Species limits of the endemic genus Stemonoporus Thw. : leaf architecture answers

Abstract

Stemonoporus Thw. is the most species-rich (27 species) endemic dipterocarp genus in Sri Lanka. All its members are categorized as highly threatened or threatened in the IUCN red data book. A recent study carried out in order to evaluate the species limits ofStemonoporus, further strengthened its position as the most species-rich endemic dipterocarp genus in Sri Lanka by further adding a new species and totaling the number to 27. A detailed study on leaf architecture was carried out in order to identify characters for field identification of these 27 species. Leaves were cleared and scored for characters. Twenty leaf architectural characters were identified, including leaf venation type, primary, secondary and tertiary veins, areoles and veinlets. A comprehensive description of leaf architecture for all the species was complied. A combined phylogenetic analysis with other morphological characters was performed. The simple, entire margined, spirally arranged leaves indicated a shared ancestry.

Within the genus Stemonoporus, all 27 species are monophyletic and are supported by leaf architectural apomorphies.

The leaf venation characters used during the previous works are indistinctly defined and during the present study, novel, strong and stable leaf architectural characters were identified for each of the species. These characters could play a crucial role in field identification of these highly threatened taxa.