Morphology and micromorphology of the seed coats of species of Echinodorus (Alismataceae) from Brazilian Northeastern

The morphology and the micromorphological characteristics of the surface of seeds of ten species of Echinodorus Rich. & Engelm. ex. A. Gray which occurs in northeastern Brazil were examined using scanning electron microscopy. The diversity of the observed ornaments allowed to distinguish the seed testa of the studied species as follows: scalariform in E. pubescens (Martius) Seubert, tenuous ribbed in E. tenellus (Martius) Buchenau, tenuous reticulate in E. reticulatus Haynes & Holm-Nielsen, reticulate channeled in E. grandilforus (Chamisso & Schlechtendal) Micheli subsp. aureus (Fassett) Haynes & Holm-Nielsen, reticulated in E. glandulosus Rataj, reticulated-foveate in E. paniculatus Micheli and E. lanceolatus Rataj, and reticulated tenuous foveate in E. palaefolius (Nees & Martius) MacBride, E. subalatus (Martius) Grisebach and E. macrophyllus (Kunth) Micheli subsp. scaber (Rataj) Haynes & Holm-Nielsen. The complete description presents observations of the form of the component cells of the testa of these seeds, their anticlinal boundaries with respective cell junctions and cell wall thicknesses. The results suggest the importance of the seed micromorphology as a synthetic character to infra-generic classification of Echinodorus.