Several systems of classification have been proposed for the family Ag
avaceae. A distinctive bimodal karyotype and similarities of fruits an
d seeds strongly support close relationships among Yucca, Hesperaloe B
eschorneria, Furcraea, Agave, Manfreda, Polianthes, Prochnyanthes, and
perhaps Hosta. However, Dasylirion, Beaucarnea, Nolina, Calibanus, Dr
acaena, and Sansevieria differ in so many cytological and morphologica
l features that many have concluded they should be excluded from Agava
ceae and separated into two families, Nolinaceae and Dracaenaceae. Chl
oroplast DNA restriction site data support these separations and indic
ate that Nolinaceae and Dracaenaceae are very close to Convallariaceae
(Maianthemum, Convallaria, Aspidistra, Liriope, etc.). In this paper
we report the results of an ITS rDNA sequencing study of 40 taxa in Ag
avaceae sensu late and related groups in the order Asparagales. Sequen
ce alignments were optimized using the Consistency Index, Retention In
dex, and Rescaled Consistency Index to find the alignment that exhibit
ed the least amount of homoplasy. The results of our study are congrue
nt with the conclusions drawn from cytological, immunological, cpDNA,
and rbcL studies, which support a narrow interpretation of Agavaceae a
nd a close relationship among Convallariaceae, Dracaenaceae, and Nolin
aceae. In addition, the ITS sequence data provide evidence for some in
teresting relationships within these families.