Corybas kaiganganianus Tandang, A.S.Rob.

Delos Angeles, Marjorie D., Buot Jr, Inocencio E., Moran, Cecilia B., Robinson, Alastair S. & Tandang, Danilo N., 2022, Corybas kaiganganianus (Orchidaceae), a new, rare helmet orchid from Samar Island, Philippines, Phytotaxa 543 (2), pp. 127-134 : 128-131

Corybas kaiganganianus Tandang, A.S.Rob. & M.D. Angeles, spec. nov. ( Figs 2–3 )

Type:— PHILIPPINES. Samar Island: Paranas , Samar Island Natural Park , 360–380 masl, 11°48’35“N, 125°9’55“ E, 26 Oct 2021, Angeles 338 (Holotype: PNH!; Isotypes: USTH!) .

Corybas kaiganganianus is similar to the Malay Peninsula species, C. ridleyanus Schlechter (1923: 20) with reference to leaf shape, overall leaf dimensions, ovary dimensions and long lateral petals and sepals. It is distinguished by the absence of a boss, fleshy, strigose hairs at the centre of the lip and a narrow ventral pad.

Terrestrial herbs, 29.2–31.1(–38.5) mm tall with an underground tuber, growing solitarily or in small clonal colonies of 3–5 individuals. Tuber globose or ovoid, 5.3–6.6 × 4.6–5.7 mm, villous, brown. Stem erect, terete, glabrous, pale green, 5.3–6.6 × 1.6–1.8 mm, surrounded at the base by a cataphyll with no or inconspicuoustube, ovate when expanded, 4.8–6.7 × 3.5–4.7 mm, opaque and light green turning darker towards the tip, margin minutely undulate, apex acuminate, acumen 1.4–1.6 mm, glabrous. Leaf single, held horizontally above the ground, glabrous on both surfaces, broadly cordate in outline, 9.5–15.0 mm from petiole attachment to apex, up to 17.9 mm long including basal lobes, 8.1–14.1 mm at broadest part, the basal lobes overlapping when young and becoming cordate when mature, margin entire, complanate to slightly undulate, decurrent into the stem, glabrous apex acuminate, adaxial surface green contrasting with white midrib and veins, green to pale violet abaxially and minutely papillate. Veins glabrous, midrib and veins flat above and usually raised below, the midrib on lower surface pale green, slightly broader at base, becoming narrow all the way to the apex, with 3 pairs of parallel veins on each side, only the two inner pairs conjoining near the tip of the midrib, two middle pairs curving to almost ¾ before coalescing into the inner pair, outer pair similar in length to the basal lobes, lateral nerves 4–6 on each side of the midvein, opposite to alternate, branching into two, while the lateral veins on the either sides of the inner veins number 6–10,unbranched. Floral bract erect, adnate to the dorsal sepal, linear-lanceolate, 8.5–11.3 × 1.4–1.9 mm at base and 0.3–0.5 mm at apex, cucullate, keeled, margin entire, apex acuminate and rarely reflexed, light green at the base turning pale towards the tip. Peduncle yellow green, glabrous, terete, very short 0.16–0.18 × 0.45–0.52 mm. Ovary yellow-green, cylindrical, twisted, erect 4.9–5.72 × 1.3– 1.4 mm, glabrous, 4-ridged. Flower terminal, solitary 9.2–9.6(–11.1) mm high. Dorsal sepal erect below, progressively becoming curved at the middle and reflexed towards the apex, cucullate, tightly clasping the involute margin of the labellum, 12.2–17.5 mm long, base narrow, 2.3–3.4 mm wide, gradually widening to 5.8–8.4 mm and, then abruptly expanding to form cordate shaped hood, 6.61–10.12 mm, two apex side lobes, obtuse, 4.0– 4.4 mm wide, 3–4 veins at the base and branching to 13–15 towards margin of apex, semi-translucent, white at the base becoming dark burgundy at the apex, glabrous. Lateral sepals and petals are similar in shape, linear-filiform, longitudinally concave, white below, later becoming pale magenta above. Lateral sepals projecting behind spurs, longer than the petals, 33.9–59.7 mm × 0.6–0.9 mm wide at base, middle 0.90– 0.50 mm, near apex 0.12–0.30 mm, gradually curving upward towards the tip. Lateral petals spreading horizontally, emergent in between the conical spurs, 24.9–37.1 mm × 0.5–0.8 mm wide at base, middle 0.4–0.7 mm, near apex 0.2–0.5 mm. Labellum margin involute from base to apex and forming a tube, 11.6–11.8 × 8.4–8.9 mm, narrow, basally erect then curving strongly downwards in distal half by ca. 240–250º, the broad apical part of both dorsal sepal and labellum clasping tightly together and forming a circular tube opening, 2.5–3.3 long × 5.5–6.9 mm wide; centre of lip blade light pink, with numerous minute, strigose hairs banded with white to broad burgundy along their margins; the expanded labellum broadly ovate, 11.6–11.78 × 8.44–8.85 mm, adaxial (inner) surface white with a broad, burgundy band along the margin, abaxial surface whitish pink with light pink veins; paired spurs covered behind by the labellum and diverging sideways, conical, 0.9–1.3 × 0.6–0.9 mm, white. Column 1.33–1.42 mm long, held upright. Anther cap cordate when expanded, 0.73–0.80 × 1.05–1.10 mm, with short triangular apiculum. Stigma orbicular, 0.55–0.71 × 0.70–0.83 mm. Ventral pad 0.43–0.78 × 0.31–0.55 mm. Pollinia 4, mealy, in 2 pairs, each 0.039 –0.056 × 0.019 –0.023 mm, adnate to anther cap. Capsule not seen.

