Amorphophallus muelleri: The Bulbil-Bearing Aroid of Southeast Asia
Among the most widely distributed and economically significant aroids in the Indonesian archipelago, Amorphophallus muelleri Blume commands attention for multiple reasons. Blume formally described it in 1837 in the Rumphia. Its range stretches from Sumatra and Java through Kalimantan, Flores, Timor, and the Andaman Islands to Myanmar and northern Thailand. Farmers in East Java cultivate it intensively for the glucomannan contained in its tubers. Botanists value it for its unique leaf-borne bulbils, which no other Indonesian species produces. And collectors prize it for its dramatic, broadly triangular spathe patterned with creamy white spots. A. muelleri is also a triploid (3n = 39) that sets pseudoseeds without pollination, making it biologically unusual within the genus.
Taxonomic Identity of Amorphophallus muelleri
Amorphophallus muelleri belongs to the family Araceae. Blume described it in Rumphia 1 (1837): 143. Several synonyms exist for this widely collected and reclassified species:
- Amorphophallus blumei (Schott) Engl. [illegitimate]
- Amorphophallus burmanicus Hook.f.
- Amorphophallus carnosus Engl.
- Amorphophallus erubescens Hett.
- Amorphophallus oncophyllus Prain ex Hook.f.
- Amorphophallus planus Teijsm. & Binn.
- Amorphophallus timorensis Alderw.
- Amorphophallus muelleri (Blume) Schott
- Conophallus blumei Schott [illegitimate]
- Conophallus muelleri (Blume) Miq.
- Conophallus planus (Teijsm. & Binn.) Miq.
Many Indonesian growers still use the name A. oncophyllus (a synonym) rather than the accepted name A. muelleri.
Morphological Description
Tuber and Leaf
The tuber of Amorphophallus muelleri is globose to depressed-globose, dark brown on the outside, and yellow to orange inside. It reaches up to 28 cm in diameter and weighs up to approximately 3 kg. It develops no annual offsets. The root scars are annuliform and swollen. The plant normally bears a single solitary leaf, though occasionally two leaves emerge from one tuber.
The petiole is smooth, 40–180 cm long, and 1–8 cm in diameter at the base. Its color ranges from green and olive-green to brownish-green or almost black. The surface carries numerous large, elongate-elliptic, diamond-shaped or stripe-like pale green spots, and sometimes also numerous small, pale green rounded dots. The lamina is highly dissected, 75–200 cm in diameter. In the center, it carries epiphyllar bulbils on the major branchings and on the most distal branches. These leaf-borne bulbils are depressed, rounded or elongate, greyish-brown, 0.5–6 cm in diameter, and number 1–40 per leaf.
Leaflets are elongate-elliptic to narrowly elongate-elliptic, acuminate, with a strongly and broadly decurrent base. They measure 10–40 cm long and 4–15 cm in diameter. The upper surface is green to dark green with a narrow, whitish or pinkish-red margin, especially in young plants. Seedling leaflets are dark emerald green with a reddish flush and strong red margins.
Inflorescence and Peduncle
The inflorescence of Amorphophallus muelleri is solitary and long-peduncled. The peduncle shares the same appearance as the petiole, measuring 30–60 cm long and 0.5–3 cm in diameter at the base.
Spathe
The spathe is broader than long, or rarely slightly longer than wide. It is very broadly triangular or transversely elliptic, coriaceous, and marcescent, measuring 7.5–32 cm long and 6–36 cm in diameter. The base is strongly convolute and slightly to clearly constricted at the top. The limb is semi-erect to spreading, often partly horizontal. The margin is reflexed and somewhat suddenly narrowed to the top, where it becomes very obtuse.
The interior base surface is nearly smooth or carries numerous small, elongate warts. These warts are often confluent. The outer base surface is pale green or pale dirty pinkish with usually transversely elongate whitish spots and a few small blackish-green dots. Upward, the outer surface grades to brownish-purple, pink, or dark greyish-green with large, approximately iso-diametrical white spots. The inner base surface is dark pink, bright pale pink, or pale yellowish pink, grading upward to purplish, pink, dark pink, dark brownish-pink or brownish. The uppermost inner zone is dirty pale greenish and dirty pale brown with transversely oval spots, or the latter with dirty pale greenish background.
Spadix and Floral Zones
The spadix of Amorphophallus muelleri is sessile to stipitate or intermediate, and longer than the spathe. It measures 8–40 cm in length. The stipe, when present, is 0.1–1.5 cm long and dries in fruit. The female zone is cylindric to slightly fusiform, 1.5–10 cm long and 1–5 cm in diameter. Flowers are congested, lax, or intermediate. The lowermost flowers are more loosely arranged than the upper ones.
