Amorphophallus infundibuliformis: The Unique Peat Soil Aroid of Borneo
Hidden within the sandy peat forests of West Kalimantan and Sarawak grows one of the most morphologically distinctive members of its genus. Amorphophallus infundibuliformis Hett., A. Dearden & A. Vogel holds a singular distinction: it is the only species in the entire genus known to carry uncinate (hook-shaped) staminodes on the lower portion of its appendix. Hetterscheid, Dearden, and Vogel formally described it in 1994 in the journal Blumea. Its small, funnel-shaped inflorescence belies the complexity of its floral architecture. For aroid enthusiasts and plant ecologists, this species represents a fascinating example of extreme morphological specialization in a highly specific and fragile ecosystem.
Taxonomic Identity of Amorphophallus infundibuliformis
Amorphophallus infundibuliformis belongs to the family Araceae. Hetterscheid, Dearden & Vogel described it in Blumea 39 (1994): 259. No synonyms are currently recognized for this species.
Morphological Description
Tuber and Leaf
The tuber of Amorphophallus infundibuliformis is depressed-globose to subglobose and pinkish in color. It produces no offset structures. The plant bears a single solitary leaf. The petiole surface is dirty whitish and carries numerous confluent, irregular green spots along with scattered, more or less raised white dots. The petiole top develops into an intercalary bulbil. Leaflets are elongate-elliptic and long-acuminate, with numerous small undulations on the margin. Their main veins are impressed. The upper surface is green and moderately glossy.
Inflorescence and Peduncle
The inflorescence of Amorphophallus infundibuliformis is short-peduncled. The peduncle measures approximately 4 cm long and about 0.8 cm in diameter at the base. It is hidden within the cataphylls. In fruit, the peduncle lengthens considerably.
Spathe
The spathe is funnel-shaped (infundibuliform) and strongly convolute in its lower half. In side view it is obconic, and in front view it is transversely orbicular-elliptic. It measures approximately 6 cm long and about 8 cm in diameter, and terminates in a very widely acute apex. Internally, the lower half of the base is dark maroon. The inner base surface carries strong, longitudinal ridges.
Spadix and Floral Zones
The spadix of Amorphophallus infundibuliformis is sessile and obliquely inserted, slightly longer than the spathe. The female zone is oblique and very short-cylindric, 0.5–1 cm long and approximately 1 cm in diameter. Flowers in the female zone are congested. The male zone is cylindric with an oblique base, 0.8–1.3 cm long and approximately 1 cm in diameter. Flowers in the male zone are congested and partly ridge-like in arrangement.
The appendix is cylindric and obtuse. It reaches up to 6.5 cm long and approximately 1 cm in diameter. The appendix is entirely and densely covered by staminodes. In the lower third of the appendix, these staminodes are shortly conical to aristate, and sometimes uncinate (hooked). Some carry long, narrowly decurrent, ridge-like bases. Moving upward, the staminodes become shorter or reduce to only their basal portion, reaching up to 2 mm in length. The color of the appendix is whitish overall.
Female Flowers
Each ovary is depressed, irregular to cubic, and angulate in cross-section. It measures 0.9–1.5 mm in diameter and 1.2–1.5 mm tall. The color is reddish-brown, becoming maroonish near the style insertion. Each ovary is unilocular. The style is either absent or only basiscopically developed. The stigma is sessile or partly sessile and acroscopically orientated. It is reniform in shape, with a shallow central depression and one conic lobe on the outward-facing margin. It measures 0.8–1 mm in diameter and 0.3–0.5 mm tall. Its color is dark greyish-brown. The surface is densely verruculate.
Male Flowers
Male flowers fuse upward into longitudinal chains. Otherwise, each flower carries 3–5 stamens. Stamens measure 1–1.3 mm in diameter and approximately 0.7 mm in length. They are rounded, oval or irregular in cross-section, and white. Filaments are absent or nearly so, and entirely connate. Anthers are truncate. Pores are apical, rounded or elongate, and confluent.
Fruit
The infructescence is short and cylindric-fusiform, reaching up to 10 cm long and 7 cm in diameter. Berries are elongate and slightly conic, reaching up to 1.8 cm long and 1 cm in diameter near the base. Their apex is truncate. Color is orange-red at maturity, and each berry is single-seeded.
(Photos: Peter Boyce)
Distribution of Amorphophallus infundibuliformis
Amorphophallus infundibuliformis occurs in West Kalimantan (Indonesia) and in East Malaysia (Sarawak). Its distribution thus spans the international border that divides the island of Borneo between Indonesia and Malaysia.
For verified occurrence data and distribution records, refer to GBIF – Amorphophallus infundibuliformis and the Plants of the World Online (POWO) – Kew.
Habitat
This species grows exclusively on sandy peat podzols at altitudes of 250–975 m. It occurs under moist to perhumid hill to upper-hill mixed dipterocarp forest at lower altitudes, transitioning to oak-dipterocarp forest at higher elevations. In both cases, the underlying substrate is sandstone. This strict association with sandy peat podzols over sandstone makes A. infundibuliformis one of the more ecologically specialized Bornean aroids (pers. comm. P. Boyce).
Taxonomic Notes
Amorphophallus infundibuliformis holds a unique position in the genus. No other species in the entire genus carries uncinate (hook-shaped) staminodes on the lower portion of its appendix. Consequently, this single character immediately identifies the species without the need for comparison with any other taxon. Furthermore, its funnel-shaped spathe with a very widely acute limb and its strongly ridged spathe base interior add additional diagnostic value. Together, these features make A. infundibuliformis one of the most morphologically distinctive members of the Bornean aroid flora.
Photo Reference
(Photos: Peter Boyce)
References
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- Hetterscheid, W.L.A., Dearden, A. & Vogel, A. (1994). Amorphophallus infundibuliformis Hett., A. Dearden & A. Vogel. In: Blumea 39: 259.
- Kew Science. Amorphophallus infundibuliformis Hett. et al. – Plants of the World Online. Available at: https://powo.science.kew.org/
- GBIF Secretariat. Amorphophallus infundibuliformis occurrence data. Global Biodiversity Information Facility. Available at: https://www.gbif.org/