A TAXONOMIC AND BIOGEOGGRAPHIC ASSESSMENT OF TIMONIUS DC. (RUBIACEAE) IN KINABALU PARK, BORNEO

Abstract

Kinabalu Park is a centre of plant diversity in Borneo. The geologically diverse and isolated Kinabalu massif arguably has the richest flora globally. Nonetheless, certain plant taxa such as Timonius remain poorly studied. The most recent floristic account recognises nine Timonius species whereas recent ecological collections appeared to represent 15 species. This study is conceived to revise the Kinabalu Timonius and attempt a rarity assessment. Comparative study of herbarium sheet specimens and microscopy studies of the leaf lower lamina surface were conducted. Species were recognised based on discontinuous patterns in morphological variation. This study recognises 15 Timonius species in Kinabalu Park, comprising four named species and 11 putative new species. Nine species are likely to be endemic to Kinabalu Park. Distinct hair types on the lower lamina surface are useful for distinguishing species. Also, the distribution of some Timonius species is possibly constrained by ultramafic substrates. Useflil perspectives towards potentially understanding speciation in Timonius on mountain habitats and reasonable approaches for a wider phylogenetic investigation of Timonius in Borneo are discussed. This study revealed diagnostic characters for recognising the Kinabalu Timonius and suggests that tropical plant diversity may be underestimated in areas such as Borneo.