Pleurothallis inaudita Zambrano & Solano, 2023

Romero, Bosco Javier Zambrano & Solano, Rodolfo, 2023, Pleurothallis inaudita, an unnoticed new species in Pleurothallidinae (Orchidaceae) from southwestern Ecuador, Phytotaxa 620 (1), pp. 70-78 : 74-76

Pleurothallis inaudita Zambrano & Solano , sp. nov. ( Figures 1–3 ).

Type: — ECUADOR. El Oro: Cantón Atahualpa, sector Daucay-Cerro Azul , 883 m, 01 July 2017, Zambrano B. 1961a (holotype: QCNE!; isotype: QCNE!) .

Species similar to P. imitor , from which differs by its apically long acuminate leaves (vs. apically acute), flowers amber suffused with red-purple (vs. yellow), lanceolate dorsal sepal (vs. ovate), ensiform, acuminate petals, 4.3–4.5 mm long (vs. oblong-subfalcate, acute petals, 9 mm long), ovate-triangular lip with an oblate callus (vs. triangular-sagittate with an oblong callus), and a shorter column (2.0 mm long vs. 0.9–1.2 mm long).

Description: — Epiphytic herb, caespitose, up to 13.0 cm long. Roots slender, flexuous, 0.4–0.6 mm diameter. Rhizome cylindrical, 0.2–0.3 mm long between adjacent secondary stems, with 1–2 internodes each, covered with imbricate, chartaceous, persistent sheaths. Secondary stem unifoliate, terete at the base but then laterally compressed upward, slightly channeled, 2.0–10.0 cm long, 0.5–0.7 mm in diameter, subtended by 2 tubular, imbricate, persistent, chartaceous sheaths, 13.0–22.0 mm long, 1.0–2.0 mm in diameter. Leaf slightly coriaceous, lanceolate when young to elliptic-lanceolate when mature, obtuse and distally long-acuminate, emarginate-mucronate at the apex, sessile, somewhat conduplicate and scarcely cordate at the base, 3.5–5.2 × 1.0– 1.8 cm. Inflorescence 1–3, arising from the apex of the secondary stems, shorter than the leaf, 2-flowered raceme each, enclosed at the base by a spathaceous, conduplicate, persistent, chartaceous bract, 4.0–7.5 × 1.5–2.0 mm when spread out; peduncle terete, 4.0–7.0 mm long, 0.30–0.35 mm in diameter, smooth, covered at the base by 1-tubular, obtuse to sub-acute, persistent, conduplicate, scarious bract, 2.4–2.8 × 0.35 mm; pedicel terete, 4.0– 12 mm long, 0.25–0.30 mm in diameter; floral bract, acute, persistent, scarious, 2.4–3.1 mm long, 0.5–0.7 mm in diameter. Ovary minutely papillose, straight to slightly arching, cylindrical, longitudinally sulcate, 1.9–2.7 mm long, 0.6–0.7 mm in diameter. Flowers small, wide-open, the dorsal sepal forming an obtuse angle with the synsepal, the sepals light amber suffused with red-purple, petals amber with red-purple spots, lip yellow-amber suffused with red-purple, column white-rose with red-purple spots, the anther cream. Sepals fleshy; dorsal sepal concave but slightly curved at the apex, lanceolate, acute, minutely apiculate, 3-veined, 6.5–7.2 × 1.7–1.8 mm; lateral sepals connate up to the apex into a fleshy, concave, ovate-lanceolate synsepal, minutely bifid at the apex, 4-veined, 6.7–7.0 × 2.5–2.6 mm, the apices obtuse. Petals fleshy, extended, ensiform, acuminate, the margins entire or minutely erose, 1-veined, 4.3–4.5 × 0.4–0.5 mm. Lip entire, fleshy, with the basal margins projecting toward the column, slightly arcuate, ovate-triangular, acute, minutely apiculate, marginally erose, articulate to the column base, glandular-papillose, covered by a translucent viscous-substance on the adaxial surface, 1.5–1.7 × 1.0– 1.2 mm; the lamina provided with a small, oblate, callus near the base. Column short, slightly arcuate, sub-terete, 0.9–1.2 mm long and 0.5–0.6 mm in diameter, with a glandular-papillose foot of 0.4–0.5 mm long; clinandrium projecting and covering the anther base, flabellate, entire at apex; stigma sub-apical, concave, covered by a viscous substance; rostellum apical, laminar, 0.3–0.4 mm long. Anther apical, obovate, glandular-papillose, 0.4 × 0.4 mm; pollinarium 0.4 mm long, formed by 2 pollinia, yellow, obovate-clavate, serous, gradually attenuated at the base, attached to a semilunate viscidium. Capsule not seen.

