Anatomy of the seed and seedling of Spartina alterniflora Lois. (Poaceae)

Abstract

Members of the genus Spartina are dominant macrophytes in many salt marshes of North and South America, Europe and Africa. Although the genus is of great ecological importance, seeds and seedlings of its 16 species have not been described. The seed and seedling of an American species, Spartina alterniflora Lois., are described here. The embryo is enclosed in a lemma, a palea and two glumes. Vascularization of the embryo is panicoid. After germination, leaves arise by periclinal division of cells of the first tunica layer. Laminae assume the adult form by the growth of ribs and formation of furrows on the adaxial surface. The panicoid anatomy of each furrow contains a vascular bundle surrounded by a bundle sheath and large nucleated parenchyma (Kranz) cells. Radiating chlorenchyma extends from the Kranz cells to the epidermis. Stomata were found only on the adaxial lamina surface, and hydathodes on the adaxial and abaxial surfaces. Sclerenchyma is not present in the lamina of the seedling leaf, but layers of cells above and below the parenchymatous bundle sheath appear to be precursors of sclerenchyma. The primary seminal root is composed of an epidermis, a cortex composed of an outer layer of thick-walled parenchyma and an inner layer of thin-walled parenchyma, and an endodermis that surrounds metaxylem vessels in a triarch configuration. The anatomy of S. alterniflora is that of a C 4-Kranz plant adapted for living in the estuarine environment. The highly developed mesocotyl of the seed may function in osmoregulation.