Spolia mentawiensia: Pteridophyta
R.E. Holttum’s 1928 paper “Spolia Mentawiensia: Pteridophyta” presents a taxonomic treatment of the fern and allied plant flora collected on the Mentawai Islands of Siberut and Sipora during a 1924 expedition led by C.B. Kloss. The work documents 77 species across both islands, describes two new species to science, and extends the known geographic ranges of several taxa with significant biogeographic implications for the Malay Archipelago.
Summary
The paper is a standard floristic treatment of pteridophyte specimens gathered by Kloss and his local collector Iboet during their 1924 fieldwork on the two largest Mentawai islands. Holttum organises the 77 species according to Christensen’s Index Filicum nomenclature, spanning the Psilotales, Lycopodiales, and Filicales. The majority of species are of wide distribution across the Malaysian region, and Holttum is candid that the collection does not represent a complete record of the local flora, noting the absence of universal species such as Gleichenia linearis (p. 14).
The substantive contributions lie in the treatment of four taxa of particular interest. First, Lygodium borneense is discussed at length in light of the Mentawai specimens alongside recent Bornean collections in the Buitenzorg Herbarium; Holttum demonstrates that the variation in secondary petiole branching (from once-forked to multiply-forked) is continuous and that van Alderwerelt’s forma samarindae does not represent a discrete entity (pp. 15–16). He further notes the species’ remarkable absence from the lowlands of Sumatra and the Malay Peninsula, suggesting it may have been overlooked due to resemblance to L. cinnatum in smaller forms. Second, Trichomanes aphlebioides, originally described from New Guinea, is shown to occur on both Mentawai islands with well-developed aphlebiae (sterile, highly branched fronds) up to 11 cm in length, extending its known range considerably (p. 17).
Two new species are formally described: Alsophila parvifolia, a small tree fern from Siberut and Sipora that Holttum identifies as the only recorded example of a simply pinnate Alsophila from Malaysia, comparable in size to the Peruvian A. phegopteroides (p. 18); and Polypodium papilliferum from Sipora, distinguished by its very narrow ciliate scales and sharply acute soral papillae (p. 21).
Key Findings
- 77 pteridophyte species recorded in total: 59 from Siberut, 29 from Sipora (p. 14).
- Two new species described: Alsophila parvifolia (Siberut, Kloss 14579; Sipora, Iboet 554) and Polypodium papilliferum (Sipora, Kloss 14800) (pp. 18, 21).
- Lygodium borneense range extended to the Mentawai Islands; Holttum demonstrates that the previously recognised forma samarindae is not a discrete taxon but part of a continuous variation series in secondary petiole branching (pp. 15–16).
- Trichomanes aphlebioides range extended from New Guinea to the Mentawai Islands and confirmed from Gunong Panti, Johore (Ridley 4147); aphlebiae observed up to 11 cm in length with distinctly winged main branches (p. 17).
- Microlepia Ridleyi (Copeland) confirmed from Sipora (Kloss 14659); Holttum argues that older Peninsula collections identified as M. Kurzii (Clarke) should be reinterpreted as a hairy form of M. platyphylla (Don), and that M. puberula v.A.v.R. from Java may be identical to M. Ridleyi (p. 21).
- Hemitelia sumatrana v.A.v.R. collected from Siberut (Kloss 12284; Iboet 42) but lacking the very copious ferruginous hairs on rachis and costae that characterise the species (p. 18).
Conclusion
Holttum’s definitive takeaway is that the Mentawai pteridophyte flora, while largely composed of widely distributed Malaysian species, contains elements of considerable biogeographic interest—particularly the presence of Lygodium borneense, a species previously known only from Borneo, and the two new species that fill gaps in the regional flora. The paper underscores that the Mentawai Islands, though geographically close to Sumatra, harbour a distinct assemblage that warrants further investigation.
Context
- The specimens derive from the 1924 Kloss expedition to the Mentawai Islands; type material is deposited in the Raffles Museum, Singapore, and comparative material was examined at the Buitenzorg Herbarium (Bogor) and Kew (p. 14, 15, 21).
- The paper is part of the broader “Spolia Mentawiensia” series documenting the flora of the Mentawai Islands, a project that contributed to the systematic botanical survey of the Malay Archipelago during the colonial period.