AMORPHOPHALLUS SUMAWONGII

PROTOLOGUE: Amorphophallus sumawongii (Bogner) Bogner & Mayo, published in Aroideana 8: 19 (1985).

Amorphophallus sumawongii (Bogner) Bogner & Mayo, comb. nov., Aroideana 8(1): 19 (1985). Type: Thailand, Wathana Nakhon, near Ban Boa Nang Ching, 14 Mar. 1971, J. Bogner 372 (M holotype; K, M, US isotypes). Thomsonia sumawongii Bogner in Plant. Syst. Evol. 125: 15 (1976), synon. nov.

SYNONYMS:

HOMOTYPIC SYNONYMS: Thomsonia sumawongii Bogner in Pl. Syst. Evol. 125: 15 (1976)

DISTRIBUTION: SE. Thailand: Thailand.

DISTRIBUTION NOTE: Thailand: the south-east, at Wathana Nakhon in Sa Kaeo province. It is endemic to Thailand.⁵.

SPECIES DESCRIPTION:

Tuber turnip-shaped and irregularly branched, 6-20 by 2-6 cm. Leaf solitary; petiole smooth, 20-40 cm by 6-10 mm, greenish or reddish, marked to a varying extent with narrowly elongate whitish, greenish grey or reddish grey spots. Leaf blade 20-80 cm across, the rachises narrowly winged in the distal half; leaflets elliptic to oblong-elliptic, 7-21 by 3.5-8 cm, acuminate, dark green above and brighter beneath.⁵

INFLORESCENCE:

Inflorescence solitary and long-peduncled; peduncle as the petiole, 27-60 cm by 4-8 mm. Spathe erect and elliptic, the base shortly convolute and the apex acute and more or less hooded, 6-8.5 by about 3 cm, yellowish, bright green, or more or less purplish or reddish with yellowish spots, the base within minutely warted and bearing some scattered larger spines. Spadix shorter than the spathe, sessile, 4-8 cm long; female zone cylindrical, 5-10 by about 5 mm, the flowers congested; ovaries subglobose or obovate, slightly depressed, more or less diamond-shaped in cross section, 1.7-2 mm, bright green; stigma sessile and small, disc-shaped, circular in cross section, about 0.5 mm across and 0.1-0.2 mm high, yellow, the surface warted and often with a few shallow depressions. Male zone cylindrical, 1.5-2.5 cm by 6-9 mm, the flowers lax and the lower ones further apart than the upper; male flowers of 2-3 stamens, the lower ones larger; stamens 2-3 mm long, yellow. Appendix conical with an obtuse or subacute apex, 1.8-4.5 by about 1 cm, white, and entirely covered with staminodes; these elongate and truncate, free or partly to entirely joined, about 1.5-2.5 by 0.5-2.5 mm, rounded or irregular in cross section. Infructescence cylindrical, about 4 by 2 cm; fruits globose, about 5 by 5 mm, the surface wrinkled and ribbed in places, pale green when ripe.⁵

ECOLOGY:

Found in dry dipterocarp forest at about 120 m.⁵

PROPAGATION:

Our best luck with this species was with mid-July cuttings which rooted at 51.3%. By early September, our best rooting was at 28.6%.

ETYMOLOGY:

Named for Sumawong, in whose honour Bogner published the plant in 1976 as Thomsonia sumawongii; Bogner and Mayo moved it into Amorphophallus in 1985.²

NOTES:

1. The appendix is covered from base to tip with staminodes - elongate, truncate bodies up to 2.5 mm long, free or fused to one another. It is that character which made the species matter out of proportion to its size.²

2. Thomsonia had been separated from Amorphophallus on the structure of the appendix: densely tuberculate in Thomsonia, with projections read as modified male flowers, and smooth in Amorphophallus. In this species the structures are more distinct and more clearly staminodes than in Thomsonia napalensis itself - and Engler had already conceded in his own key that the appendix in Amorphophallus may be warted or wrinkled as well as smooth. The character could not carry the genus, and Thomsonia was sunk.²

3. Until this species was described, Thomsonia rested essentially on the single species Thomsonia napalensis. The only other one recognised, Thomsonia hookeri, was known from one mixed sheet at Kew and had never contributed to the definition of the genus.²

4. The inflorescence resembles that of Amorphophallus longituberosus but differs markedly in the elongate staminodes on the appendix. It also recalls the Pseudodracontium group within Amorphophallus, but differs in two-chambered anthers and in always flowering before the leaf.⁵

5. The inflorescences are sold in markets and eaten as a vegetable after boiling, and are said to taste of asparagus. The plant is known as buk in the south-east of Thailand.⁵

6. The fruits are unusual for the genus: dryish, pale green at full ripeness, and wrinkled and ribbed rather than a smooth bright berry.⁵

7. The authors of the combination went further than the Flora of Thailand does: they note that the species closely approaches Pseudodracontium in its well-developed staminodes and long stamen filaments, and could be regarded as intermediate between the two. Pseudodracontium has since been sunk into Amorphophallus altogether.²

REFERENCES:

1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus sumawongii (Bogner) Bogner & Mayo

2. Aroideana 8: 19 (1985) — protologue.

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

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

5. Araceae, in Flora of Thailand 11(2): 101-325 (2012)