Abstract
Astraea is a genus with 13 species, widely distributed throughout Neotropics and especially diverse in Brazil. The genus is currently placed in Crotoneae as sister to Acidocroton. This work aimed to characterize the pollen of Astraea as a contribution to the taxonomy and to understand the evolution of pollen traits between Astraea and Acidocroton. Pollen grains of 12 species of Astraea and three of Acidocroton were gathered from herbarium specimens, acetolyzed, measured, photographed and described under light microscope and scanning electron microscopy. Our results demonstrate that Astraea is a stenopolinic (stenopalynous) genus with pollen grains that are apolar, spherical, medium to large, inaperturate, showing a Croton pattern exine with sexine thicker than nexine, and with rosettes having clavae or pila in their lumen. The rosettes consist of 5-7(-8) pila that can be rounded to triangular with psilate to plicate surface. Pollen features did not reveal synapomorphies for Astraea, Acidocroton or even for the Astraea + Acidocroton clade. Several pollen features evolved independently among recent lineages of Astraea, and we interpreted these evolutionary shifts as adaptations to new habitats. This work consolidates the palynological knowledge of Astraea and Acidocroton and will contribute to future palynological and systematic studies in Euphorbiaceae.
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Acknowledgements
The authors are grateful to Fundação de Amparo à Pesquisa dos Estados da Bahia (FAPESB) and São Paulo (FAPESP) for the scholarship awarded to LRS (#2018/3046) and OLMS (#2013/26501-6 and #2017/06171-2), respectively; to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support to FARS (#302594/2016-7) and IC (#309917/2015-8); to the curator of the visited herbaria for providing access to their collections; and to the Laboratório de Palinologia from Universidade do Estado da Bahia—Campus VII.
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de Souza, L.R., Carneiro-Torres, D.S., da Silva, O.L.M. et al. Pollen morphology and evolution in Astraea (Euphorbiaceae: Crotoneae). Plant Syst Evol 306, 55 (2020). https://doi.org/10.1007/s00606-020-01683-7
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DOI: https://doi.org/10.1007/s00606-020-01683-7