EMBRYOLOGY AND RELATIONSHIPS OF LAURACEAE (LAURALES)

Embryology of Lauraceae, hitherto poorly known, was investigated on th e basis of 35 species from 23 genera to contribute to a better underst anding of familial and generic relationships. Data from the genera inv estigated and from the literature show that the genera of Lauraceae ar e very similar embryologically, but that differences do exist in a few characters among the genera. Based on comparisons with other families of Laurales, Lauraceae consistently had a pachychalazal ovule or seed with a ramified raphal vascular bundle at chalaza (an apomorphy) in c ommon with Hernandiaceae. However, since several core lauralean famili es such as Amborellaceae, Monimiaceae, and Gomortegaceae are little kn own embryologically, these must be studied for critical comparison. Wi thin Lauraceae, Cassytha is clearly distinct from the rest of the fami ly in having an ab initio cellular type endosperm (a plesiomorphy, als o reported in Umbellularia) instead of a nuclear type endosperm (an ap omorphy) as in the rest of the family, in lacking the nucellar cap and in having the micropyle formed by both the inner and outer integument , facts supporting the traditional taxonomic placement of Cassytha in its own subfamily and the remainder of the family in the other subfami ly. Within the rest of the family, the amoeboid tapetum (an apomorphy) distinguishes 15 genera (Actinodaphne, Cinnamomum, Laurus, etc.) from the six genera with the glandular tapetum. In addition, a mature embr yo sac protruding from the nucellus (an apomorphy) distinguishes five genera (Beilschmiedia, Caryodaphnopsis, Cryptocarya, Endiandra, Potame ia) and one species of Ocotea (O. rubra) from the rest of the family. These results can properly be incorporated in a future suprageneric cl assification. The distinctness of Ocotea rubra within the genus is als o discussed. (C) 1998 The Linnean Society of London.