Stelis rostriformis Zambrano & Solano, 2018

Romero, Bosco Javier Zambrano & Solano, Rodolfo, 2018, A new species and a new combination in Stelis (Orchidaceae: Pleurothallidinae) from Ecuador, Phytotaxa 376 (4), pp. 177-184 : 181-183

Stelis rostriformis Zambrano & Solano sp. nov. Figs. 1–3 .

Species haec Stelis gargantua Pridgeon & M.W.Chase similis sed sepalo dorsali ovato-elliptico, obtuso, marginibus crenulata , trinervia , petalis obovato-spathulatis, uninervia , labello ovato, columna breviore, rostello elongato differt.

Type:— ECUADOR. El Oro: Cantón Piñas, sector Curitejo , 1300 m, 20 November 2007, B. Zambrano 429 (Holotype in QCNE!; isotype in QCNE! [in spirit]) .

Epiphytic, caespitose herb, up to 60 cm tall. Roots slender, terete, flexuous, whitish, 1.0 mm diameter. Rhizome cylindrical, 5.0 mm long between adjacent stems, covered by 1–2 imbricate, chartaceous, persistent sheaths. Stem slightly ancipitous, unifoliate, 12–37 cm long, 4.0–6.0 mm in diameter, formed by 2 internodes, subtended by 3–4 tubular, imbricate, persistent, chartaceous sheaths, 6.0– 15 cm long, 0.7–15 mm in diameter (14–30 mm when extended), with an annulus near the apex of the distal internode. Leaf shorter than the stem, coriaceous, slightly fleshy, sessile, oblong-elliptic to elliptic, obtuse to widely rounded, emarginated at the apex, cuneate at its base, 13–24 × 7.0– 12 cm. Inflorescence arising from the annulus of the stem, up to 15 simultaneously developed and erect racemes, 20–25 cm long including a slender peduncle, which is covered by 3–4, tubular, imbricate, chartaceous, persistent bracts, 1.0–6.0 mm long, 1.0 mm diameter, enclosed at the base by a spathaceous, conduplicate, persistent, chartaceous bract, 15–25 mm long, 6.0– 10 mm when extended. Floral bract obliquely tubular, acute, persistent, scarious, ca. 1.0– 1.5 mm, 2.0 mm when extended. Flowers small, more or less extended, producing a slightly fetid odor, the sepals and petals light-yellow, lip and column cream, anther yellow-white. Ovary arching, cylindrical, longitudinal sulcate, 0.9–1.0 mm long, 0.4–0.5 mm in diameter, articulated to a terete pedicel, broadened at the apex, 1.8–2.0 mm long, 0.3 mm diameter. Sepals membranous, translucent, glabrous, crenulate along their margins, 3-nerved; dorsal sepal slightly concave, ovate-elliptic, obtuse, reflexed towards the apex, 2.2–2.5 × 1.3–1.5 mm; lateral sepals united almost 1/3 at their base, oblong-ovate or oblong-elliptic, obtuse, convex and slightly reflexed towards the apex, 2.3–2.5 × 1.3–1.5 mm. Petals membranous, porrect, slightly concave, obovate-spathulate, rounded, entire along the margins, 1-nerved, 1.2–1.4 × 0.8–0.9 mm. Lip fleshy, entire, arching in lateral view, ovate, rounded, truncate at the base, articulate at the apex of the foot column, 3-nerved, 1.4–1.5 × 1.0– 1.1 mm, with a longitudinally cleft in the apical half of the lamina; the lateral margins entire, rounded, united almost 1/3 at their base and forming an U. Column short, erect, subterete, 1.0 mm long, 0.4 mm diameter, with a downward robust foot, 0.5 mm long, bulbous at its apex. Stigma consisting into a subapical cleft; rostellum apical, rostrate, laminar, 0.4–0.5 mm long. Anther apical, obovate, glandular-papillose, 0.3–0.4 × 0.3–0.4 mm. Pollinarium ca. 0.4 mm long, with 2 pollinia clavate, serous, yellowish, attached to a tiny drop viscidium. Capsule not seen.

Distribution and habitat: —Up to now Stelis rostriformis is only known from two localities (Curitejo and Lomas Pata Grande) from El Oro province, southwestern Ecuador ( Fig. 3 ). The plant grows as an epiphyte on tree branches of Miconia sp. , on a thick layer of moss, in environments of semi-deciduous montane forests.

Phenology: —In culture, Stelis rostriformis flowers between May and June.

Etymology: —The specific epithet is derived from the Latin rostrum, “beak”, and forma “shape”, in reference to the long and projected rostellum.

Additional specimens: — ECUADOR. El Oro: Cantón Piñas, between Curitejo and Lomas Pata Grande, 1550 m, 13 February 2017, Zambrano 1858 (QCNE).

