Preliminary study on variations in local varieties of bornean ironwood (Eusideroxylon zwageri Teijsm. & Binn.) based on vegetative characters

Abstract

Bornean Ironwood (Eusideroxylon zwageri), a monotypic species of Eusideroxylon, is threatened due to its rarity in its natural habitat. It is a Class I timber commodity in Indonesia and known with several local varieties determined by local people. This study aimed to described the local varieties of ironwood from Kalimantan by taxonomic study. Field exploration had been carried out during 2022 to 2023 in North Kalimantan, East Kalimantan, and West Kalimantan provinces to collect herbarium specimens of ironwood local varieties. The specimens were then observed and characterized in Laboratory of Plant Biosystematics-BRIN. Observation was also done for ironwood collection available at Herbarium Bogoriense. Fourty one characters extracted from vegetative parts, such as stems, twigs and leaves were used to find clades within ironwood species. Phenetic analysis generated six clades in which hair characters on twigs and leaves and color variations of twigs and petiole were the main informative characters that differentiate between clades at an infraspecific level. Anatomical characters cannot be used as supporting characters in this study. Support from deeper morphological analysis involving more specimens and species groups affiliated with the genus Eusideroxylon, as well as molecular analysis is needed to strengthen the grouping at an infra-specific level.