Orchidantha anthracina H.Đ.Tr

Orchidantha anthracina H.Đ.Tr View in CoL ần, Luu & Škorničk., sp. nov. — Fig. 1 View Fig , 2 View Fig

Similar to O. vietnamica K.Larsen in general habit and colour of floral parts, but differs in dorsal sepal fully reflexed and being much narrower than lateral sepals (dorsal 9–11 mm wide, lateral 14–15 mm wide), and lateral sepals spreading and not supporting the labellum (vs dorsal sepal positioned ap- proximately perpendicular to the labellum, 12–14 mm wide,equal in width with lateral sepals, and lateral sepals overlapping and supporting the labellum in O. vietnamica ). — Type: Trần Hữu Đăng & Hiếu Cường Nguyễn TRAN-444 ( holotype SGN, including flower in spirit as part of a single specimen; iso SING, including flower in spirit as part of a single specimen), Vietnam, Phú Yên province, Đông Hòa district, Hòa Xuân Nam commune, Núi Đá Bia, N12°53ʹ18.35ʺ E109°23ʹ36.94ʺ, c. 130 m elevation, 9 Jan. 2017, flowering.

Etymology. The specific epithet is derived from the Latin anthracinus, which describes a shade of coal-black verging upon blue. It refers to the very dark velvety labellum of this species.

Small perennial rhizomatous clump-forming herb, up to 50(–65) cm tall, with 4–9(–12) leaves per shoot; juvenile plants as well as adult plants with distinctly petiolate leaves. Rhizome c. 10 mm diam, externally brown to dark brown, internally cream white; roots numerous, 5–7 mm diam, sometimes with root tubers towards the end, root tubers 2–4 by 1–1.4 cm long, fusiform, internally white with pale brown centre. Leaves to 60 cm long (inclusive petiole); petiole 5–25 cm long; lamina asymmetrical with sides unequal in width, elliptic, 23–45 by 9–14 cm, shiny on both sides, mid green to dark green adaxi- ally, slightly lighter abaxially, base oblique, obtuse to rounded, apex attenuate, margin wavy. Inflorescence on a slender, pale to cream-coloured, subterranean stem with prominent bracts and/ or their scars; prophyll triangular, 2-keeled, 10–15 mm long; second bract 2.2–2.7 mm long, cream to pale green, sometimes with a slight reddish tinge, shortly sharply cuspidate; third bract 32–40 mm long, cream to pale green, sometimes with a slight reddish tinge, shortly sharply cuspidate; floral bract appearing above the soil or with the proximal part embedded in the soil, cream white at very base, otherwise tinged purple, minutely mucronate, 52–60 mm long, sheathing the ovary extension. Flowers with a fairly unpleasant strong smell with tones of blue cheese; pedicel c. 10 mm long; ovary extension 75–80 mm long (including the c. 18 mm long ovary), cream white; sepals cream white to pale yellowish on both sides, sometimes with slight pale purple tinge externally, glabrous, unequal in size, margin entire, apex minutely cuspidate ( 1–3 mm); dorsal sepal strongly reflexed, narrowly elliptic, 70–95 by 9–11 mm (at widest point); lateral sepals narrowly elliptic, spreading (not supporting the labellum), c. 75–100 by 14–15 mm (at widest point); lateral petals overlapping at base covering stamens and style, cream white, unequally irregularly bluntly rectangular, prominently apiculate (apicule 3–6 mm long), internal margin (adjacent to the other petal) straight, exposed margins irregularly crenulate, 20–25 by 5–6 mm; labellum elliptic, 70–90 by 28–35 mm, with slightly raised midrib ( 2–2.5 mm wide at base, gradually narrowing towards the apex), very deep purple to almost black, with velvety appearance, margins entire and straight at basal 1/2–2/3, irregularly crisped, slightly undulate and with occasional incisions in apical 1/3. Stamens 8–10 mm long; filaments 2–3 mm long, swollen, cream-coloured, glabrous; anther thecae introrse, 5.5–7 mm, longitudinally dehiscent throughout the entire length, cream white to pale brown. Style cream white, 9–10 mm long; stigma 9–10 mm long, deeply 3-lobed, greenish white throughout; stigma lobes conduplicate, with whitish, semi-translucent, irregularly serrulate margin, median lobe c. 6 mm long, lateral lobes c. 3 mm long; viscidium heart-shaped, each side if the viscidium 3–3.5 mm long. Fruits and seeds not observed.

