Microchilus culuenensis Engels & E.C.Smidt

Engels, Mathias E. & Smidt, Eric C., 2024, Microchilus culuenensis (Orchidaceae, Goodyerinae): a new species from Southearn Brazilian Amazon, Phytotaxa 644 (1), pp. 56-62 : 57-60

Microchilus culuenensis Engels & E.C.Smidt , sp. nov. ( Figures 1–2 )

Type:— BRAZIL. Mato Grosso: Campinópolis. PCH Paranatinga II . Margem esquerda do rio Culuene [as Coluene], herbácea ca. 40 cm de altura, flores brancas, fl., 21 August 2007, A. Petini-Benelli & F.T. Tomborelli s.n. (holotype: UFMT 38455 !) .

Similar to Microchilus juruenensis ( Hoehne 1910: 30) E.C.Smidt & M.W.Chase in Smidt et al. (2021: 340), but it differs by the labellum with carina differentiated into an oblong, truncated callus at the mesochile (vs. bilamellated carina that starts from the mesochile and extends to the epichile, without differentiation into callus) and a rounded, bilobed callus at the median region of the epichile (vs. without callus).

Description:—Humicolous herb, up to 30.5 cm tall. Roots 10.0–63.0 × 1.0–3.0 mm, cylindrical, hairy, brownish. Rootbearing portion of stem ca. 3.7 × 0.2–0.4 cm, cylindrical, brown; internodes 1.4–1.5 cm long, one root per internode; foliate portion of stem ca. 21.0 × 0.15–0.4 cm, cylindrical, 6–foliate, brown; internodes 0.7–2.7 cm long. Leaves petiolate, narrow-lanceolate (elliptical in anomalous leaves); petiole + sheath 1.1–1.7 × 0.5–0.9 cm, amplective, brown; blade 4.3–6.4 × 1.1–1.8 cm, green-brownish, discolorous, base decurrent, margin entire, apex acute. Inflorescence simple, erect, racemose, ca. 11–flora; peduncle ca. 3.3 × 0.1 cm, pubescent, green; peduncle bracts 0.9–1.2 × 0.3–0.4 cm, lanceolate, base acute to rounded or amplective, margin entire and ciliate, apex acute, green to brownish, at the basal portion of peduncle amplective and at the distal portion free; rachis ca. 4.2 × 0.05–0.1 mm, pubescent, green; floral bracts 4.0–8.0 × 1.5–3.0 mm, lanceolate, base rounded, margin entire and ciliate, apex acute, green to green-brownish. Flowers with ovary + pedicel ca. 9.0–12.0 × 0.75–1.0 mm, oblongoid, pubescent, green; dorsal sepal ca. 4.0 × 2.5 mm, lanceolate, base cuneate-rounded, margin entire, apex rounded, abaxial face hairy, brown-greenish with white apex; lateral sepals ca. 4.0 × 1.75 mm, lanceolate, slightly asymmetric, base acute, margin entire, apex rounded, abaxial face hairy, brown-greenish with white apex; petals ca. 4.0 × 2.0 mm, oblanceolate and subpandurate, auriculate, asymmetric, base acute, margin entire, apex obtuse to rounded, glabrous, white with brown macules; lip 10–11.0 × 6–7 mm, subdivided; hypochile ca. 4.0 × 1.0 mm, narrow-ellipsoid, cylindrical, calcariform, apex rounded, glabrous, white; mesochile ca. 2.5–3.0 × 4.5–5.0 mm, large-ovate, margin entire, white, with an oblong and truncated central callus; lateral lobes absent; epichile ca. 3.5× 7.0–8.0 mm, anchoriform, base acute, margin entire, apex rounded to subrounded, papillose surface, white; central carina bilobed, calose and truncate in mesochile, with bilobed globose callus at center of epichile; lateral lobes subceltoid and falcate, recurved. Column ca. 4.0 × 1.5 mm; stigma ca. 0.6 × 1.1 mm, obovate, entire; rostellum ca. 2.7 × 0.4 mm, oblong, truncate and apiculate; rostellar remnant entire, with retuse scar; anther 2.3 × 1.4 mm, ovate and long apiculate, brown, acute; pollinia 2.3 × 1.0 mm, oblanceolate, two, slightly flattened, longitudinally grooved, white-yellowish. Fruits and seeds not seen.

Distribution and ecology:— Microchilus culuenensis occurs as humicolous in the forest understory, at the southern edge of the Brazilian Amazon, ecotonal region with the Cerrado domain, in the Alto Xingu river basin, state of Mato Grosso [see Docha Neto & Petini-Benelli (2006) for detailed description of vegetation]. Flowering in August. However, it is possible to expect that this species may also occur in other areas of the Xingu River basin, in the state of Pará.

Etymology:—The specific epithet refers to Culuene River, the new species was found vegetating on its banks.

Conservation status:—According to IUCN criteria (2017), M. culuenensis could be categorized as Data Deficient (DD). The new species is recorded by a single material, and more studies are necessary to locate more individuals at neighbouring areas.

Taxonomic discussion:— Microchilus culuenensis is similar to M. amazonicus ( Garay 1977: 194) E.C.Smidt & M.W.Chase in Smidt et al. (2021: 337), M. juruenensis and M. stigmatopterus ( Reichenbach 1874: 185) E.C.Smidt & M.W.Chase in Smidt et al. (2021: 344), due to the narrow leaves and labellum with anchor-shaped epichile, involute in natural position, with revolute lateral lobes.

It can be differentiated from M. amazonicus by the petals oblanceolate and subpandurate, auriculate (vs. subfalcate, slightly asymmetric, not auriculate); labellum with hypochile with entire apex (vs. bilobed), mesochile with oblong and truncated central callus (vs. bilamellate carina that starts from the mesochile and extends to the epichile, without differentiation into callus); and lateral lobes of the epichile with a rounded to subrounded apex (vs. acute and narrowly). It differs from M. juruenensis in that the labellum has a mesochile with an oblong and truncated central callus and an epichile with a bilobed callus at the median region (vs. bilamellated carina that starts from the mesochile and extends to the epichile, without differentiation into callus).

Additionally, it differs from M. stigmatopterus by its narrow-lanceolate leaves (vs. elliptical); labellum with mesochile with oblong and truncated central callus (vs. bilamellated carina without differentiation into callus); and lateral lobes of the epichile with a rounded to subrounded apex (vs. sharp and narrowly).

Figures

FIGURE 1. Holotype of Microchilus culuenenesis (A. Petini-Benelli & F.T. Tomborelli s.n.—UFMT 38455).

FIGURE 2. Microchilus culuenensis—A–B. Habit. C. Floral bract. D. Dorsal sepal. E. Petal. F. Lateral sepal. G–I. Lip. I. Detail of papillae. J–K. Column. J. Ventral view, with distended rostelum. K. Lateral view, in natural position. L. Pollinarum. Drawing by Engels from A. Petini-Benelli & F.T. Tomborelli s.n. (holotype UFMT 38455).