Begonias of Borneo
H. N. Ridley, Director of the Singapore Botanic Gardens, published this taxonomic treatment of Bornean Begonia species in 1906, describing sixteen new species and revisiting several previously known taxa from Sarawak and the broader island. The article establishes that Borneo—particularly the limestone karst of Sarawak—harbours a notably rich and under-described begonia flora, with the Petermannia section dominating the tall woodland forms and a distinct assemblage of small rhizomatous and epiphytic species colonising cave mouths and rock faces.
Summary
Ridley’s central concern is the floristic poverty of the Bornean begonia literature relative to the actual diversity present in the field. He opens by observing that the tall woodland species of the Petermannia section are the most abundant but also the most difficult to delimit, owing to considerable intraspecific variability and the probable occurrence of hybridisation. He notes that the presence or absence of petals in male flowers—a character frequently relied upon in earlier classifications—is unreliable, as he has observed the same plant bearing flowers with none, one, or two petals (p. 247). This observation frames the entire paper as a corrective to the over-reliance on a single morphological character in begonia taxonomy.
The body of the article proceeds as a series of formal species descriptions, each accompanied by a diagnostic key at the outset that sorts the twenty-one species into three sections: Petermannia (tall-stemmed, three-winged capsules), Bractibegonia (short-stemmed or rhizomatous, often with prominent bracts), and Platycentrum (epiphytic, with a single large capsule wing). Ridley draws heavily on specimens collected by Dr. W. J. Haviland, Mr. Hullett, and himself from localities across Sarawak—Matang, Bau, Niah, Jambusan, the limestone caves of Bidi and Braang, and the sandstone cliffs of Bukit Tendong near Busan—as well as material from Kinabalu in British North Borneo. Several species are named after collectors or associates: B. Pryeriana after Mr. Pryer of Byte Estate, B. Hullettii after Hullett, and B. Havilandii after Dr. Haviland (pp. 252–259).
A recurring ecological theme is the association of the smaller, more ornamental species with limestone substrates. B. speluncae, with its tufts of round leaves and white flowers, grows abundantly in cave mouths; B. promethea clings flat to the vertical sandstone faces of Bukit Tendong; B. rubida and B. pendula are both recorded from the Jambusan limestone caves. Ridley singles out B. promethea as “perhaps the most worthy of cultivation” among the foliage plants, noting that two specimens he brought to Singapore flowered readily in December and January (p. 259).
Key Findings
- Sixteen new species are described: B. axillaris, B. propinqua, B. sarawakensis, B. Pryeriana, B. congesta, B. polygonoides, B. pubescens, B. Hullettii, B. elatostemma, B. rubida, B. pendula, B. speluncae, B. Havilandii, B. promethea, B. Pyrrha, and B. calcarea (pp. 249–261).
- B. Burbidgei (Stapf), collected at 7,600 feet on Kinabalu, is identified as the largest-flowered begonia known from Borneo, with white flowers 1½ inches across (p. 256).
- B. inostegia (Stapf), known only from Kinabalu at 6,000 feet elevation, is distinguished by stipules broken up into long fibres at the tip (p. 253).
- B. oblongifolia (Stapf) is recorded as the commonest species in Sarawak, occurring at Matang, Bau, Puak, Jambusan, Lundu, and Sepudang, with notable variation in leaf form between localities (p. 252).
- B. promethea grows with only two or three large leaves pressed flat against vertical sandstone rock faces at Bukit Tendong near Busan; specimens transplanted to Singapore flowered within months (p. 259).
- B. calcarea, known from a single specimen with one capsule and no flowers from the top of Mount Braang, is described with the explicit caveat that it is “hardly sufficient to describe” (p. 261).
Conclusion
Ridley’s definitive takeaway is that Borneo’s begonia flora, while already yielding a substantial number of new species in this single paper, remains far from exhaustively documented. The variability within the Petermannia section, the probable hybridisation among tall woodland forms, and the paucity of material for several cave and rock-face species all point to a flora that will yield further novelties as collection effort intensifies in the limestone districts of Sarawak and the high elevations of Kinabalu.
Context
- The primary material derives from the herbarium collections of the Singapore Botanic Gardens, with specimens gathered by W. J. Haviland (Sarawak and Kinabalu), Hullett (Matang), and Ridley himself during fieldwork in Sarawak in the 1890s and early 1900s.
- The article contributes to the early systematic revision of Begonia in Malesia, building on Stapf’s 1896 treatment in the Transactions of the Linnean Society and extending the known range of the genus in Borneo from a handful of described species to over twenty.