AMORPHOPHALLUS FUSCUS

PROTOLOGUE: Amorphophallus fuscus Hett., published in Aroideana 29: 55 (2006).

Amorphophallo asterostigmato, Amorphophallus carneo, Amorphophallus krausei, admodum forte similes, ab omnibus tribus stigmato laterali bilabiato, floribus masculinis functionalibus sed incrassatis differt.

DISTRIBUTION: N. Thailand: Thailand, Myanmar (?).

Doubtfully present in Myanmar (per POWO).

SPECIES DESCRIPTION:

Tuber depressed globose, 4–10 × 4–7 cm, dark brown, offsets rhizomatous, to 15 × 1.5 cm, scaly. Petiole 34–70 × 1–2 cm, smooth, mauve with dark brown to dark reddish brown, scattered, elongate oval or oval spots; lamina 52–80 cm in diam., rachises winged above the basal branchings; leaflets elliptic to elliptic-lanceolate, 5–20 × 2–5 cm, broadly acuminate, with short apiculum, upper side green, venation visibly highly reticulate.

INFLORESCENCE:

Inflorescence long-peduncled; peduncle 16 cm long, 7 mm in diam., smooth, brown with scattered, elliptical very dark brown spots; spathe erect, base and limb not separated, shallowly convolute in the lower part, ovate, 10 cm long, 7 cm wide, acute, outside glossy brown, the lower part with very few, scattered, small, orbicular dark brown spots, upper part darker brown towards the margin, inside pale dirty yellow-green, the base dark maroon, with several very shallow warts. Spadix sessile, as long as the spathe, 10 cm long; female zone cylindric, 12 mm long, 12 mm in diam., flowers congested; male zone subcylindric, slightly narrowing to the apex, 3 cm long, 12 mm in diam., flowers congested; appendix cylindric-conical, base attenuate, apex rounded, 5.8 cm long, 1.5 cm in diam. above the base, smooth, lower part with shallow, more or less diamond-shaped staminodes, diminishing upwards, surface off-white, developing a strong oligomethyl-oligosulphide smell.

Ovaries 4–5-angulate, apex hemispheric, 2–2.5 mm high, 2 mm in diam., base white, otherwise dirty purple, unilocular; style elongate conical, held almost parallel to the spadix, 1.5–2 mm long, 1 mm in diam. at the base, 0.8 mm diam. at the middle, apex slightly expanded and shallowly lobed, pale green, base dirty purplish; stigma very thin, 0.3 mm high, 1 mm in diam., draped over the lobes of the style apex, radially 3–4-lobed-sinuate, shallowly verrucate, dirty pale greyish. Male flowers consisting of 3–5 stamens; stamens 2.5 mm long; filaments thick, fused entirely, 2 mm long, 2 mm in diam., those of the lower flowers much broader, up to 5 mm in diam., off-white; anthers truncate, 0.5 mm long, 1 mm in diam., off-white suffused with pale dirty purple; connective broad, off-white; pores slit-like, marginal. Pollen striate.

ECOLOGY:

Found on limestone cliffs in Northern Thailand between Thailand and Myanmar

ETYMOLOGY:

From Latin fuscus, “dark,” “dusky,” or “brownish,” referring to the predominantly glossy brown to dark brown coloration of the outer surface of the spathe, particularly its darker upper portion and margins.

NOTES:

Amorphophallus fuscus shows a suite of characters that link it morphologically to such species as Amorphophallus asterostigmatus Bogn. & Hett. (Central Thailand), Amorphophallus carneus Ridl. (S. Thailand & Malaysia), Amorphophallus excentricus Hett. (S. Thailand), and Amorphophallus krausei Engl. (Burma, N. Thailand, SW China, Laos). This group has rather undifferentiated erect spathes, spadix as long as or shorter than the spathe, and elongate conical appendices. Tubers are depressed-globose or subglobose and offsets are numerous, fusiform or rhizomatous. The strong smell is similar in all. Amorphophallus fuscus differs from all these by the orientation of the style, the very thin small stigma, and the enlarged filaments in the lower male flowers. Furthermore, it has a much more dense reticulate higher-order venation in the leaflets.

The typical style and stigma of Amorphophallus fuscus is found in Amorphophallus only in Amorphophallus corrugatus N.E. Br.(Amorphophallus kachinensis Engl. is now a synonym for Amorphophallus corrugatus), from N. Thailand, Burma, and SW China. However, both of these species have near-globose appendices with strong convolutions or corrugation. The enlarged filaments of the lower flowers are found in Amorphophallus in the Amorphophallus longituberosus alliance, species of which have elongate tubers and a scent of anise. The enlarged filaments probably serve as food for the pollinators and are likely homologous to the staminodes in Amorphophallus krausei and several other species.

REFERENCES:

1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus fuscus Hett.

2. Aroideana 29: 55 (2006) — protologue.

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

Additional photos by Justin Scholten