Seed morphology, anatomy and histochemistry in two Mexican species of Mimosa (Leguminosae, mimosoid clade)

ABSTRACT Mimosa species have biological and ecological importance, they exhibit advantages that make them competitive candidates for ecological restoration; considering that the seed is essential for the establishment of the species, it is required to characterize the seeds morphologically and anatomically, especially those that come from multipurpose plants like the mimosas are. The objective was to study the morphology, anatomy and histochemistry of the seeds of Mimosa aculeaticarpa and M. luisana, with the aim of better contextualising and understanding their ecological implications of the fact that the seed is the fundamental stage for the propagation and perpetuation of the species. The morpho-anatomic study was performed by light microscopy (LM) and scanning electron microscopy (SEM), histochemistry was used for detection of cuticle, lignified cell walls and starches. The seeds of M. aculeaticarpa are ovoid and those of M. luisana are spheroid to ellipsoid. In both species the seed coat shows fracture lines, in M. aculeaticarpa var. aculeaticarpa they are limited to the pleurogram, lens, hilum and micropyle regions, while in M. luisana they occupy the entire surface of the seed. Seed coat surface in M. aculeaticarpa var. aculeaticarpa is simple reticulate and each space that is enclosed by the reticulation is densely rugose, while in M. luisana it only has an irregularly rugose pattern. The micropyle is ellipsoid and protruding (M. aculeaticarpa) or punctiform and sunken (M. luisana). Anatomically, there is a cuticle; the seed coat of M. aculeaticarpa has only macrosclereids, while that of M. luisana also has a layer of osteosclereids. The anatomical characters make it possible to distinguish between the two species. The morpho-anatomical characters prevent initial germination, increase the longevity of the seeds and are the probable cause of impermeability.