AMORPHOPHALLUS RAVENII

PROTOLOGUE: Amorphophallus ravenii V.D.Nguyen & Hett., published in Novon 26(1): 53 (2018).

Amorphophallus ravenii V. D. Nguyen & Hett., sp. nov. TYPE: Laos. Vientiane: Vang Vieng Distr., near Pu Kham cave, Nathoong village, 18°55'36"N, 102°23'44.8"E, 249 m, 27 May 2008, V. D. Nguyen & S. Boumanivong L-V 261 (holotype, HN!; isotype, HN!).

DISTRIBUTION: Laos: Laos.

DISTRIBUTION NOTE: Laos: Vientiane Province - Vang Vieng District, near Pu Kham cave at Nathoong village, at 249 m; known only from the type locality.².

SPECIES DESCRIPTION:

Tuberous herb; tuber irregularly subglobose with short, projecting parts at the bottom, no offset development. Leaf solitary or developing shortly after the inflorescence has disappeared; petiole cylindric, 35-45 cm, 1-1.5 cm in diam., medium to dark green, surface smooth; lamina decompound, with 3 main segments, these divided once or twice, rachises unwinged; leaflets elliptical, 5-17 x 2.5-5.5 cm, with an acumen to 2 cm, adaxial surface glossy, dark green with impressed veins, abaxial surface pale green.²

INFLORESCENCE:

Inflorescence solitary; peduncle cylindric, 35-55 cm, medium green, smooth; spathe triangular to elliptical, 15-18 x 8-15 cm, not strongly separated into base and limb, basal part at female anthesis more or less tubular, at male anthesis opening widely, outside greenish at first, turning whitish at male anthesis, inside with numerous small warts; limb erect, green outside turning white at male anthesis, inside as outside, top obtuse with a very short apiculate tip, margin curving outward at male anthesis. Spadix sessile, equal to or slightly shorter than spathe; female part cylindrical, 1-2 cm, 1-1.8 cm diam., pistils densely congested; male part cylindrical or slightly fusiform-conical, 6-8 cm, 1.2-1.8 cm diam. at the base, 1-1.5 cm diam. at the apex; appendix short-conical, about half as long as the male part, 3-4 x 2.2 cm at the base, base sometimes constricted and slightly broader than the top of the male portion, apex obtuse, surface slightly rugulose, white. Ovaries strongly depressed, 2-2.2 mm diam., green, unilocular with 1 basal ovule; style conical, stout, ca. 1-1.5 mm, green; stigma discoid, wider than the ovary, 2.1-2.3 mm wide, entire with a central depression from which a few shallow, short grooves radiate, or shallowly 3- to 6-lobed. Male flowers consisting of 4 to 6 stamens in the basal part of the male zone, 2 to 4 stamens in the upper part; filaments wedge-shaped, 0.5 x 1.2 mm; anthers oblong, truncated, 0.6 x 1.2 x 0.7 mm, opening by apical slit-like pores. Fruiting part of infructescence short-cylindrical, berries congested; berries 13 mm long, 10 mm diam., glossy, dark blue, 1-seeded; seeds ovate, 11 mm long, 8 mm diam.²

ECOLOGY:

Found in humus-rich soil in evergreen, seasonally wet forest on a limestone mountain; altitude: 249 m²

ETYMOLOGY:

Named in honor of Peter Raven of the Missouri Botanical Garden.²

NOTES:

1. Diagnosis: Amorphophallus ravenii closely resembles Amorphophallus khammouanensis and Amorphophallus croatii, but differs in an appendix about half the length of the male zone rather than as long or longer, stigmas about 1.5 times as broad, unwinged rachises on the decompound leaf blade rather than winged, and a subglobose rather than depressed globose tuber.²

2. A good many species share this general spadix and spathe pattern - a very simple green spathe with no strong separation of base and limb, and a spadix of about the same length carrying nothing but a male zone, a female zone and an elongate conical obtuse appendix. The blue berries narrow the comparison to a blue-berried group within subgenus Metandrium.²

3. The two most similar species, Amorphophallus khammouanensis and Amorphophallus croatii, both come from Khammouane Province in Laos. Beyond the characters in the diagnosis, both have bilocular ovaries where Amorphophallus ravenii has unilocular ones.²

4. The species is proposed as Critically Endangered. It is known from a single subpopulation with an area of occupancy estimated at 4 km², in a place where forest degradation is advancing with increasing tourism.²

REFERENCES:

1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus ravenii V.D.Nguyen & Hett.

2. Novon 26(1): 53 (2018) — protologue.

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