The seed coat in the evolutionary context of Bromelioideae (Bromeliaceae): Morphoanatomical diversity and ontogeny in the core and tankless lineages

Abstract

Seed morphology could provide significant characters for understanding the diversification of some clades in Bromeliaceae subfamily Bromelioideae, but little is known about the anatomical diversity and ontogeny of the seed coat in this diverse subfamily. We analysed the morphoanatomy of the seed coat for 48 species from 25 genera of the major lineages of Bromelioideae, from which we selected four species for ontogenetic analysis. Standard techniques for light microscopy were adapted for the anatomical study of seeds. Thirty-three variable characters were described and compared. Flattened or angular usually exappendiculate, tegmic-endotestal seeds, with secondarily thickened endotesta and undulate or costate tegmen, are common characteristics of the tankless lineages. Long oblongoid-obovoid, appendaged or exappendiculate, exclusively tegmic and mucilaginous seeds are common to core Bromelioideae. Anatomical features of the exotegmen and testa and the number of parenchyma layers in the raphe were more variable and especially useful in delimiting genera and some species. The ontogenetic analysis was essential to propose the primary morphological homology hypotheses for the seed coat characters. Seed coat morphoanatomical features offer a promising source of phylogenetically informative characters for integrative and character evolution approaches for Bromelioideae and possibly other subfamilies of Bromeliaceae.