Comments: —The species most closely related to the new taxon is the Colombian Stelis gargantua , which can be distinguished by its elliptic-ovate, shortly petiolate leaves (vs. oblong-elliptic, sessile), oblong-ovate, marginally ciliate dorsal sepal (vs. ovate-elliptic, marginally crenulate), longer, 3-nerved, and obovate petals (2.25 mm vs. 1.2–1.4 mm, 1-nerved, obovate-spathulate), oblong, trilobated lip (vs. ovate, entire), and longer column foot (0.8 mm vs. 0.5 mm) (Luer 1996, Luer 1998).

Other species similar to S. rostriformis are S. batillacea , S. cyathiflora , and S. galeata . The Ecuadorian and Colombian Stelis batillacea is different by its long petiolate leaves (vs. sessile), obovate dorsal sepal (vs. ovate-elliptic), oblong-obovate petals (vs. obovate-spathulate), elliptic lip with a callous (vs. ovate, without callus), and shorter rostellum (0.2 mm vs. 0.4–0.5 mm) (Luer 1976, Luer 1998). Stelis cyathiflora , from Ecuador, Peru and Bolivia can be distinguished from S. rostriformis by its smaller reproductive plants (25 cm vs. 60 cm), shortly petiolate leaves (vs. sessile), flowers rose with purple (vs. light-yellow), longer dorsal sepal (8.0 mm vs. 2.2–2.5 mm), elliptic-obovate, 3-nerved petals (vs. obovate-spathulate, 1-nerved), oblong obovate lip with lateral and transverse calli (vs. ovate, longitudinally cleft in the center) ( Schweinfurth 1951, Luer 1998).

Finally, the North and South Andean S. galeata differs by having ovate, long petiolate leaves (vs. oblong-elliptic, sessile), ovate, marginally ciliate dorsal sepal (vs. ovate-elliptic, marginally crenulate), longer, oblong-lanceolate petals (≤ 4.0 mm vs. 1.2–1.4 mm, obovate-spathulate), oblong-obovate lip with a callus (vs. ovate, without callus) and longer column foot (0.7 mm vs. 0.5 mm) (Lindley 1845, Luer 1998). Table 1 shows a summary of the morphological characters among the species mentioned above.

Conservation status: —This species is rare because it has not been found in other sites besides the type locality, and it is necessary to consider it as restricted endemic. Stelis rostriformis is present in remnant forests disturbed by human activities (Curtitejo and Lomas Pata Grande), where the populations exhibit low densities (2–3 plants per phorophyte). Furthermore, they are out of protected areas; therefore, the conservation of this species would depend on ensuring the quality of its habitat in order to maintain the viability of its populations.

Additional Notes: —A new name in Stelis , for a species previously assigned to Crocodeilanthe and Pleurothallis subgenus Crocodeilanthe Luer (1986: 34) , is suggested here.

Stelis sagittata Zambrano & Solano nom. nov.

Replacement name: Pleurothallis jamesonii Lindley (1835: t. 1797).

Synonyms: Humboltia jamesonii (Lindl.) Kuntze (1891: 667) ; Crocodeilanthe jamesonii (Lindl.) Luer (2004: 256) .

Etymology: —The specific epithet is derived from the Latin sagittatus, “arrow-head”, in reference to the lip form.

Comments: —The combination of Pleurothallis jamesonii in Stelis proposed by Pridgeon & Chase (2001), Stelis jamesonii Pridgeon & Chase (2001: 264) , proved be illegitimate because the earlier existence of Stelis jamesonii Lindley (1834: 11) , thus requiring the new name proposed here.

Figures

FIGURE 1. Stelis rostriformis Zambrano & Solano. A. Habit. B. Flower, lateral view. C. Flower dissection. D. Lip, ventral and dorsal views. E. Pedicel, ovary and column, lateral view. Drawn by B.J. Zambrano based on the holotype.

FIGURE 2. Stelis rostriformis Zambrano & Solano. A. Habit. B. Apex of the leaf. C. Detail of the spathaceous bract and inflorescences. D. Inflorescence segment with flower, frontal view. E. Detail of the floral bracts. F. Flower dissection. G. Detail of the dorsal sepal. H. Detail of the lateral sepals. I. Detail of the petal. J. Lip and detail of the abaxial surface of the lip. K. Pedicel, ovary, column and lip, lateral view. L. Detail of the column, anther cap, rostellum and foot, lateral view. M. Anther cap and pollinarium. Plate by B.J. Zambrano based on B. Zambrano 1858.

FIGURE 3. Known locality for Stelis rostriformis in Southwestern Ecuador. Map by B.J. Zambrano.