 1. Maxillaria tenebrosa Zambrano & Solano. A. Habit. B. Flower, lateral view. C. flower dissection. D. Ovary, lip and column, lateral view. E. Clinandrium margin, ventral view. F.Anther. G. Pollinarium. Drawn by B.J. Zambrano based on the holotype.

FIGURE 2. Maxillaria tenebrosa Zambrano & Solano. A. Habit. B.Apex. C. Inflorescences. D. Flower, lateral view. E. Flower dissection. F.Detail of the petal (500x). G. Detail of the lip (500x). H. Pedicel, ovary, column and lip, lateral view. I. Anther cap and pollinarium. J. Column apex, pollinarium and anther cap, lateral view. K. Detail of the clinandrium margin, lateral and ventral view (500x). Plate by B.J. Zambrano based on cultivated specimens.

FIGURE 3. Known localities for Maxillaria tenebrosa in Southwestern Ecuador. Map by B.J. Zambrano.