AMORPHOPHALLUS OBSCURUS

PROTOLOGUE: Amorphophallus obscurus Hett. & Sizemore, published in Blumea 46: 263 (2001).

Amorphophallus obscurus Hett. & M. Sizemore, spec. nov. Amorphophallo pusillo persimilis, spathae parte dimidio inferiore angustata, stigmate fere sessili structura symmetrica. - Typus: Hetterscheid H.AM.1148-T (holo L, spirit coll.) Thailand, Ubon Ratchathani prov., Pha Taem (coll. from a cultivated plant in Leiden Bot. Garden; orig. coll. M. Sizemore).

DISTRIBUTION: E. Thailand: Thailand.

DISTRIBUTION NOTE: Thailand: Ubon Ratchathani Province - Pha Taem, the type locality and the only place it is known from.².

SPECIES DESCRIPTION:

Tuber elongate, to 3 cm long, 1 cm diam. Petiole 6 cm long, 2 mm diam., pale green; lamina 8 cm diam., consisting of only 5 leaflets; leaflets elliptic-obovate, to 5 cm long, to 3 cm diam., acuminate, upper surface green with few or numerous small, rounded, white spots.²

INFLORESCENCE:

Inflorescence solitary, short peduncled, partly subterranean; peduncle 1 cm long, 2 mm diam., smooth, white, entirely subterranean; spathe tubular, swollen in the middle, 1.7-2 cm long, 3.5-3.8 cm diam., lower part of the base convolute with margins shortly overlapping and fused along a line close to the margins, upper part of the base convolute, outside pale purplish, inside smooth, densely purple punctate, limb slightly dilated then shallowly constricted towards the narrow collar-like upper part, outside dilated part whitish, inside white, outside upper part densely brownish purple punctate or uniformly dark brown, inside similar, margin slightly undulating. Spadix sessile, longer than spathe, 7.5 cm long; female zone consisting of one whorl of flowers or only 2 or 3 isolated ones, 2 mm long, 4 mm diam., flowers distant; sterile zone 3 mm long, naked or with one or a few staminodes; male zone cylindric, 1 cm long, 2.5 mm diam., flowers distant; appendix erect, elongate, narrowly conical or nearly terete, near filiform, 6 cm long, 2 mm diam., smooth, dirty brownish, the base with or without an indistinct purplish flush. Ovaries depressed, 1 mm diam., c. 0.7 mm high, the acroscopic side slightly higher ('stylar region'), basal half white, upper half dirty purplish, white punctated, unilocular; style ('stylar region') 0.2 mm long, 0.4 mm diam.; stigma depressed, c. 0.8 mm diam., c. 0.5 mm high, shallowly bilobed, surface densely papillate, dirty brownish purple. Male flowers consisting of 1-3 stamens; stamens 1-1.3 mm long; filaments 0.3 mm long, fused, white or purplish with white punctations; anthers truncated, 0.7-1 mm long, 1-1.5 mm diam., off-white, sometimes flushed dirty purple; pores apical, slit-like; pollen unknown. Staminodes cushion-shaped or conical, depressed, c. 1 mm diam., 0.7-1 mm high, colour as ovaries.²

PROPAGATION:

Our single attempt with early September cuttings resulted in 75% rooting.

ETYMOLOGY:

From Latin obscurus, “dark” or “indistinct”: the epithet refers to the diminutive size and sand-like colouring of the spathe, which together make the plant easy to overlook.²

NOTES:

1. Diagnosis: very close to Amorphophallus pusillus, differing in the narrowed lower half of the spathe and the almost sessile stigma of symmetrical structure.²

2. Amorphophallus obscurus is obviously closely allied to Amorphophallus pusillus of Vietnam and Amorphophallus polyanthus of Thailand, sharing their diminutive proportions, colour patterns and leaf shape. It most resembles Amorphophallus pusillus, from which it differs in having almost no style, a regular depressed stigma, a thinner and longer appendix, and a more tubular spathe.²

3. The inflorescence is partly subterranean - the peduncle is entirely below ground, so the spathe opens at soil level.²

REFERENCES:

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

2. Blumea 46: 263 (2001) — protologue.

3. Alan Galloway — Amorphophallus obscurus, alangallowaybotanicals.com.

4. Propagation of Amorphophallus by Leaf Petiole Cuttings — Juniper Level Botanic Garden

Additional photos by Justin Scholten and Sira Niwesrat