Pollen morphology of family Thymelaeaceae Juss. in India and its taxonomic implications

Abstract

We provide pollen morphology and ultrastructure of 26 plant taxa, comprising 14 genera, 21 species, 1 sub-species and 3 varieties, of the Thymelaeaceae family from the Indian sub-continent using light micsoscopic (LM) and scanning electron microscopic (SEM) techniques. The principal aim was to provide new and useful information regarding the extent of the pollen morphological diversity among the Thymelaeaceae taxa and, thus, contribute to a better understanding of the taxonomy of the studied taxa. The pollen grains of the studied taxa are essentially radially symmetrical, apolar, (released as) monad, pantoporate with a typical crotonoid pattern, and spheroidal (mostly) in shape; but widespread variations with respect to the number and dispensation of pores, size, exine (ectoexine and endoexine) thickness, and the shape itself (spheroidal, sub-spheroidal and prolate spheroidal), as well as in the amb (outline) have been also recorded. Pollen identification keys, based on the pollen micro-morphological attributes, were also constructed in order to easily identify the 26 studied Thymelaeceae taxa up to species and/or varieties level (high taxonomic resolution, showing taxonomic significance). The pollen morphological attributes of the 26 studied plant taxa of the Thymelaeaceae family were subjected to Principal Component Analysis (PCA) and Hierarchical Component Analysis (HCA), which suggest four clusters. The cophenetic correlation coefficient also validates the four group of clustering. The study will significantly help in the precise pollen identification in fossil (pollen) records for the reconstruction of vegetation dynamics and contemporary climate change during the Quaternary Period in India. Moreover, the present study also helps in determining the phylogenetic and evolutionary trend on the basis of the presence or absence of exine ornamentation and having more or less apertures among the pollen grains of the 26 studied Thymelaeaceae taxa.