Timonius arabii (Rubiaceae: Guettardeae), a new species from Bau limestone, Sarawak, with notes on its pollination ecology

Our understanding of the pollination ecology of Timonius (a dioecious genus) is limited to deducing their pollination syndrome based on floral traits. Through a series of field surveys on several populations of Timonius as a prerequisite to studying their pollination ecology, a new species from a limestone hill in northern Dered Krian National Park in Bau, Sarawak, Malaysia is described. The new species, Timonius arabii, and two other co-occurring congeners were compared in terms of morphology and ecology, in relation to the unique site conditions. Timonius arabii is associated with phalaenophily, as inferred from its yellow, short tubular, faintly fragrant, nectar-producing flowers which open around dusk in both staminate and pistillate individuals. The anthetic period in male flowers typically spans only one night but may last 2-3 days in female flowers. Floral visitors monitored from dusk to dawn over a 7-day observational period show that the flowers attracted up to 23 floral visitor types/species belonging to Coleoptera, Thysanoptera, Lepidoptera, Diptera and Orthoptera, with most species belonging to moths. Two geometrid moths, Eumelea biflavata and E. florinata, have the highest visitation rate to female flowers, probably indicating their role in the pollination of the species. Further study is needed to demonstrate this, while also not excluding the potential role of other moth species as well as thrips and weevils as pollinators. Our preliminary observation provided important baseline data needed for a better understanding of the plant-pollinator relationships in Timonius.