Acianthera bilobulata Zambrano & Solano, 2021

Romero, Bosco Javier Zambrano & Solano, Rodolfo, 2021, Acianthera bilobulata (Orchidaceae: Pleurothallidinae), a new species from Southwestern Ecuador, Phytotaxa 490 (2), pp. 159-171 : 160-170

Acianthera bilobulata Zambrano & Solano sp. nov. Figs. 1–3 .

Species haec Acianthera pubescens (Lindley) Pridgeon & M.W.Chase similis sed foliis elliptico-lanceolatis, sepalo dorsali oblongooblanceolato, petalis acutis, marginibus erosis, labello oblongo, obtuso, lobis lateralibus oblongis, rotundatis differt.

Type:— ECUADOR. El Oro: Cantón Piñas, parroquia Capiro , sector Los Amarillos , 1110 m, 28 October 2019, Zambrano B . 2429 (holotype QCNE; isotype QCNE) .

Epiphytic herb, pendent, caespitose, up to 22 cm long. Roots slender, flexuous, 1.0 mm diameter. Rhizome cylindrical, 5.0–10.0 mm long between adjacent secondary stems, with 2–3 internodes, covered with imbricate, chartaceous, persistent sheaths, 5.0–12.0 mm × 3.0–4.0 mm (6.0–8.0 mm when spread out). Secondary stem unifoliate, terete at the base but then laterally compressed upwards, slightly arching, channeled, 4.5–12.0 cm long, 2.0–3.0 mm in diameter, subtended by 2 tubular, imbricate, persistent, chartaceous sheaths, 30.0–45.0 mm long, 2.5–3.0 mm in diameter. Leaf fleshy, sessile, lanceolate to elliptic-lanceolate, obtuse, coriaceous, slightly decurrent to the secondary stem at the base, 6.0–10.0 × 2.5–3.5 cm. Inflorescence shorter than the leaf, arising from the apex of the secondary stems, a simultaneously flowered raceme, 3.5–5.5 cm long including the peduncle, enclosed at the base by a spathaceous, conduplicate, persistent, chartaceous bract, 10.0–16.5 × 4.0–5.0 mm when spread out; peduncle terete, 10.0–20.0 mm long, 1.5 mm in diameter, smooth to minutely pubescent, covered at the base by 2–3 tubular, obtuse to sub-acute, persistent, conduplicate, scarious bract, 2.0–3.0 × 1.5 mm; rachis terete, 15–30 mm long, 0.8–1.3 mm in diameter; floral bract, acute, persistent, scarious, 1.0–1.5 × 3.0 mm when spread out. Ovary pubescent, slightly arching, cylindrical, longitudinally sulcate, 1.7–2.0 mm long, 1.0– 1.2 mm in diameter, articulate to a terete pedicel of 1.0– 1.5 mm long, 0.8–1.2 mm diameter. Flowers small, bilabiate, producing a slightly fetid odor, the sepals yellow-cream with red-purple spots, petals white-translucent with red-purple at the base, lip and column white-yellow with red-purple spots, the anther white with red-purple. Sepals fleshy, densely pubescent on the adaxial surface, papillose, minutely spiculate on the abaxial one, ciliate; dorsal sepal concave but incurved at the apex, oblong-oblanceolate, obtuse, minutely apiculate, 3-nerved, 6.0–7.5 × 1.8–2.0 mm; lateral sepals united into a concave synsepal for almost one third of their length, ovate, strongly bifid at the apex, 6-nerved, 6.0–7.0 × 5.5–6.0 mm, each apex acute. Petals slightly fleshy, porrect, unguiculate, rhombic-spathulate, acute, erose marginally, 1-nerved, 2.3–2.5 × 1.5–1.7 mm. Lip 3-lobed, fleshy, porrect in natural position, slightly arched, articulate at the column base, oblong, obtuse, minutely apiculate, marginally entire, truncate and with two auriculate lobes at the concave base, with a transverse callus, covered by a translucent, viscous-substance on the adaxial surface, 3.0–3.5 × 1.3–1.5 mm; lateral lobes translucent, erect, oblong, rounded, 0.4–0.5 × 0.35–0.4 mm; mid-lobe panduriform, provided with two parallel and sub-marginal calli extended from the lateral lobes, forming an oblong groove on the middle, 1.8–2.0 × 1.2–1.3 mm, channeled among the calli. Column short, arching, sub-terete, winged at the apex, ventrally channeled, 2.4–2.5 mm long and 0.9–1.0 mm in diameter, with a foot of 1.0– 1.3 mm long; clinandrium slightly projecting and covering the anther base, flabellate, minutely denticulate at apex and erose along its margin; stigma ventral, concave, covered by a viscous substance; rostellum ventral, ovate. Anther incumbent, obovate, glandular-papillose, 0.6 × 0.6 mm; pollinarium 0.3 mm long, formed by 2 pollinia, yellow, obovate, serous, attached to a granulose caudicles. Capsule not seen.

