THE EMBRYOLOGY AND RELATIONSHIPS OF THE BYBLIDACEAE

The relationships of the Byblidaceae have been the subject of a number of recent molecular phylogenetic studies where their traditional rela tionships with the Roridulaceae and other members of the Rosidae have been overturned in favour of affinities with the Asteridae, in particu lar to the Lentibulariaceae in the Lamiales. Although the embryologica l relationships between these families were the subject of an earlier study, the data for the Byblidaceae were incomplete. The family has te trasporangiate, bilocular anthers with a glandular bi-nucleate tapetum . Formation of the anther wall appears to be of the Dicotyledonous typ e, and the anthers have ephemeral middle layers and apical fibrous thi ckenings. Simultaneous microsporogenesis results in tetrahedral tetrad s of bi-nucleate pollen grains. The ovules are anatropous, unitegmic a nd tenuinucellate. Megasporogenesis is direct from the archesporal cel l, which in Byblis liniflora Salisb. divides to produce a linear tetra d from which a chalazal megaspore is derived (contrary to a report of a micropylar megaspore in B. gigantea Lindl.). Megagametogenesis confo rms to the Polygonum type, and the antipodal cells are persistent. The endosperm is ab initio Cellular and there are well developed micropyl ar and chalazal haustoria. Embryogenesis appears to conform to the Ona grad type noted for several of the other members of the Lamiales s.l., including the Lentibulariaceae, to which the Byblidaceae have been re lated in recent molecular studies.