A CHLOROPLAST DNA STUDY OF THE AGAVACEAE

A chloroplast DNA restriction site analysis of 40 taxa in the Agavaceae s.l. was undertaken to test the accuracy of several current systems of classification. In Cronquist's system, the Agavaceae contain 18 genera of fibrous-leaved, more or less woody plants such as Yucca, Hesperaloe Agave, Manfreda, Polianthes, Dracaena, Sansevieria, Nolina, Beaucarnea, Dasylirion, and Cordyline. In Dahlgren's system, the Agavaceae are restricted to Yucca, Hesperaloe Agave, Manfreda, Polianthes, Beschorneria, and Furcraea, while the other genera are placed in different families. These contrasting phylogenetic schemes were investigated by a chloroplast DNA restriction site analysis of these genera plus Xanthorrhoea, Hosta, Hypoxis, Hemerocallis, Asparagus, Liriope, Aspidistra, Maianthemum, and Convallaria. Phylogenetic analysis of 110 restriction site mutations, 90 of which were phylogenetically informative, strongly supports the conclusion that there are two major lineages in this group of taxa. One well supported clade contains, sensu Dahlgren, the Nolinaceae, Dracaenaceae, and Convallariaceae. It appears that Nolina and Dasylirion are more closely related to genera such as Liriope, Maianthemum, and Dracaena than to Yucca and Agave. The other major lineage contains Yucca, Hesperaloe Agave, Manfreda, Polianthes, Beschorneria, and Furcraea, with Hosta and perhaps Xanthorrhoea at the base. Asparagus appears to be intermediate between the two lineages. The cpDNA suggests that Cordyline, Hypoxis, and Hemerocallis are not closely related to the Agavaceae.