Embryology and relationships of Lauraceae (Laurales)

Abstract

Embryology of Lauraceae, hitherto poorly known, was investigated on the basis of 35 species from 23 genera to contribute to a better understanding of familial and generic relationships. Data from the genera investigated and from the literature show that the genera of Lauraceae are 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 common with Hernandiaceae. However, since several core lauralean families such as Amborellaceae, Monimiaceae, and Gomortegaceae are little known embryologically, these must be studied for critical comparison. Within Lauraceae, Cassytha is clearly distinct from the rest of the family in having an ab initio cellular type endosperm (a plesiomorphy, also reported in Umbellularia) instead of a nuclear type endosperm (an apomorphy) 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 subfamily. 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 embryo sac protruding from the nucellus (an apomorphy) distinguishes five genera (Beilschmiedia, Caryodaphnopsis, Cryptocarya, Endiandra, Potameia) and one species of Ocotea (O. rubra) from the rest of the family. These results can properly be incorporated in a future suprageneric classification. The distinctness of Ocotea rubra within the genus is also discussed. (C) 1998 The Linnean Society of London