Distribution and ecology:— Observed to thrive in mosses and humus at summit of a forest on limestone, 360– 380 m. No floral visitors observed during the visit to the site.

Etymology:— The specific epithet “ kaiganganianus ” is derived from the local term “kaigangan” used by the locals to refer to the forests over limestone where the new species was collected.

Phenology:— Flowering October.

Conservation status:— The new species faces erosion from surface runoff, poaching, the limited extent of its threatened habitat type and climate change. Corybas kaiganganianus has only been recorded on moss covered peaks and cliffs within Samar Island Natural Park. The extent of occurrence is ≤ 10 km 2, with a population of c. 25 mature individuals observed over the course of a series of botanical surveys conducted in April 2016, July 2019, June 2021, September 2021 and October 2021 (~49 days). Owing to its small population and area and extent of occupation, C. kaiganganianus qualifies as CR (critically endangered) under the IUCN 3.1 Red list criteria B2ab(i, ii,v) ( IUCN, 2012).

Notes:— Corybas kaiganganianus was compared to C. ridleyanus because of their shared villous tuber, cordate leaf shape and long lateral petals and sepals. Furthermore, the range of dorsal sepal width is similar to that of C. ridleyanus (2.3–10.12 vs 6 mm). However, the species differ in the size of the tuber (5.3–6.6 × 4.6–5.7 vs 35.0 × 3.0 mm) and column length (1.33–1.42 vs 2.5 mm). Corybas kaiganganianus was further compared with C. comptus Dransfied & Smith (1983: 606) due to similarities in their labellum width (8.4–8.9 vs 8 mm). Also, both species share the same colour patterns at the labellum (white with a burgundy/deep crimson band along the margin) but C. kaiganganianus may be distinguished from C. comptus based on the spur colour (white vs deep crimson) and the number of veins at its widest point near the apex (13–15 vs 7). In addition, C. kaiganganianus is distinct from C. ridleyanus and C. comptus ( Table 1 ).

Figures

FIGURE 2. Corybas kaiganganianus. A. Habitat. B–C. Plant in natural habitat. D. Base of the labellum showing the four-ridged ovary, conical spurs, lateral sepals emerging between the conical spur and the lateral petals. E. Lateral view of sterile plant. F. Cataphyll. G. Front view at anthesis. H. Lateral view at anthesis. I. Back view at anthesis. J. Top view at anthesis. K. Back view of labellum. L. View of the hairs at the labellum. M. Labellum flattened abaxial view. N. Labellum flattened adaxial view. (Photography by MD delos Angeles.)

FIGURE 3. Corybas kaiganganianus. A. Habit. B. Flower lateral view. C. Dorsal sepal, flattened. D. Cataphyll, flattened. E. Floral bract, flattened. F. Column, showing pollinarium and stigma. G. Column lateral view, showing anther cap. H. Leaf. (Illustration by Danilo N. Tandang).