Corybas circinatus Tandang & R. Bustam. 2020, spec. nov.
Creators: name: Tandang, Danilo N.
name: Bustamante, Rene Alfredanton
name: Ferreras, Ulysses
name: Hadsall, Annalee S.
name: Pym-Lyon, Stephanie
name: Robinson, Alastair S.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Asparagales
Orchidaceae
Corybas
Corybas circinatus

description: Corybas circinatus Tandang & R.Bustam. spec. nov. (Figs. 1–3)
Type:— PHILIPPINES, Palawan, Mt. Bloomfield, 331 m elevation, along trail, 10º11’50.4” N, 118º52’43.3” E, June 2012, D. N. Tandang 2060, PNH 255637 (holotype PNH!, iso- CAHUP!, KUN!).
Description:— Corybas circinatus is distinct from all known members of this genus in having a four-lobed labellum with two longer, upper lobes incurved over the two shorter lobes, a strongly cucullate dorsal sepal with a retuse apex, and a small, glandular protuberance at the front of the pedicel.
Diminutive terrestrial herb, 27–45 mm tall, growing solitarily or in clonal colonies. Raphides present in almost all plant parts. Tuber ellipsoid, 3.0–6.0 mm long × 2.0–3.5 wide, densely villous. Below-ground axes terete, 5.4–17.5 mm long, densely muricate, narrow near tuber, 0.7–1.4 mm thick, becoming broader near the root collar, 1.3–1.8 mm thick. Stem solitary, erect, terete, 3.8–21.1 mm long × 0.9–1.5 mm thick, glabrous, green with purple streak along the edges, enclosed at base by a glabrous tubular sheath (cataphyll) 4–6 mm long with a short triangular blade. Leaf solitary, borne horizontally above the ground, slightly fleshy, glabrous on both sides, broadly cordate, 14–18 mm from point of attachment to apex, up to 22 mm long including basal lobes, 14–19 mm at widest point, basal lobes sparsely overlapping, margins entire, often undulate, apex mucronate; adaxial surface minutely puncticulate, dark green with light pink to dark metallic magenta veins, sunken above and raised below, venation brochidodromous, midrib extending all the way to the apex and 4–5 lateral veins on either side of midrib, abaxial surface dark magenta. Flower solitary, nearly sessile, to 9.0– 11.5 mm high. Floral bract erect at base, incurved or spreading at apex, linear-lanceolate, 5–12 mm long × 1.0– 1.5 mm wide at base, translucent, magenta, keeled, margin crenate, apex acuminate. Pedicel enclosed by floral bract, very short, 0.4–0.6 long × 0.6–0.7 mm wide at top, with a small glandular protuberance, 0.1–0.4 mm × 0.1–0.2 mm, arising from the ventral base. Ovary erect, 3.0– 4.5 mm long × 1.2–1.5 mm wide, magenta, with ca. 5–6 longitudinal, slightly carinate ridges. Dorsal sepal strongly cucullate, concave, incurved through almost 350 degrees, nearly enclosing the entire labellum, oblong when flattened, inconspicuously 3–5 at base, becoming 9 parallel-veined at tip, 14–19 mm long, 1.4–2 mm wide at base, gradually widening to 7 –8 mm above the middle then narrowing gradually towards the blunt, downward-pointing apex, to 2–2.8 mm wide, retuse; margin otherwise entire, incurved; abaxial (outer) surface densely papillate, basal half white with occasional dark purplish ruby to carmine red streaks, apical half longitudinally banded with dark, parallel veins of a similar hue on a richly coloured purplish ruby to carmine red background. Lateral sepals and petals free, short, deep carmine, often hidden behind labellum spurs; sepals narrowly to broadly falcate, 1.0– 2.2 mm long × 0.2–0.8 mm wide; petals similar to lateral sepals, linear-lanceolate to slightly falcate, 1.2–3.5 mm × 0.2–0.7 mm wide. Labellum from an erect, tubular basal part 3.6–4.3 x 4.0– 4.8 mm in diameter with a 2.8-3.2 mm notch, becoming reflexed towards distal half, 8 mm long × 6.8 mm wide when flattened, 8-veined at base becoming 14-veined towards apex, anterior margin bilabiate with two longer, upper, lateral lobes, 5 mm × 2 mm, incurved over a shorter, lower, central, 1.5 × 4 mm lobe, the latter 3- veined, reflexed, broadly bilobed; abaxial (outer) surface glabrous and glossy, adaxial (inner) surface densely short hairy, whitish, longitudinally banded with 8 parallel dark purplish red stripes; at base with two distinct, horn-like spurs angled downwards, whitish streaked with fine purplish red lines, 1.8–2.6 mm long from ventral base of flower to tip, 1.5–2.5 mm wide at base. Column very short, 2 mm high × 1.5 mm wide, slightly curved; anther cap 0.9 mm long × 1.1 mm wide, heart-shaped when flattened, keeled, with a short mucronate apiculum produced between the lobes; stigma orbicular with swollen apical margin, 1.2 mm wide; pollinia 4, in 2 pairs, 0.5–0.7 mm × 0.1–0.2 mm, the two outer pollinia raised, the two inner pollinia lower and reduced, apparently adnate to anther cap.
Additional Representative Specimens:— Philippines, Island of Palawan, Mt. Bloomfield, 489 m elevation, along trail, 10º11′45.3″ N, 118º52′36.5″ E, flower buds, 17 June 2014, D.N. Tandang 2061 (PNH).
