Amorphophallus opalinus Serebryanyi & Hett., 2023

Amorphophallus opalinus Serebryanyi & Hett. View in CoL , sp. nov. — Fig. 4 View Fig , 5 View Fig , 6 View Fig

Etymology. The epithet ‘ opalinus ’ alludes to the colour of the unique stigmas of the species.

Amorphophallus opalinus is diagnosed by a narrow rhizome-like tuber with enlarged basal part, staminodes at the base of the male zone of the spadix, a narrow spathe, large, broadly-conical with rounded apex, opalescent stigmas and white, one-seed berries. — Type: Tan Trinh s.n. (holo MHA), South Vietnam, Tanh Linh District , Binh Thu ận Province, prepared from a cultivated plant originally collected in the type locality .

Seasonally dormant tuberous herb flowering before the leaf. Tuber narrowly elongate, vertically growing, flexible, usually deformed as a result of growing around barriers or through very narrow holes, up to 9(–10) cm long, 2–2.5 cm diam at the top, less than 1 cm diam in the narrowest part, light yellow-brownish when mature, whitish when juvenile, basal part occasionally enlarged. Cataphylls narrowly triangular in outline, acute at the apex, up to 5 cm long, drying pale brown, remaining intact. Leaves 1–2 per tuber (when 2, one leaf always bigger); petiole 35–40 cm long, 5–7 mm diam, smooth, green (or olive-green) with irregular brown (or khaki-brown) blotches up to above the middle (sometimes the upper blotches dark green) and numerous tiny whitish and blackish green stripes and spots throughout; lamina up to 35(–40) cm diam, each of the 3 principal segments consists of 5 (rarely 7) leaflets arranged as 2 (or 3) pairs of lateral and one terminal; lateral leaflets often not opposite, especially the basal ones; rhachises narrowly canaliculate, only winged (sometimes broadly so) in their distal parts; leaflets linear- to elliptic-lanceolate (rarely ovate), c. 9 by 2(–2.5) cm long, thin-coriaceous, base more or less broadly cuneate, sometimes shortly decurrent, apex long acuminate, margins undulate, upper surface dull green to green, matte, lower surface paler; primary lateral veins (c. 10 pairs) together with the midrib significantly impressed adaxially, raised abaxi- ally, as well as a prominent collective vein, 3–4 mm remote from the margin. Inflorescence solitary, long-pedunculate; cataphyll similar to those appearing with the petiole but longer, up to 7 cm long; peduncle up to 30 cm long, 5 –7 mm diam, smooth, olivebrownish with irregular whitish blotches throughout, paler in the upper 1/3. Spathe ovate-oblong, 7– 9 by c. 6 cm diam, erect, apex obtuse to rounded (sometimes shortly apiculate), only the basal 1.5 cm convolute, lower spathe/base and limb not differentiated, outside uniformly pale green with slightly darker veins, inside as outside, but with numerous tiny whitish green warts arranged longitudinally in the central part and with a metal-greyish area at the base, 2 – 3 cm long; margin whitish. Spadix sessile, up to 2.5 times longer than the spathe, 21– 22 cm long; female zone cylindric, c. 2 by 0.8 cm diam, pistils not congested; male zone elongated, cylindric to slightly obconic, 4.5– 5 by 7– 8 mm diam at the base, about 1 cm diam at the top, flowers congested, the lowest row(s) consisting of sterile staminodes somewhat bigger than regular male flowers, decaying when the pollen is released; appendix elongate, to 15 cm long, c. 1.1 cm diam at the base, the thickest part c. 1.4 cm at c. 4 cm from the base, from there tapering to the obtuse or slightly rounded apex, base not constricted, surface with irregular shallow grooves and depressions, ivory-white to creamy pale yellow, developing sewer-like smell at female anthesis, lasting 8 –10 hours. Pistils c. 30 per spadix, often not adjacent to each other, leaving open axis areas c. 1 mm 2; ovaries of irregular shape, depressed, bluntly angulate in crosssection, c. 1 by 2 mm diam, dark green, unilocular, one basal ovule. Style prominent, 0.7– 0.8 by 0.6 – 0.7 mm diam, white; stigma large, broadly conical, rounded at the top (mushroom cap-shaped), c. 1.5 mm diam, opaline/pearl-coloured, glossy, surface smooth. Male flowers consisting of 3 – 4 stamens; sta- men 3 –3.5 mm long, filaments 2– 2.5 mm long, base connate; anthers c. 1 by 1.2– 1.5 mm diam, truncate, pores apical. Pollen released in strings, coarsely striate, yellow. Fruiting peduncle same size as the flowering one but somewhat thicker; infructes- cence 5 by 2 cm diam. Berries slightly depressed-globose or globose, c. 7 mm diam, milky-white when ripe (green while maturing), crested by the old stigma remnant (a brownish dot), one-seeded.

Distribution — Amorphophallus opalinus is only known so far from the close vicinity of the type location ( Fig. 1b View Fig ). Four populations of A. opalinus (including that from which the type was derived) were found near each other along the stream near the Dau Trau waterfall.

Habitat & Ecology — All the studied populations were found on a flat slope basis in polydominant leafy evergreen low mountain forest of complex vertical structure (2 strata within the tree-layer). Altitude 450– 600 m. Castanopsis dongnaiensis Son & Ngoc , Lithocarpus dahuoaiensis Ngoc & L.V. Dung (both Fagaceae ), Anisoptera sp. ( Dipterocarpaceae ) predominant in the 1st tree-stratum (20–25 m high).

Phenology — Flowering: June; fruiting: November.

Provisional conservation status — Amorphophallus opalinus is known from four closely situated localities only, with a type population of several individuals around the top of the Dau Trau waterfall which is visited by many tourists. This place will possibly change due to the development of tourism in the future, which will negatively affect the habitat of the species. We herein propose this species to be treated as ‘Endangered’ (EN B2 ab(iii)) following the Red List criteria of the IUCN (2019).

Notes — Amorphophallus opalinus demonstrates a combination of characters suggesting it belongs to a white-berried clade of subg. Metandrium Stapf ( Claudel et al. 2017): narrow rhizome-like tuber, staminodes at the base of male zone of the spadix, narrow spathe, large, broadly-conical with rounded apex (almost semi-globose) stigmas. Amorphophallus linearis Gagnep. and A. napiger Gagnep. share that combination of characters, although the latter has yellowish berries. However, the stigmas of those species are strikingly different in comparison to those of A. opalinus ( Fig. 7 View Fig ).

Amorphophallus sinuatus Hett. & V.D.Nguyen (having blue berries) shares a relatively rare pattern with A. opalinus , the peculiar loose arrangement of pistils, often not adjacent to each other, leaving open axis areas about 1 mm 2. However, the unique pistil of A. opalinus with its glossy opaline stigma with large, broadly conical, rounded top and smooth surface, on a prominent thick style (up to 0.8 mm long) differs from the pistil of A. sinuatus , the latter being depressed, shallowly three-lobed and sitting on a short style 0.2–0.4 mm long.