Abstract
Great advances have been made in our understanding of the phylogeny and classification of Agavaceae in the last 20 years. In older systems Agavaceae were paraphyletic due to overemphasis of ovary position or habit. Discovery of a unique bimodal karyotype in Agave and Yucca eventually led to a reexamination of concepts and relationships in all the lilioid monocots, which continues to the present day. Developments in cytogenetics, microscopy, phylogenetic systematics, and most recently DNA technology have led to remarkable new insights. Large-scale rbcL sequence studies placed Agavaceae with the core Asparagales and identified closely related taxa. Analysis of cpDNA restriction sites, rbcL, and ITS nrDNA sequences all supported removal of Dracaenaceae, Nolinaceae, and clarified relationships. Agavaceae s.s. presently consists of Agave, Beschorneria, Furcraea, Hesperaloe, Hesperoyucca, Manfreda, Polianthes, Prochnyanthes, and Yucca. In this paper we analyze recently obtained ndhF sequence data from Agavaceae and Asparagales and discuss the implications for classification. Parsimony analysis of ndhF data alone resolves most genera of Agavaceae and supports the inclusion of Camassia, Chlorogalum, Hesperocallis, and Hosta within Agavaceae s.l. Analysis of combined ndhF and rbcL data sets of selected Asparagales results in better resolution and stronger bootstrap support for many relationships. Combination of all available ndhF, rbcL, and ITS data in a single analysis results in the best resolution currently available for Agavaceae s.l. Implications for classification schemes past and present are discussed.
Highlights
Agavaceae are a family of rosette-forming, often spiny plants centered in warm and dry areas of Mexico, the southwestern USA, and Caribbean basin
In this paper we review some of the major ideas in Agavaceae classification and report the results of phylogenetic studies utilizing recently acquired chloroplast ndhF sequences, alone and in combination with previously published rbcL and nuclear ITS rDNA data sets
We focused on the relationships of Agavaceae within Asparagales using combined ndhF and rbcL data sets with a larger number of taxa representing major clades of Asparagales
Summary
Agavaceae are a family of rosette-forming, often spiny plants centered in warm and dry areas of Mexico, the southwestern USA, and Caribbean basin. The family includes plants of great natural beauty, ornamental value, cultural significance, and economic importance. The family is recognized there have been questions about the circumscription of Agavaceae, how the genera are related to each other, and how Agavaceae are related to other families. The undisputed genera of Agavaceae s.s. are Agave L., Beschorneria Kunth, Furcraea Vent., Hesperaloe Engelm., Hesperoyucca (Engelm.) Baker, Manfreda Salisb., Polianthes L., Prochnyanthes S. Associated genera such as Camassia Lind!., Chlorogalum (Lind!.) Kunth, Hesperocallis A. Have certain similarities to Agavaceae and have been considered closely related by some, but have never been fully integrated into the family Hosta Tratt. have certain similarities to Agavaceae and have been considered closely related by some, but have never been fully integrated into the family
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