Corybas hamiguitanensis Tandang, Galindon & R.Bustam., 2023

Tandang, Danilo N., Docot, Rudolph Valentino A., Galindon, John Michael, Jr, Tomas Reyes, Tadiosa, Edwin R., Tandang, Sue Dixie A., Moran, Cecilia B. & Bustamante, Rene Alfred Anton, 2023, Corybas hamiguitanensis (Orchidaceae), a new species from a UNESCO world heritage site in the Philippines, Phytotaxa 598 (1), pp. 80-88 : 82-85

Corybas hamiguitanensis Tandang, Galindon & R.Bustam. sp. nov. ( Fig. 1–3 )

Type: — PHILIPPINES. Mindanao Island: Davao Oriental Province, San Isidro Municipality, La Union Barangay , Mount Hamiguitan Range Wildlife Sanctuary , 1134 m a.s.l., July 2016, Tandang 2061 (holotype PNH!, isotypes CAHUP!, CMUH!) .

Description:— Corybas hamiguitanensis resembles C. gibbifer Schlechter (1923: 21) , but is distinct by having leaves with whitish-green midrib and veins (vs. entirely dark green lamina), absence of a boss on the limb of the labellum (vs. presence), and with more nerves on the margin of the labellum (27 nerves vs. 12 nerves). A more detailed comparison of character are presented in Table 1 .

Small terrestrial herbs, 15.2–24(–37.2) mm tall from underground tuber to the flower tip, solitary or forming a small colony of 2 to less than 10 individuals, individual plants the roots are covered with mycorrhizal fungal threads. Roots terete, succulent, usually stout near the root collar, 10.3–15.2 mm long, minutely pilose becoming narrow and sparsely hairy towards the tip, 1.5–1.7 mm wide at widest part to 0.5–1.0 mm wide at the tip. Tuberoids underground, lightbrown, globose, 4.7–6.4 × 5.2–5.8 mm, villose, minutely covered with brown hairs. Stem solitary arising from the subterranean tuber, erect, white to yellowish, longitudinally channelled at the abaxial side, glabrous, 4.8–32.6 × 0.7–1.1 mm, protected at base by a persistent short, fleshy tubular sheath. Cataphyll 3.1–6.9 mm long, shortly tubular, 0.4–1.6 × 1.2–1.5 mm, with short triangular expanded upper part, 2.5–2.8 mm wide when expanded, glabrous, 1-nerved, pale green at the midrib and near apex, the apex acuminate. Leaves sessile, glabrous, young leaves dark green, cordate with white midrib and whitish veins to rarely pink; matured leaves with flower, broadly cordate, upper surface light to dark green, dull, contrasting with whitish-green veins or sometimes with inconspicuous pinkish veins, 11.4–16.3 mm long from leaf attachment to tip, to 15.2–21.4 mm from basal lobes to tip, blade 13.9–18.3 at widest point, base cordate, decurrent towards the stem, margin white, slightly to conspicuously undulate, apex acute to acuminate, acumen 0.5–1.4 mm. Veins glabrous, the midrib is straight from base to tip, impressed at the upper surface, raised below with 2 to rarely 3 pairs of primary veins on both sides, inner one usually extending into near midvein tip, middle pairs arching from half up to near tip before connecting with inner nerve, outer nerves usually very short, lateral nerves subopposite to alternate, 4 =or 7 on either side of the midrib, branching, lateral nerves on the two inner veins, 4 to 10, not branching. Floral bract, white at base to whitish green at the upper half, basal portion clasped at the ovary and becoming spreading, concave, lanceolate-triangular to narrowly linear-lanceolate when flattened 2.7–4.9 × 0.7–1.4 mm, with scattered white raphides, margin minutely crenulate, acuminate at tip. Flower 10.3–12.0 mm high (including ovary). Peduncle pale green, terete, glabrous, almost sessile, 0.6–1.4 × 0.5–1.1 mm. Ovary light brown to pink, cylindrical, 4–ribbed, 2.6–5.4 × 1–1.8 mm, slightly twisted to consistently strongly recurved making the flower facing upward position on the ground. Median sepal cucullate, exceeding and arching over the labellum, fleshy and thick, abaxial surface at basal half flecked with purple line in both side of the midvein becoming completely white at the upper part, adaxial white, purple at the upper part near apex, apex white, 16.5–21 mm long, when flattened, narrow at base, 1.5–1.9 mm wide, gradually widening at the middle, 4–5.5 mm and obovate-spathulate at the apical part, 7.2–9.1 mm, 3-veined at base, diverging into 9 or 10 at tip, margin translucent, entire to slightly minutely crenulate at the apex, apex warty at abaxial part, mucronate or apiculate with acumen 0.5–0.8 × 0.7–0.9 mm. Lateral sepals and petals, light pink, different in size, hidden behind the labellum, cuculate. Lateral sepals linear, strongly curved, 2.4–5.7 long, 0.5–0.7 mm wide at base, middle 0.2–0.4 mm wide, narrow at apical part 0.1–0.2 mm wide, margin entire, acuminate at the apex. Petals linear, shorter than the sepals, 1.3–1.8 mm long × 0.3–0.6 mm wide at base. Labellum from tubular basal part, 2.7–5.4 mm long, 3.9–4.3 mm in diameter, curving upwards and opening into a orbicular limb, 12.7–13.6 mm long, 12.5–13.1 mm wide when flattened out, reniform in shape when flattened, coarsely papillose throughout, with a distinct ovate shaped patch with echinate projections at the apical part, margin minutely toothed in distal half, becoming fimbriate towards the tip, lacerations 0.7–1.7 mm long, 0.08–0.2 mm wide, almost entirely black, with a bright magenta patch, margin white to bright magenta, 27-nerved. Paired spur white with short black line at the basal middle part on abaxial sides, conical, 1.7–3.1 × 0.8–1.7 mm. Column 2.9–3.2 mm long (including the anther cap and ventral pad). Anther cap cordate, 1.2–1.3 × 1.4–1.6 mm when flattened, central apiculum shorter than the two anther cap lobes. Stigma orbicular, 0.5 mm in height by 0.7–0.9 mm wide; ventral pad, trilobed, 1.4–1.5 × 0.9–1.4 × 1–1.7 mm.

