AMORPHOPHALLUS SCABER

PROTOLOGUE: Amorphophallus scaber Serebryanyi & Hett., published in Blumea 39: 283 (1994).

Amorphophallus scaber Serebryanyi & Hett., spec. nov. Ab Amorphophallo koratensi Gagnep. in appendice spadicis partibus ceteris multo maiore, dimensionibus generatim multo maioribus differt. - Typus: Serebryanyi 8906 (MHA holo; spirit coll.), South Vietnam, Vungtau-Condao district, 10 km E of Vungtau Port, near Ngoc Thau Vien, a south-east facing slope in limestone hills, c. 150 m below the Jesus Christ Monument, in open places in thickets.

DISTRIBUTION: Vietnam: Vietnam.

DISTRIBUTION NOTE: Vietnam: the hills east of Vung Tau, the only locality known.² Also in Lam Dong, Son Dien according to Diep Dinh Quang.

SPECIES DESCRIPTION:

Tuber subglobose or depressed-globose, up to about 20 cm across and 15 cm high, weighing up to about 3.5 kg, dark brown with numerous strongly raised annular root scars, producing offsets each season, these rhizomatous, up to about 20 cm long and 2 cm across. Leaf solitary or paired; petiole up to 180 cm long and about 6 cm across at the base, the background dark brown with scattered whitish spots in juvenile plants and dark olive-green in mature ones, the base sometimes nearly black with a pinkish hue, nearly entirely covered by large rounded to elliptic confluent whitish or pinkish spots with a dark green centre, these grading to whitish green and elliptic towards the top of the petiole, the surface strongly scabrate-verrucate with elongate and often laterally fused warts. Lamina three-sect and highly decompound, up to about 180 cm across; leaflets elliptic, elliptic-oblong or lanceolate, often asymmetric, acuminate, somewhat leathery, 6-22 cm long and 3.5-9 cm broad, the base decurrent on one side, the primary and secondary veins deeply impressed, the upper surface green, the margin at first reddish violet and later whitish.²

INFLORESCENCE:

Inflorescence solitary, nearly sessile or short-peduncled; peduncle densely warted, paler than the petiole, 1-10 cm long but usually 5-10 cm, and 0.9-2.2 cm across. Spathe erect, broadly ovate, convolute for the greater part, hooded and only slightly opened at anthesis, leathery, 16-30 cm long and 15-32 cm across, the apex acute and the base strongly truncate, separated from the limb by a shallow constriction; outside dirty green or grey with a greenish tinge, bearing scattered whitish circular spots and more numerous blackish dots, the limb often with a brownish or purplish hue; inside the base very dark maroon and warted, the limb bright pale green with occasional small white spots and a brownish upper margin. Spadix subsessile, shorter than the spathe and largely hidden by it, 9-25 cm long; female zone slightly to clearly conic, 2-8 cm long and 1.8-4 cm across at the base, the flowers congested; male zone obconic or broadly fusiform, about 3.5 cm long and 1.5-3.8 cm across, the flowers congested; appendix ovoid, elongate conic or broadly fusiform-conic, obtuse, in larger specimens with a few broad longitudinal furrows, deep or shallow, creamy white, the surface smooth but with a few irregular fissures at the base separating shield-like staminodes, 3.5-13 cm long and 2-6 cm across at the base. During female anthesis it heats up considerably and gives off a smell described as strong cheese, dirty socks or decaying meat. Ovaries depressed, circular or diamond-shaped in cross section, about 3 mm across and 2 mm high, dark maroon, 2- or 3-locular; style slender, about 2.5 mm long and 1 mm across, dark maroon; stigma large, distinctly 2- or 3-lobed with rounded lobes, about 1.5 mm high and 1.2-2 mm across, bright or pale yellow, minutely echinate-scabrate. Male flowers of 3 or 4 stamens; stamens elongate, about 4 mm long; filaments short, about 0.5 mm long, connate at the base; anthers truncate, about 3.5 mm long and 1.5-2 mm across, pale salmon pink, the pores apical and elongate. Pollen released in strings, orange, psilate.²

ECOLOGY:

Found on a south-east facing slope in limestone hills at about 150 m, in open places in thickets. It flowers in May.²

ETYMOLOGY:

From Latin scaber, “rough” or “scabrous,” referring to the strongly textured vegetative surfaces of the species, particularly the petiole, which is conspicuously scabrate-verrucate. The peduncle is likewise densely verrucate, reinforcing the rough-textured appearance captured by the epithet.

NOTES:

1. Amorphophallus scaber belongs to an informal group that also contains Amorphophallus hirsutus, Amorphophallus koratensis, Amorphophallus opertus, Amorphophallus paeoniifolius and Amorphophallus prainii. The group is recognised by tubers with large annular thickened root scars, elongate offsets, large lobed stigmas, very long narrow anthers and often a rough or prickly petiole.²

2. Within that group it comes closest to Amorphophallus koratensis and Amorphophallus opertus, the three sharing a hooded spathe that opens only narrowly; every other species in the group has a bell-shaped spathe. Amorphophallus koratensis is smaller throughout and has a much smaller, massive, acute, triangular appendix deeply cracked at the base, and Amorphophallus opertus has entire stigmas and one-chambered ovaries.²

3. The leaflets are margined reddish violet when young, fading to whitish - a state not found elsewhere in the group.²

4. The tuber can weigh about 3.5 kg.²

REFERENCES:

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

2. Blumea 39: 283 (1994) — protologue.

3. Aroideana 19 (1996):P7 - 131

4. iNaturalist: Amorphophallus scaber

Additional photos by Diep Dinh Quang