Etymology:— The specific epithet circinatus is the perfect passive participle of the Latin verb circinare (to make round), meaning rounded, in reference to the highly distinctive strongly incurved dorsal sepal.
Phenology:— Anthesis in Corybas circinatus has been observed on Mt. Bloomfield in May 2012 and June 2014 (D.T. pers. observ.). It was also photographed in flower on Mt. Victoria in June 2007, on Mt. Mantalingahan in July 2007, on Sultan Peak in June 2013, and on Mt. Bahile in June 2018 (all A.R., pers. observ.).
Distribution and Ecology:— Corybas circinatus is presently known exclusively from five ultramafic sites in Palawan, including: Mt. Bloomfield, Puerto Princesa, at 330–490 m elevation in shaded forest habitats in soils derived from peridotites such as harzburgite and dunite; Mt. Bahile, Puerto Princesa, at 300–450 m elevation in moderately to strongly shaded sites amongst stunted trees and scrub, particularly on moss covered clay embankments derived from degraded ultramafic rock; Mt. Mantalingahan, Rizal Province, at 724 m elevation on sheltered banks close to a watercourse near Kawayan Camp; on Mt. Victoria, Municipality of Narra, at 201 m elevation on skeletal, humic soils overlying mafic rocks bordering Nepenthes Camp on the Buhawi River; and on Sultan Peak, Municipality of Narra, at 874 m elevation in leaf litter amongst stunted, mid-montane trees close to the waterfall camp. As with most species of Corybas, this taxon appears to have rather specific habitat requirements and narrow geographic ranges that are difficult to predict even when modelled for the presence of suitable habitat. The exact suite of environmental parameters required for their survival and recruitment are still largely unknown.
Conservation Status:— The species has been documented in small numbers at five localities scattered across a 180 km range, the smallest population consisting of three plants in active growth, and the largest consisting of several colonies of 5–20 plants in the surveyed area. All observations were made on the flanks of peaks derived from the Mount Beaufort Ultramafics geological terrane, a series of outcrops of Eocene origin (Okubo 1989) that account for the majority of the mountains of Palawan, including the peaks of the Mt. Victoria Massif (Brow Shoulder, Mt. Shumkat, Sultan Peak, Sagpaw and the eponymous Mt. Victoria), which represents the largest contiguous exposed land area of this terrane (Robinson et al. 2016), as well as Mt. Mantalingahan, Escapardo Peak, Mt. Beaufort and Mt. Bahile. As such, the possibility remains for additional sites of this species being located, with the caveat that the lower reaches of this range are also currently the areas most threatened on Palawan by encroaching agricultural and subsistence practices. Such practices include the harvesting of timber for construction and for fuel, as well as the clearing of land for crop production, all of which lead to ecological shifts incompatible with the long term persistence of moisture and shade loving members of rainforest understorey herb communities.
Current observations of Corybas circinatus made in situ satisfy the IUCN 3.1 Red List EN (Endangered) Criteria B1ab(ii,iii,iv)+2ab(i,ii,iii) (IUCN, 2012), i.e. the species has an EOO <5000 km 2 and is known from 5 locations with inferred declines in area of occupancy and quality of habitat as a result of human activities causing observed degradation to two of its localities, and an AOO <500 km 2 with a projected reduction in area of occurrence, occupancy, and extent and quality of habitat.
Notes:— Corybas circinatus resembles several other Corybas species in having a strongly curved, markedly hooded dorsal sepal that encloses the labellum. Only two species with this morphology have been previously described from regions west of Wallace’s line: Corybas imperatorius and Corybas umbrosus J.Dransf. & J.B.Comber in Dransfield et al. (1986: 611), both endemic to the island of Java. While C. circinatus shares with these species dark green, broadly cordate leaves with contrasting veins, it differs in having a strongly 4-lobed labellum, a more curved dorsal sepal with a broad, retuse, incurved apex (vs. narrow, apiculate, recurved apex), and different colouration (dorsal sepal and labellum predominantly white with purplish carmine veins at the base vs. solidly purple at base). From Corybas umbrosus, the new species is further differentiated by its smaller size (10 mm vs. 20 mm tall). The new species occurs in shaded forest on ultramafic substrates at low elevations whereas both species from Java are found on other substrates at higher elevations (1070–2300 m elevation), with Corybas imperatorius found specifically in open grasslands (Comber, 1990). The new species also appears similar to Corybas smithianus Schlechter (1923: 22) (= Corysanthes triloba Smith (1910: 7) (non Hook.f.)), a poorly known species described from western New Guinea. With that species it shares both a strongly hooded dorsal sepal and a multi-lobed labellum with two lateral lobes incurved over a recurved central lobe. However, the shape of the dorsal sepal is different— C. smithianus, like the two species from Java, has an apiculate apex—and the middle lobe of the labellum is indistinctly bilobed with a crenulate-erose (vs. entire) margin. Furthermore, the protuberance/gland on the ventral pedicel of C. circinatus appears to be a unique feature within the genus, though the significance and function of this structure are currently unknown.
description: Published as part of Tandang, Danilo N., Bustamante, Rene Alfredanton, Ferreras, Ulysses, Hadsall, Annalee S., Pym-Lyon, Stephanie & Robinson, Alastair S., 2020, Corybas circinatus (Orchidaceae), a new species from Palawan, the Philippines, pp. 135-140 in Phytotaxa 446 (2) on pages 136-139, DOI: 10.11646/phytotaxa.446.2.7, http://zenodo.org/record/13877969