The male zone is cylindric, obconic, or fusiform, 2–9 cm long and 0.9–6 cm in diameter. In large specimens, it is usually laterally compressed. Flowers in the male zone are congested. The appendix is thick-walled and fusiform-conic, subacute to acute at the apex. It is laterally compressed to various degrees, with numerous small punctiform depressions and some irregular larger shallow depressions. The base area between the stamens and the appendix wall carries staminodes. The appendix measures 3–22 cm long and 1.5–9 cm in diameter, pale pinkish, yellowish, or pale brownish. It develops an offensive scent described as resembling durian or old cabbage. Flowers are unisexual but occasionally intermediately bisexual with a reduced pistil surrounded by few stamens.
Female Flowers
Each ovary is shortly stipitate and depressed, 3–3.5 mm in diameter and 1–1.5 mm tall. The lower half is reddish-purple and the upper half is pale pink. Each ovary is 2–3-locular, with one basal ovule per locule. The stipe is approximately 0.5 mm long. The style is short and thick, largely pale pink, but with a reddish-purple uppermost zone, measuring 0.3–1 mm long and 0.8–1 mm in diameter. The stigma is large but always slightly smaller in diameter than the ovary. The color is dirty pale yellow. It measures 1–2 mm in diameter and 0.8–1.5 mm tall. The surface is micro-rugose or micro-scabrate to echinate and copiously coated with a very sticky, viscous fluid.
Male Flowers
Each male flower carries 3–5 stamens. Anthers are sessile, elongate, irregularly prismatic or rectangular in cross-section, and truncate. They are dirty pale yellow, 1–2 mm long and 0.8–2 mm in diameter. Pores are apical, small, elongate, and oval at anthesis. Most thecae contain an amorphous mass at anthesis, with only a few extruding a very small amount of whitish material.
Fruit and Seed
The infructescence is cylindric and can contain up to 1,000 berries. Berries are elongate to elongate-ovate, with a slightly depressed apex, measuring 1.2–1.8 cm long. They ripen from green to bright red, and each carries 2 or 3 seeds.
Distribution of Amorphophallus muelleri
Amorphophallus muelleri grows across a broad geographic range in Southeast Asia. It occurs in Sumatra, Java, South Kalimantan, Flores, and Timor Timur in Indonesia, and extends through the Andaman Islands, Myanmar, and northern Thailand. This broad distribution — from the Indian Ocean islands to mainland Southeast Asia — makes it one of the most range-extensive members of the genus.
For verified occurrence data and georeferenced records, refer to GBIF – Amorphophallus muelleri and the Plants of the World Online (POWO) – Kew.
Habitat
This species grows in thickets, disturbed areas, forest edges, and village groves, at approximately 900 m altitude. Its preference for disturbed and semi-open habitats over closed primary forest helps explain its wide distribution and its long history of association with human agricultural landscapes.
Taxonomic Notes
Amorphophallus muelleri is easy to recognize in flower by three characters acting together. First, the spathe is constricted at the top. Second, the lower inner surface of the spathe is pink. Third, the stigmas are notably large and 3–4-lobed. In the vegetative state, the epiphyllar bulbils on the leaf rachises immediately separate it from all other Indonesian species in the genus — no other Indonesian Amorphophallus produces these leaf-borne bulbils.
Furthermore, A. muelleri is a confirmed triploid (3n = 39). It sets pseudoseeds without pollination, making seed production independent of pollinators. Consequently, it propagates readily from both its abundant leaf bulbils and from seed. Farmers in East Java have exploited this characteristic, cultivating the species intensively for the glucomannan in its tubers. However, many local growers and markets in Indonesia still refer to the species by the synonym A. oncophyllus rather than the accepted name A. muelleri.
Photo Reference
References
- Blume, C.L. (1837). Amorphophallus muelleri Blume. In: Rumphia 1: 143.
- Hetterscheid, W.L.A. & Ittenbach, S. (1996). Everything you always wanted to know about Amorphophallus, but were afraid to stick your nose into! Aroideana 19: 7–131.
- Kew Science. Amorphophallus muelleri Blume – Plants of the World Online. Available at: https://powo.science.kew.org/
- GBIF Secretariat. Amorphophallus muelleri occurrence data. Global Biodiversity Information Facility. Available at: https://www.gbif.org/
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