Amorphophallus hirsutus: The Bristled Aroid of West Sumatra and the Andaman Islands
One feature immediately sets Amorphophallus hirsutus Teijsm. & Binn. apart from nearly all its relatives: the upper portion of its appendix carries dense, short bristles — a character found in virtually no other species in the genus. Teijsmann and Binnendijk formally described it in 1862 in the Natuurkundig Tijdschrift voor Nederlandsch-Indië. This distinctive aroid grows in a variety of disturbed habitats across West Sumatra and the Andaman Islands of India. Its deep maroon-purple inflorescence, pale purplish appendix, and striking leaf markings make it both scientifically interesting and visually compelling. This article introduces A. hirsutus to botanists, naturalists, and plant enthusiasts seeking to understand the breadth of the Amorphophallus genus.
Taxonomic Identity of Amorphophallus hirsutus
Amorphophallus hirsutus belongs to the family Araceae. Teijsmann & Binnendijk described it in Natuurk. Tijdschr. Ned.-Indië 24 (1862): 332. No synonyms are currently recognized for this species.
Morphological Description
Tuber and Leaf
The tuber of Amorphophallus hirsutus is depressed-globose, reaching up to approximately 12 cm in diameter and 8 cm in height. It is dark brown and produces no offsets. The plant normally bears a single solitary leaf, though two leaves occasionally develop together.
The petiole reaches up to about 100 cm in length and approximately 4 cm in diameter. Its surface is largely smooth, though the base sometimes becomes slightly rugose. The background color is bright pale green. Near the base, the surface is almost entirely covered by tiny blackish-green dots. These dots become slightly or distinctly larger and whitish higher up the petiole. Toward the end of the growing season, the petiole top transforms into an intercalary bulbil.
The lamina reaches approximately 1 m in diameter and is highly dissected. Its rachises carry wings throughout their length, though these wings narrow toward the bases. Leaflets are elongate-elliptic, 7–35 cm long and 2.5–7 cm wide, and acuminate at the tip. In seedlings, the lamina divides into 5–7 parts. Young plants may carry leaflets with a purplish flush or shimmer and bright lilac-purple margins. However, these purplish tones disappear as the plant matures.
Inflorescence and Peduncle
The inflorescence of Amorphophallus hirsutus is solitary and short-peduncled. The peduncle measures 4–10 cm long and approximately 1 cm in diameter. It is plain green or carries a few scattered whitish ring-like spots. In fruit, the peduncle greatly elongates, reaching up to approximately 35 cm.
Spathe
The spathe is campanulate and broadly triangular-oval, 14–25 cm long and 16–29 cm in diameter. It is acute at the apex and slightly constricted between the base and the limb. The margin is undulate. Externally, the base is plain green or carries small blackish spots. The outer limb surface is dark purplish-brown. Internally, the limb and base surfaces match the exterior, though slightly glossier and paler toward the base. The inner base surface is dark maroon and ridged-verrucate, with verrucae in a ridge-like arrangement.
Spadix and Floral Zones
The spadix of Amorphophallus hirsutus is sessile and shorter than the spathe, measuring 8–22 cm in length and approximately 1 cm in diameter. The female zone is nearly cylindric, 1.5–6 cm long and approximately 2.5 cm wide. Its flowers are congested or slightly distant. The male zone is strongly obconic, 2–6 cm long, 0.7–1 cm in diameter at the base, and 2–4 cm at the top. Flowers in the male zone are congested.
The appendix is 4–10 cm long and 4–10 cm in diameter. Its lower portion is subglobose, wrinkled, and rugulose-areolate. The upper portion abruptly attenuates into a truncate, cylindric to conic knob. This knob carries a dense covering of short bristles 1–2.5 mm long — the character that gives the species both its name and its most reliable diagnostic feature. The overall appendix color is pale purplish.
Female Flowers
Each ovary is depressed-globose and more or less angulate in cross-section. It measures 3–3.5 mm in diameter and 2–2.5 mm tall. Each ovary is 2–3-locular, pale green, with a maroon upper portion. The style is slender, 6–7 mm long and 1.2–1.3 mm in diameter, and maroon. The stigma is large and oval in cross-section, cordate in longitudinal section, measuring 3 × 2 mm and approximately 2 mm tall. It is dirty greyish and strongly 2- or 3-lobed, with conic, acutish lobes that often diverge. The surface is verruculate.
Male Flowers
Each male flower carries approximately 4 stamens. Stamens reach approximately 2 mm in length. Filaments are 0.1–0.3 mm long and connate. Anthers measure 1.7–1.9 mm long and 1.5–2.5 mm in diameter, dirty yellowish-white in color. The connective is broad and slightly to strongly raised, sometimes carrying a short conical process. After anthesis, a longitudinal groove appears on the connective. Pores are apical and elongate.
Fruit
The infructescence is long-peduncled, with a cylindric fruiting portion bearing distant berries. Berries are ovate and orange-red.
Distribution of Amorphophallus hirsutus
Amorphophallus hirsutus occurs in West Sumatra, Indonesia, and in the Andaman Islands of India. This disjunct distribution — spanning both the Malay Archipelago and the Indian Ocean island chain — makes it one of the more biogeographically interesting members of the genus.
For verified occurrence data and georeferenced records, refer to GBIF – Amorphophallus hirsutus and the Plants of the World Online (POWO) – Kew.
Habitat
This species grows in disturbed areas, on limestone substrates, in field yards, and in secondary forest. Its tolerance for multiple disturbed habitat types distinguishes it from many more ecologically specialized relatives. Furthermore, its capacity to colonize limestone and field margins suggests broad ecological plasticity for a species of relatively limited geographic range.
Taxonomic Notes
Amorphophallus hirsutus resembles A. paeoniifolius in overall inflorescence shape. Both species share a similar campanulate spathe form and a broadly expanded appendix structure. Nevertheless, one character immediately separates them: A. hirsutus carries dense short bristles on the apex of its appendix knob. A. paeoniifolius entirely lacks this feature. Consequently, any specimen displaying a bristled appendix apex belongs to A. hirsutus rather than its morphological counterpart.
Photo Reference
References
- Teijsmann, J.E. & Binnendijk, S. (1862). Amorphophallus hirsutus Teijsm. & Binn. In: Natuurk. Tijdschr. Ned.-Indië 24: 332.
- Kew Science. Amorphophallus hirsutus Teijsm. & Binn. – Plants of the World Online. Available at: https://powo.science.kew.org/
- GBIF Secretariat. Amorphophallus hirsutus occurrence data. Global Biodiversity Information Facility. Available at: https://www.gbif.org/