Etymology:— The epithet “ hamiguitanensis ” refers to the type locality of this species which is Mt. Hamiguitan.

Phenology:— The species flowers during June to August.

Distribution and ecology:— In our continuous botanical survey, Corybas hamiguitanensis is found growing either solitary, or in a small group in eight sites at different elevations ranging between 626–1279 m a.s.l. within MHRWS. In small colonies, most of the plants are juvenile with one to two flowering individuals observed and collected during the visit. This species occupies various habitats from drier conditions to partly-shaded under lowland evergreen rainforest. Occasionally, their stems are buried in thick wet forest litters, growing with mosses within the forest over ultramafic rocks and or at the base of moist boulders in deep shaded environments within the mossy forest.

Proposed conservation assessment:—During the 2016 and 2019 surveys, C. hamiguitanensis was found in eight locations inhabiting different altitudinal gradients of different forest types from lowland evergreen rainforest, forest over ultramafic rocks, and mossy forest of Mount Hamiguitan Range Wildlife Sanctuary. However, a thorough population survey is needed because not enough data on its population of the species has been collected. We recommend the category of Data Deficient (DD).

Notes:— Corybas hamiguitanensis resembles C. gibbifer in having lanceolate bracts; warty, cucullate, obovate-spathulate dorsal sepal; with 3-nerves at the base and 9-nerves on the hood. The dorsal sepals of both species fall within a 15–25 mm long range. However, C. hamiguitanensis can be distinguished by its leaf with whitish-green midrib and veins (vs. entirely dark green lamina). Additionally, the peduncle of C. hamiguitanensis is longer at 0.6–1.4 mm (vs. 0.5 mm or none), having a shorter and narrower bract at 2.7–4.9 × 0.7–1.4 mm (vs. 4–10 × 2 mm), a strongly recurved ovary that is longer and narrower at 2.6–5.4 × 1–1.8 (vs. 4–7 × 3), and the shorter lateral petal 1.3–1.8 mm long (vs. 5.5–13 mm long). Furthermore, the labellum of C. hamiguitanensis differs from C. gibbifer with its orbicular (vs. suborbicular-obtuse) shape, absence (vs. presence) of the ventral inflation on the throat, absence (vs. presence) of a boss on the limb of the labellum, and the number of nerves seen on the margin of the labellum, 27-nerved (vs. 12-nerved). It can also be easily distinguished from other Corybas in the Philippines by the distinct coloration of the labellum, which is predominantly black, except for a bright magenta patch and margin on the limb.

Figures

FIGURE 1. Corybas hamiguitanensis sp. nov. A & B. Habit, individual plant growing along with mosses and ferns on substrate covered with thick forest litters, and on moist rocky substrate; C. Showing the upright position of the flower; D. Dorsal sepal, showing the abaxial side; E. Lip bordered with black shade and dorsal sepal bear dark magenta color on the adaxial apical part with short, white triangular acumen; F. Side view of the conical spur, tubular part of the labellum, and the recurved lateral sepal; G. Showing the anterior side of the ribbed ovary, abaxial surface view of lateral sepal, lateral petals, and spur; H. Flower, side view; I & J. Labellum, showing the papillose lip surface and the bright-magenta patch (Photos: DNTandang).

FIGURE 2. Corybas hamiguitanensis sp. nov. A & B. Habit, frontal and side views, showing the orbicular lip and upright position of the flower; C. Leaf; D. Floral bract; E. Expanded dorsal sepal; F. Stigma and Expanded anther cap; G. Column (Illustrated by RCampos A, D-F; DNTandang B, C, & G).

FIGURE 3. Microscopic details of Corybas C. hamiguitanensis sp. nov. A. Expanded labellum, showing the finely toothed basal half becoming incised towards the anterior margin; B. Anterior incised margin of the labellum; C. Expanded dorsal sepal; D. Dorsal sepal apex, showing the short triangular apiculum (Photos: DNTandang using Leica S8APO with MC120 HD Camera).