Trichomes’ Micromorphology and Their Evolution in Selected Species of Causonis (Vitaceae)

Abstract

The Vitaceae genus Causonis is found in tropical to temperate climates from Asia to Australia, including the Pacific Islands. Rafinesque established the genus in 1930; however, Süssenguth classified it under Cayratia as a sect. Discypharia in 1953. The genus was resurrected in 2013 using morphological and genetic evidence. We herein provided insight into the diversity of trichomes’ micromorphology of selected species of this recently reinstated genus for taxonomical implication. Simple trichomes, representing non-glandular and unbranched trichomes, are only found in Causonis. Trichomes vary from straight, curved, hooked, appressed, pilose, to villous in different parts like branchlets, abaxial leaf surface, and adaxial leaf surface in different species. They also vary in the same plant from the young stage to the mature stage. Most species are pubescent when young, but a few species become nearly glabrous when they are mature. Significant variations can be observed in trichomes’ length between the species. Principal component analysis (PCA), based on the micromorphological traits, was carried out for the species delimitation. In Mesquite, ancestral character state reconstruction was used to examine evolutionary trends for trichomes on three different surfaces. The glabrous to sparsely pubescent state found on the branchlets and both leaf surfaces were found to be the ancestral state and, on the branchlets and both leaf surfaces, the villous hairs state was the derived state in the genus. The identification of Causonis species is greatly aided by trichomes morphology. Therefore, similar studies should be conducted on other Vitaceae genera to reveal the variety of trichomes found in the family.