Distribution and ecology: —So far, Pleurothallis inaudita is only known from El Oro province in southwestern Ecuador, on the foothills of the western Andes mountain. The plant grows as an epiphyte on tree branches of Ficus Linnaeus (1753: 1059) and Miconia Ruiz & Pavón (1794: 60) above thick layer of moss, in environments of evergreen premontane forests at 883–900 m in elevation ( Figure 3 ). This species is sympatric with P. tryssa Luer (1975: 103) from subsection Acroniae , both plants are vegetatively similar in the field. The new species is present in remnant forest disturbed by human activities, where it occurs in low densities (1–3 plants per phorophyte). In culture P. inaudita flowered between April and September.

Etymology: —The specific epithet is derived from the Latin inauditus, meaning “unknown”, in reference to this rare and unnoticed plant species in the field. The type locality is situated in an area that has been extensively explored floristically, yet the species described as new had remained unnoticed by botanists.

Additional material examined (paratype): — ECUADOR. El Oro: Cantón Atahualpa, sector Cerro Azul , 900 m, 01 July 2017, Zambrano B. s.n. (QCNE!) .

Taxonomic Discussion: —The new species is member of Pleurothallis subsect. Acroniae . The sympatric P. tryssa which is vegetatively similar and belongs to P. subsect. Acroniae , can be distinguished by its multi-flowered racemose inflorescence, to 6–8 cm long (vs. 2-flowered raceme each, to 1.5 cm long), ovate-lanceolate dorsal sepal (vs. lanceolate), petals equal to or longer than the sepals (vs. nearly two-thirds the length of the sepals), a 3-lobed, acuminate lip (vs. entire, acute), with and sub-circular callus (vs. with an oblate callus) ( Figure 4 ) ( Luer 1975, 1998).

The most similar species with the new taxon is the Costa Rican P. imitor , particularly in the plant’s habit and size, leaf shape, and the overall appearance of the inflorescence and flowers. But it can be distinguished from P. inaudita by its leaves apically acute (vs. apically long acuminate), flowers yellow (vs. amber suffused with red-purple), ovate dorsal sepal (vs. lanceolate), oblong-subfalcate, acute petals, to 9 mm long (vs. ensiform, acuminate petals, to 4.3–4.5 mm), triangular-sagittate lip (vs. ovate), with an oblong callus (vs. with an oblate callus), and a longer column (2.0 mm long vs. 0.9–1.2 mm long) ( Figure 5A ) ( Luer 1998).

Some species belonging to Pleurothallis subsect. Macrophyllae-Fasciculatae, are morphologically similar to P. inaudita , but they are distinguished by their peduncles usually hidden within a spathaceous bract, shorter pedicels, petals not sigmoid, lip without basal margins projecting towards the column, and a shorter and broader column with a bilobed stigma ( Luer 1998). Within this subsection, the Ecuadorian P. crucifera Luer & Hirtz (1996b: 157) seems to be the most similar species, particularly in its floral morphology. However, it differs in its ovate, acute leaf (vs. elliptic-lanceolate, long acuminate), single-flowered inflorescence (vs. 2-flowered raceme each), ovate dorsal sepal, to 8.0– 11.5 mm long (vs. lanceolate sepal, to 6.5–7.2 mm long), narrowly triangular, acute petals (vs. ensiform, acuminate), triangular, sulcate lip (vs. ovate-triangular, non-sulcate), with an oblong callus and without basal margins projecting towards the column (vs. with an oblate callus, the basal margins projecting towards the column) ( Figure 5B ) ( Luer 2005).

Figures

FIGURE 1. Drawing of Pleurothallis inaudita Zambrano & Solano. A. Habit. B. Flower, 3/4 view. C. Flower dissection. D. Ovary and column, lateral view. E. Detail of the column with a prominent rostellum, and detail of the column, anther cap and lip, lateral view. F. Detail of the lip, frontal and ventral view. G. Anther cap and pollinarium. Drawn by B.J. Zambrano based on the holotype.

FIGURE 2. Photographic plate of Pleurothallis inaudita Zambrano & Solano. A. Habit. B. Flower, 3/4 view. C. Flower dissection. D. Ovary, column and lip, lateral view. E. Detail of the column with a prominent rostellum, and detail of the column, anther cap and lip, lateral view. F. Detail of the lip, frontal and ventral view. G. Anther cap and pollinarium. H. Detail of the 2-flowered raceme without flowers. Plate by B.J. Zambrano based on Zambrano B. 1961a and Zambrano B. s.n.

FIGURE 3. Known localities for Pleurothallis inaudita in Southwestern Ecuador. Map by B.J. Zambrano.

FIGURE 4. Specimen of P. tryssa from Cerro Azul, El Oro province, Ecuador. Photograph by B.J. Zambrano.

FIGURE 5. Drawings of similar species to Pleurothallis inaudita: A. Pleurothallis imitor, from (Luer 1998). B. Pleurothallis crucifera, from Luer (2005). Courtesy of Missouri Botanic Gardens Press.