Pollen morphology and exine ultrastructure of Brasiliocroton P.E. Berry & Cordeiro (Euphorbiaceae)

Abstract

The present study aimed to morphologically characterize the pollen grains of species of Brasiliocroton mamoninha and B. muricatus in order to expand palynological knowledge of the group and provide additional micromorphological information useful for studies of the relationships within Crotoneae. Polleniferous material was acetolysed and described using light, scanning electron and transmission microscopy. The pollen grains of the two species of Brasiliocroton were apolar, spherical, inaperaturate and medium-sized with a Croton ornamentation pattern. The Croton pattern of B. mamoninha is formed by subtriangular pila, >5-plicate with pointed apices, while for B. muricatus it is formed by subcircular to circular pila, <5-plicate with rounded apices. Ultrastructural analysis revealed a stratified sexine in both species, whereas variation in the pattern of deposition of the foot layer allowed the species to be palynologically distinguished from each other. The composition of the Croton pattern of ornamentation, the morphology of the ultrastructure of the wall and the range of variation in the diameter of the pollen grains differed between the studied species, and thus are diagnostic characters. Pollen morphology allowed the two species of Brasiliocroton to be palynologically separated, and provided data that will be useful for taxonomically circumscribing these taxa.

Pollen morphological characters variation among species of Strobilanthes s.l. from Sumatra, Indonesia and its taxonomic implications

“…The pollen morphological characters have been widely used in various plant groups of Angiosperms (Telleria et al 2013;Al-Hakimi et al 2015;Zhao et al 2016;Mander 2016;Kriebel et al 2017;Silva et al 2017;Xiong et al 2019;Raza et al 2020). They can be used to solve the taxonomic problems of plant groups, such as identification, taxa delimitation, classification and relationship assessment (Yao and Zhang 2016;Al-Hakimi et al 2017;Tripathi et al 2017;Ruiz-Domínguez et al 2019;Chen et al 2019;de Souza et al 2019;Ragho 2020). The pollen morphological characters such as polar axis length (P), equatorial diameter (E), P/E ratio, pollen sculpture or exine ornamentation (Via do Pico and Dematteis 2013;Ferrauto and Pavone 2014;Sarwar et al 2015;Al-Hakimi et al 2018), pollen size, pollen shape, exine thickness (Akhila and Beevy 2015;Krachai and Pornpongrungrueng 2015;Noedoost et al 2021) are valuable for distinguishing and identification of many plant groups.…”