Seed Coat Anatomy and Its Relationship to Seed Dispersal in Subfamily Lecythidoideae of the Lecythidaceae (The Brazil Nut Family)

Abstract

The seed coat anatomy of representative species from all 10 Neotropical genera of Lecythidaceae subfamily Lecythidoideae and from the Paleotropical Barringtonia (Lecythidaceae subfamily Planchonioideae) was studied. The seed coat is mainly composed of the testa, which is developed through moderate or intensive multiplication of the outer integument of the ovule. The tegmen, derived from the inner integument of the ovule, is mostly crushed at seed maturity. Barringtonia and Grias, with fruits as diaspores, have an unspecialized exotesta and a poorly differentiated seed coat. In contrast, species of Lecythidoideae, with seeds as diaspores, possess well-differentiated seed coats with diversified protective mechanisms. Examples include: an expanded and lignified exotesta that serves as a water barrier and protects the embryo; an extensive area of tannin cells that provides a chemical defense against pathogens and predators; a thick and sclerotic mesotesta that protects the embryo; and large fibers surrounding and supporting the vascular bundles. In addition, other modifications of the seed coat are probably adaptations for seed dispersal by different dispersal agents. These include the exotestal hairs of Couroupita guianensis, which possibly protect the embryos as they pass through the digestive tracts of peccaries; an extension of the seed coat into a wing in species of Cariniana and Couratari, which facilitate wind dispersal; the papillate exostestal cells of Allantoma lineata, which probably promote dispersal by water; the well-developed arils of species of Corythophora and Lecyt his, probably sought after by animals, which in turn disperse the seeds; and the sarcotesta of Eschweilera ovalifolia, consumed by fish, which in turn disperse the seeds. We conclude that the highly diversified anatomy and morphology of the seed coat of the Lecythidoideae has evolved from relatively homogeneous ovules in response to pathogens and predators as well as to abiotic and biotic dispersal agents.