Distribution — So far known only from Phú Yên province in Southern Vietnam.

Habitat& Ecology — Lowland,evergreen,broad-leaved forest, near stream. In the field, the flowering was observed to occur from December to January, but in cultivation the plants flower 2–3 times a year.

Conservation status — As previously pointed out by Leong-Škorničková et al. (2014) Lowiaceae tend to be endemic, occurring within a very limited area, which has direct implications for conservation. The species is known only from the type locality, where it is not common. Only a single population, estimated to consist of about 300 individuals, has been found. The locality is not within any protected area and the habitat loss is a major concern for this species. We therefore propose to treat this species provisionally as Vulnerable ( VU D2 ) .

Notes — Within Vietnam and the rest of continental Asia, the morphologically most similar species is O. vietnamica , as outlined in the diagnosis. By the virtue of the same characters (strongly reflexed dorsal sepal narrower than the lateral sepals, and lateral sepals spreading, not supporting the labellum), O. anthracina can easily be distinguished from the remaining two species in Vietnam, O. stercorea and O. virosa , as well as from O. laotica K.Larsen in Laos, and O. foetida Jenjitt. & K.Larsen in Thailand, which all have the claw-shaped flower with lateral sepals at least partly overlapping and supporting the labellum. None of the five species occurring in China is similar. Orchidantha insularis T.L.Wu , O. yunannensis P.Zou, C.F.Xiao & Škorničk. and O. crassinervia P.Zou & X.A.Cai have a claw-like flower and all have a prominent median rib on the labellum, while O. chinensis T.L.Wu and O. longisepala D.Fang both have sepals dark maroon, front-facing, overlapping at base, somewhat reflexing at upper part and forming an elongated bell-like structure. In Peninsular Malaysia, all species have the dorsal sepal reflexed and the lateral sepals spreading and not supporting the labellum, but the sepals are always purple to maroon or sometimes with greenish bases or apices. Additionally, the colour of the labellum in these species is either white with basal claw (e.g., O. fimbriata Holttum , O. longiflora (Scort.) Ridl. or O. siamensis K.Larsen ), or small, broadly elliptic to almost round, and with a purplish or brown tinge ( O. maxillarioides (Ridl.) K.Schum. , O. lengguanii Škorničk. ) excluding any possibility of confusion. In Borneo, which is considered to be the centre of diversity, most species also have a claw-like flower. There are only four species with lateral sepals not supporting the labellum of which only O. inouei Nagam. & S.Sakai and O. grandiflora Mood & L.B.Pedersen might be considered somewhat similar to O. anthracina . Orchidantha inouei has a labellum with the apical quarter whitish, and sometimes also with a white central line (see colour photo in Nagamasu & Sakai 1999), therefore not confusable with O. anthracina . Orchidantha grandiflora has an entirely dark purple, almost black labellum, similar to that of O. anthracina and light to bright green sepals. The dorsal sepal reflexes, and although the lateral sepals loosely support the labellum shortly after the flower opens, they soon start reflexing and disengage from the labellum sometimes resulting in similar appearance as in O. anthracina . Although the confusion of these two species is unlikely to happen in the wild, given the vastly separate areas of distribution, they might be confused in cultivation. The main differences with O. antracina lies in the cream white to pale yellowish, unequally wide sepals, with dorsal sepal significantly narrower than lateral sepals, smaller labellum 70–90 by 28–35 mm, and shorter stamens 8–10 mm long (compared to bright green almost equal sepals, larger labellum 97–117 by 40–58 mm, and longer stamens 19–20 mm long in O. grandiflora ). Orchidantha ranchanensis Syauqina & Meekiong and O. borneensis N.E.Br. have both much smaller flowers with the labellum not exceeding 3.5 cm in length and dark purple petals (compared to labellum 7–9 cm long, and cream white petals in O. anthracina ).