Plethiandra sahebii, a new Melastomacea from Sarawak, described
I.H. Burkill’s 1917 description of Plethiandra sahebii presents a new species of Melastomataceae from Sarawak, described from a single living specimen in cultivation at the Singapore Botanic Gardens. The article’s central contribution is a morphologically detailed account of the species—uniquely illustrated from life rather than dried material—alongside a comparative analysis of floral dimensions across the genus and a brief systematic discussion of its affinities to Medinilla and Carionia.
Summary
Burkill’s description arises from a practical taxonomic problem: the genus Plethiandra, established by Hooker in 1867 from a single “rather poor specimen” collected by Motley in Sarawak, had remained poorly understood for decades. Subsequent authors—Baillon, Krasser, Cogniaux—had been unable to add meaningful information, and even Stapf’s 1894–1896 work, which expanded the genus to seven species and reduced Cogniaux’s Medinilopsis into it, relied on dried specimens that could not resolve the positions of stamens and stigma in the flower. Burkill’s opportunity came through a single individual brought to the Singapore Botanic Gardens in 1907 by a former employee, B. K. Saheb, from the forests near Kuching. Because the plant was available alive and in flower, Burkill could produce a figured description from life, resolving ambiguities that had persisted since Hooker’s original treatment.
The description itself is notably detailed for a single-specimen account. Burkill documents the plant’s cauliflorous habit—flowers arising from persistent axillary cushions on old leaf scars, continuing to produce blooms indefinitely after the leaf has fallen—its dichotomous branching pattern, and the development of adventitious rootlets at the nodes that ultimately cause the plant to flower among its own roots. The floral morphology is the article’s technical core: six contorted petals, approximately 28 stamens directed to the upper side of the horizontal flower, a decurved style 9 mm long, and a very concave receptacle. Burkill provides a Latin diagnosis and a full protologue with collection data.
The article closes with a comparative and systematic discussion. Burkill tabulates calyx, petal, and stamen dimensions across all seven known species, showing P. sahebii to be intermediate in size—smaller than the outstanding P. beccariana but larger than several others. He notes that the petals are consistently six in number, that the ovary is almost always six-locular (contradicting Hooker’s and Cogniaux’s earlier counts of four and three), and that the apical pore of dehiscence appears constant. He aligns the genus with Medinilla following Stapf, and notes the close affinity of the Philippine genus Carionia, while distinguishing it by stamen number and flower size.
Key Findings
- The type specimen is a single individual collected in 1907 from the forests near Kuching, Sarawak, by B. K. Saheb, and maintained in cultivation at the Singapore Botanic Gardens (p. 268).
- The plant is a glabrous shrub approximately one metre high, dichotomously branching from four basal stems to sixteen leafing branches, with leaves reaching 30 cm × 12 cm (pp. 266–267).
- Floral dimensions: calyx 3 mm, petals up to 6 mm, filaments 3 mm, anthers 2 mm, style 9 mm, receptacle very concave; stamens almost constantly 28 in number (pp. 267–268).
- The genus Plethiandra was originally described by Hooker in 1867 from a single poor specimen; Stapf expanded it to seven species by 1896, reducing Cogniaux’s Medinilopsis into it (p. 265).
- Comparative floral data show P. beccariana as the most outstanding species (calyx 6 mm, petals 10 mm, stamens 10–12 mm, pedicels to 2 cm), while P. sahebii is intermediate (p. 268).
- Burkill argues the ovary is consistently six-locular across the genus, contradicting Hooker’s count of four for P. motleyi and Cogniaux’s count of three for Medinilopsis (p. 268).
Conclusion
Burkill’s definitive contribution is the establishment of P. sahebii as the eighth species of the genus, described with a level of floral detail—particularly the stamen and stigma positions in the horizontal flower—that was previously unattainable from dried material. The article simultaneously corrects earlier errors in the genus’s morphology (locule number, stamen variability) and reinforces Stapf’s systematic placement of Plethiandra in the neighbourhood of Medinilla, with Carionia as a close ally distinguished by smaller stamen numbers and larger flowers.
Context
- The description is based entirely on a single living specimen in the Singapore Botanic Gardens collection, with no herbarium material cited; the plant “has no horticultural value” and was grown solely for determination (p. 266).
- The article represents a standard early-20th-century taxonomic monograph of a single new species, contributing to the ongoing revision of Bornean Melastomataceae initiated by Hooker, Cogniaux, and Stapf.