AMORPHOPHALLUS OPALINUS

PROTOLOGUE: Amorphophallus opalinus Serebryanyi & Hett., published in Blumea 68(1): 43 (2023).

Amorphophallus opalinus Serebryanyi & Hett., sp. nov. 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 Thuan Province, prepared from a cultivated plant originally collected in the type locality.

DISTRIBUTION: Vietnam: Vietnam.

DISTRIBUTION NOTE: Vietnam: Binh Thuan Province - Tanh Linh District, in four populations along the stream near the Dau Trau waterfall, all close together and the only ones known.².

SPECIES DESCRIPTION:

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 abaxially, as well as a prominent collective vein, 3-4 mm remote from the margin.²

INFLORESCENCE:

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, olive-brownish with irregular whitish blotches throughout, paler in the upper third. 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 rows 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 mm²; ovaries of irregular shape, depressed, bluntly angulate in cross-section, 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 or pearl-coloured, glossy, surface smooth. Male flowers consisting of 3-4 stamens; stamen 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; infructescence 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.²

ECOLOGY:

Found on a flat slope base in polydominant leafy evergreen low mountain forest of complex vertical structure, with two strata in the tree layer, under Castanopsis dongnaiensis, Lithocarpus dahuoaiensis and Anisoptera in a first stratum 20-25 m high; altitude: 450-600 m²

DISTRIBUTION MAPS:

ETYMOLOGY:

From Latin opalinus, “opaline,” for the stigmas: they are large, broadly conical and rounded like a mushroom cap, glossy, and of an opal or pearl colour found nowhere else in the genus.²

NOTES:

1. The combination of a narrow rhizome-like tuber, staminodes at the base of the male zone, a narrow spathe and large, broadly conical, almost semi-globose stigmas places Amorphophallus opalinus in a white-berried group within subgenus Metandrium. Amorphophallus linearis and Amorphophallus napiger share that combination, though the latter has yellowish berries; the stigmas of both are strikingly different from those of Amorphophallus opalinus.²

2. It shares with Amorphophallus sinuatus, a blue-berried species, an uncommon trait: the pistils are loosely set, often not touching one another, leaving bare patches of spadix axis about a square millimetre in size.²

3. Flowering in June, fruiting in November. The appendix develops a sewer-like smell at female anthesis which lasts eight to ten hours.²

4. The species is proposed as Endangered. All four known populations sit close together, and the type population grows around the top of the Dau Trau waterfall, a place many tourists visit and one likely to be altered as tourism develops.²

REFERENCES:

1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus opalinus Serebryanyi & Hett.

2. Blumea 68(1): 43 (2023) — protologue.