Embryology of the dioecious Australian endemic Lomandra longifolia (Lomandraceae)

Abstract

Microsporogenesis, embryogeny and endosperm development of Lomandra longifolia Labill. are described in detail. The formation of the anther wall is the basic type composed of four cell layers, namely an epidermis, an endothecium, one middle layer and a tapetum. The tapetum layer has glandular, uninucleate cells. Successive cytokinesis follows meiosis, subsequently forming a tetrahedral tetrad of microspores. The ovule in each carpel is hemitropous, crassinucellate and bitegmic, with the micropyle formed by the inner integument. The archesporial cell divides periclinally to form the primary parietal and primary sporogenous cells. The sporogenous cell functions as the megaspore mother cell, whereas the parietal cell divides to give rise to two parietal layers. The mature megagametophyte, which has enlarged synergids and antipodals, is of the Polygonum type, with the normal complement of seven cells and eight nuclei. Nucellar tissue in the mature ovule consists of enlarged dermal cells and irregular subdermal cells surrounding a central strand of markedly smaller cells. Endosperm development is of the nuclear type. Embryo development is of the Graminad type, characterised by oblique zygotic and early pro-embryonic divisions.