Carvalho et al. 2024 (Article) seeds

The Seed Coat Structure in Bromeliaceae Juss. (Poales): Morphoanatomical Diversity and Insights Into Character Evolution

Author(s):—J.D.T. de Carvalho, I.M. Ramírez-Morillo, E.M.C. Leme & J.E.A. Mariath

Publication:—The Botanical Review : 1-55 (online). (2024) — DOI

Abstract:—The seed coat plays a fundamental role in embryo protection and dispersal, featuring several structural adaptations for these functions in Bromeliaceae. While seed coat characters have been used for taxonomic inferences in Bromelioideae, the only subfamily with zoochoric seeds, the diversity of these traits in the predominantly anemochoric subfamilies remains underexplored. This study aims to elucidate the evolution of structural traits of Bromeliaceae seeds, focusing on the seed coat morphoanatomy within a comprehensive phylogenetic framework. We analyzed 100 species from 52 genera, representing all eight accepted subfamilies of Bromeliaceae, including unpublished data from 60 species in 24 genera and previously published data from Bromelioideae. Standard light microscopy and microtechnique methods were adapted for seed analysis. Ancestral traits were reconstructed using parsimony analysis on a consensus supertree combining previous phylogenies. We identified 53 informative morphoanatomical characters. Key morphological traits include seed shape as well as the presence of chalazal and micropylar appendages. Our findings indicate that elongated, biappendiculate, and terete seeds are plesiomorphic in Bromeliaceae, with the loss of appendages occurring independently multiple times. Testal-exotegmic seeds with sclerified testa are plesiomorphic, evolving into the tegmic-exotestal or tegmic-endotestal state (with collapsed testa in different regions), and becoming strictly tegmic independently in Navioideae and core Bromelioideae. Ancestral character optimization has provided new insights into seed evolution within the family, highlighting that elongate, biappendiculate, and testal-exotegmic seeds are plesiomorphic. Additionally, the newly examined characters offer valuable and unprecedented data for systematics and enhance our understanding of seed dispersal mechanisms in Bromeliaceae.

Keywords:—Anemochory · Character evolution · Dyckia · Monocots · Tillandsia · Seed anatomy