AMORPHOPHALLUS LEPTOSOMA

PROTOLOGUE: Amorphophallus leptosoma Hett., J.Borgmann & Prehsler, published in Aroideana 47(1): 6 (2024).

Amorphophallus leptosoma Hett., J.Borgmann & Prehsler, sp. nov. Diagnosis: Amorphophallus leptosoma shows the strongest morphological similarity to Amorphophallus sakonnakhonensis and Amorphophallus harmandii Engl. & Gehrm. Essential differences between Amorphophallus leptosoma and Amorphophallus harmandii are the latter's distinctly more complex leaf blade, the smooth style (vs ridged in the latter), the entire ovary (vs lobed in the latter) and the entire stigma margin (vs sinuously lobed in the latter). The essential differences of Amorphophallus leptosoma with Amorphophallus sakonnakhonensis are the more slender appendix of the first and the staminate part and pistillate part being adjacent in the first vs a sterile zone between staminate and pistillate parts, clothed with synandrodes in the latter. Type: Cultivated in the former Wageningen University Botanical Gardens, Hetterscheid H.AM.1720-T, 12 June 2008, [orig. coll. Thailand, Lopburi Prov. (without precise locality), Alan Galloway AGA-1736-01, 21 September 2001] (holotype BR, spirit collection).

DISTRIBUTION: Thailand: Thailand.

DISTRIBUTION NOTE: Thailand: western Thailand, Kanchanaburi Province, in Erawan National Park; and central Thailand, Lop Buri Province, the source of the original collection, which carries no precise locality.².

SPECIES DESCRIPTION:

Tuber narrowly elongate, 10-40 cm long and 0.8-1.5 cm in diameter, unbranched. Leaf solitary; petiole very slender, 10-40 cm long and 0.3-0.7 cm in diameter, smooth, largely uniformly pale green, the lower third with a pale greyish hue and scattered small elongate, narrowly linear or narrowly elliptic white spots, and in some plants several tiny dark green dots as well. Lamina 10-36 cm in diameter, carrying very few larger leaflets - three to seven - together with one or two very small subsidiary ones; leaflets elliptic to elliptic-oval, 1.8-7 cm long and 1.8-7.5 cm broad, the upper surface uniformly mid green, the lower surface uniformly pale green, the tip shortly acute-acuminate.²

INFLORESCENCE:

Inflorescence solitary; peduncle 10-20 cm long and 0.3-0.5 cm in diameter. Spathe erect, concave, not constricted, broadly ovate when spread out, 4.5-7.5 cm long and 4-6.5 cm broad, the tip acute; outside uniformly mid green, turning whitish green during male anthesis; inside whitish green, the base slightly darker and set with scattered small, slightly irregular warts. Spadix sessile, longer than the spathe, 10-16 cm long. Pistillate zone cylindric, 0.6-1.2 cm long and 0.4-0.9 cm in diameter, the pistils congested. Staminate zone elongate conical, slightly narrowed at the base, 3-4.8 cm long and 0.6-1.2 cm in diameter at the base, tapering to 0.4-0.8 cm at the top; the stamens slightly distant near the base and congested through the rest of the zone. Appendix narrowly elongate conical, the base slightly narrowed or not, 9 to about 14 cm long, tapering to the tip, the surface shallowly rugulose with scattered shallow longitudinal furrows, pale green at first and turning off-white at male anthesis, the apex subacute. Ovaries depressed globose, prismatic, 1 mm high and 2 mm in diameter, pale green, one-chambered; style 0.8-1 mm long and 0.5 mm in diameter, set perpendicular to the spadix axis or pointing slightly upwards, pale green; stigma depressed and thin, entire or very shallowly two-lobed and two-lipped, about 0.2 mm high and 0.9-1 mm in diameter, the surface smooth with a very shallow central depression, dirty whitish. Male flowers mostly of one to three stamens, but in the lower part of the staminate zone in larger plants rising to five or six, and occasionally more where neighbouring flowers fuse into irregular synandria; anthers sessile, largely free and joined only over a very short stretch at the base, off-white, 1.5-3 mm in diameter and 1 mm high, rectangular or irregularly prismatic seen from above; filaments absent; thecae flattened at the top, the pores slightly bean-shaped, becoming oval after anthesis. The infructescence has never been seen.²

ETYMOLOGY:

The epithet refers to the very slender build of every major part of the plant.²

NOTES:

1. The species was in cultivation for more than twenty years before anyone named it. Alan Galloway collected the original tubers in Lop Buri Province in September 2001; they were grown at the Wageningen University Botanical Gardens as H.AM.1720, and when that garden closed the plant moved to the Hamburg Botanical Garden as HBG 2014-G-205. It was recognised as new only after the second author flowered tubers of unknown Thai origin and sent photographs to the first. The type is the Wageningen plant, preserved in spirit in 2008.²

2. Its close resemblance to Amorphophallus harmandii places it in Amorphophallus subgenus Metandrium.²

3. It is told from Amorphophallus harmandii by the leaf and by three details of the flower: Amorphophallus harmandii has a distinctly more complex leaf blade, a ridged style, a lobed ovary and a sinuously lobed stigma margin, where this species has a smooth style, an entire ovary and an entire stigma margin.²

4. It is told from Amorphophallus sakonnakhonensis, the species it most resembles, by a more slender appendix and by the male and female zones of the spadix meeting directly - Amorphophallus sakonnakhonensis carries a sterile zone between them, clothed with synandrodes.²

5. ⚠ The same paper corrects the description of Amorphophallus sakonnakhonensis. Those synandrodes are visible in that species' own published photograph and line drawing, but its 2023 protologue never mentions them. Having checked plants from several sources, the authors conclude the character is consistent and publish it as a formal emendation: the synandrodes are few, gibbous, rhombic or angulate, with a slightly raised connective remnant, and at male anthesis they turn into echinate bristles, the whole zone drying out.²

REFERENCES:

1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus leptosoma Hett., J.Borgmann & Prehsler

2. Aroideana 47(1): 6 (2024) — protologue.