Distribution and habitat: — Acianthera bilobulata is only known from El Oro province in southwestern Ecuador, at about 1100 m in elevation ( Fig. 3 ). The plant grows as an epiphyte on shrub branches of Ficus sp. , in semi-deciduous premontane forests. The new species is present in remnant forest disturbed by human activities, where it occurs in low densities (1–3 plants per phorophyte). Furthermore, they are outside protected areas, so the conservation of this species would depend on ensuring the persistence of its habitat. To date this species has not been found in other localities from El Oro province, and it is necessary to consider it as steno-endemic.

Phenology: —In culture A. bilobulata flowered between July and August.

Etymology: —The specific epithet is from the Latin bi “with two” and lobules “lobes”, in reference to the lateral lobes near the base of the lip.

Paratype:— ECUADOR. El Oro: Cantón Piñas, parroquia Capiro, sector Los Amarillos , 1110 m, 28 October 2019, Zambrano B . s.n. (QCNE).

Comments: —The new taxon is similar to Acianthera breedlovei , A. henrici , A. majakoluckae , and A. pubescens . The most similar species is A. pubescens , which differs from A. bilobulata in the oblong-lanceolate to oblong-elliptic leaves suffused with purple (vs. elliptic-lanceolate, green leaves), flowers suffused and striped with dull purple (vs. yellow-cream flowers suffused with red-purple), a longer and broader dorsal sepal, with red-purple stripes on the veins (8.0–13.0 × 2.5–3.25 mm vs. 6.0–7.5 × 1.8–2.0 mm, without red purple stripes on the veins), obtuse petals with denticulate margins (vs. acute, margins erose), a larger ovate lip with minutely serrate margins and a rounded apex (3.5–4.0 × 2.0– 2.2 mm vs. 3.0–3.5 × 1.3–1.5 mm, oblong with entire margins and an obtuse, minute apiculate apex), and falcate, sub-acute lateral lobes (vs. straight, rounded lobes) ( Fig. 4D , 5 , 8A ) ( Lindley 1836, Hooker 1841).

Populations determined as Acianthera pubescens in Ecuador (Loja ( Fig. 8B , 9 ), Zamora-Chinchipe, Morona- Santiago), and Peru (San Martin, Junín, Pasco, Huancavelica) are restricted along the Eastern Cordillera ( Luer 2004, Damián et al. 2018), where they are located on the transition zone of evergreen premontane and semi-deciduous cloud premontane forests, the precipitation is about 1500–2000 mm a year ( Sierra 1999). Instead, populations of A. bilobulata occur in the semi-deciduous premontane forests, a “dry ecosystem”, at the interior of the Amotape-Huancabamba zone ( Weigend 2004), the estimated precipitation is about 1000 mm a year. This geographic disjunction, in two distinctive biogeographic areas, suggests different environmental or ecological preferences for both species, so that they can be recognized as separate taxa.

The delimitation of Acianthera pubescens is problematic because the name, and that of its basionym Pleurothallis pubescens Lindley (1836: 355) , has been applied to different species ranging from eastern Mexico to Uruguay and northern Argentina, including the Antilles (Soto & Solano 2003, Soto et al. 2003, Solano 2015). Several phenetically similar species have been described from Brazil, Mexico, Puerto Rico, and Venezuela, but the differences between them remain unclear in most cases, and their names have been frequently grouped into the A. pubescens synonymy.

According to Luer (2004), the type of Pleurothallis pubescens is found in K, but it has not been possible to locate it. A hand-copy made by L.A. Garay from a type illustration is kept at AMES (Barcode no. 00074658) ( Fig. 4D ) and it shows a plant similar to that illustrated as Pleurothallis picta Hooker (1841 : pl. 3897) ( Fig. 5 ); both names were based on Mexican specimens. Specimens from Puebla (Eslava s.n. [OAX, photo!]) and Veracruz (Bourgeau s.n. [P!], Castro s.n. [OAX, photo!], Diguet s.n. [P!], Purpus 2142 [AMES!], Morales s.n. [OAX photo!], Purpus 6397 [AMES!], Purpus sub Oestlund 6732 [AMES]!) in Mexico and determined as A. pubescens ( Solano 2015) , morphologically correspond to those that appear in the above-mentioned drawing and plate, as well as the types of P. bourgeaui Kraenzlin (1921: 15) , P. mandibularis Kraenzlin (1920: 169) , P. polystachya Richard & Galeotti (1845: 16) , and P. vittata Lindley (1838: 73) , which are now synonymized with A. pubescens . Types specimens for other names assigned to A. pubescens , according to Luer (2004) and Damián et al. (2018), come from Southern Brazil: Parana: Dusén 11571, 11573 (syntypes of P. porphyrantha Kraenzlin 1921: 10–11 ); Rio de Janeiro: Smith s.n. (holotype of P. smithiana Lindley 1843: 57–58 ) ( Cogniaux 1893, Fig. 7I ), Barbosa s.n. (holotype of P. janeirensis Barbosa Rodrigues 1882: 29–30 ); Rio Grande do Soul: Barbosa s.n. (holotype of P. rio-grandensis Barbosa Rodrigues 1882: 28 ) ( Cogniaux 1893, Fig. 7 II); Venezuela: Trujillo: Wagener 31 (holotype of P. truxillensis Reichenbach 1854: 25 ) ( Dunsterville & Garay 1959, Fig. 6 ), Wagener s.n. (holotype of P. bufonis Klotzsch 1854: 225–226 ), and Puerto Rico: Adjuntas, Sintesis s.n. (neotype of P. coriacea Bello 1883: 116 ). But these specimens differ in the shape of the leaves, the length of the inflorescence with respect to the leaf, the size and color of their flowers, and in the shape of petals and lip. Also, there is no type specimen that has been collected and described from a plant in the Andes from Colombia, Ecuador or Peru.

