Seed morphology in Euphorbia and its taxonomic applications: a case study in Sao Paulo, Brazil

Abstract

Euphorbia L., with around 2000 species, is the biggest genus of Euphorbiaceae and one of the largest and most diverse genera within Angiosperms. It shows an almost cosmopolitan distribution and notable morphological diversity and is characterized by a pseudanthial inflorescence, the cyathium, which is unique to the genus. Along with its great morphological diversity in growth form, seed characters such as shape, testa ornamentation and presence or absence of caruncle are among its most notable and variable features. Given the potential utility of seed characters for species identification, we set to characterize the seeds from all known species (24) of Euphorbia occurring in the state of Sao Paulo, using photos and scanning electronic microscopy images. These species belong to three subgenera and seven sections of Euphorbia, and their morphological diversity is discussed in a phylogenetic context according to the most recent classification. Seed characters such as shape, size, testa ornamentation, and presence or absence of caruncle proved to be useful for identification of sections and for distinguishing closely related species.