It is likely that Acianthera pubescens is restricted to Mexico and possibly northern Central America, while similar plants from South America would represent different taxa. Future morphological and molecular studies are required to establish the limits among the different taxa through its wide distribution range. In northern Mesoamerica, two species have been segregated from A. pubescens , A. breedlovei , distributed from Chiapas ( Mexico) to Nicaragua, and A. majakoluckae , distributed in Oaxaca, Chiapas ( Mexico), and probably in Guatemala. The Mesoamerican A. breedlovei , differs from A. bilobulata by its lanceolate, narrower leaves (1.0–2.0 cm vs. 2.5–3.5 cm, elliptic-lanceolate leaves), much more open, greenish-yellow to olive-green with red purple spots flowers (angle between dorsal sepal and synsepal greater than 90º vs. less than 90º, yellow-cream flowers with red-purple spots), longer and narrower ovate synsepal (5.0–6.0 × 2.8–3.5 mm vs. 6.0–7.0 × 5.5–6.0 mm), slightly falcate petals (vs. straight), obovate, rounded lip with erose margins (vs. oblong, obtuse and marginally entire), and sub-quadrate lateral lobes (vs. oblong lobes) ( Fig. 4A ) (Soto et al. 2003). On the other hand, A. majakoluckae differs in the elliptic to ovate-elliptic, fleshy-thickened leaves (vs. elliptic-lanceolate and fleshy leaves), longer synsepal (7.0– 10 mm vs. 6.0–7.0 mm) and petals (2.5–3.2 mm vs. 2.3–2.5 mm), greater, elliptic and rounded lip (3.5–4.0 × 1.8–2.2 mm vs. 3.0–3.5 × 1.3–1.5 mm, oblong and obtuse lip), and oblong-triangular lateral lobes (vs. oblong lobes) ( Fig. 4C ) (Soto & Solano 2003).

Finally, among the Ecuadorian Acianthera , the most similar species is A. henrici , but it is differs in the erect plants (vs. pendent), elliptic, acute leaves (vs. elliptic-lanceolate, obtuse leaves), flowers dark purple (vs. yellow-cream flowers suffused with red-purple), obovate, minutely denticulate petals (vs. rhombic-spathulate, erose), and an entire, verrucose lip (vs. 3-lobed, non-verrucose lip) ( Fig. 4B ) ( Schlechter 1921, Luer 2004).

Figures

FIGURE 1. Acianthera bilobulata Zambrano & Solano. A. Habit. B. Flower, lateral view. C. Flower dissection and detail of the abaxial surface of the lateral sepal. D. Pedicel, ovary and column, lateral view. Drawn by B.J. Zambrano based on the holotype.

FIGURE 2. Acianthera bilobulata Zambrano & Solano. A. Habit. B. Detail of the spathaceous bract and the inflorescence. C. Flower, lateral view. D. Flower dissection. E. Detail of the abaxial surface of the lateral sepal. F. Pedicel, ovary and column, lateral view. G. Detail of the column. H. Lip, frontal, 3/4, and lateral view. I. Anther cap and pollinarium. Plate by B.J. Zambrano based on the holotype.

FIGURE 3. Known locality for Acianthera bilobulata in Southwestern Ecuador. Map by B.J. Zambrano.

FIGURE 4. Illustrations of: A. Acianthera breedlovei. B. Acianthera henrici. C. Acianthera majakoluckae D. Acianthera pubescens. A, C by R. Solano; B from Luer 2004 (Courtesy of Missouri Botanic Gardens Press). D by L.A. Garay, reproduction with permission of the Oak Ames Orchid Herbarium, Harvard University.

FIGURE 5. Reproduction of drawing of Tabula 3897 published in Botanical Magazine (Hooker 1841) as Pleurothallis picta.

FIGURE 6. Illustration of Pleurothallis truxillensis. Reproduction with permission of the Oak Ames Orchid Herbarium, Harvard University.

FIGURE 7. Reproduction of drawings of Tabula 107. I. (1−6) Pleurothallis smithiana, II. (1−6) Pleurothallis rio-grandensis, published in Flora Brasiliensis (Cogniaux 1893).

FIGURE 8. A. Specimen of Acianthera pubescens from Veracruz, Mexico (Courtesy of J. Morales-Linares). B. Specimen assigned to A. pubescens from Loja, Vilcabamba, Ecuador. Photograph by B.J. Zambrano.

FIGURE 9. Specimen labeled A. pubescens from Loja, Vilcabamba. Plate by B.J. Zambrano based on Zambrano s.n.