PROGRESS AND PROSPECTS IN RECONSTRUCTING PLANT PHYLOGENY

Phylogeny reconstruction has become respectable science over the last few decades, and trees are accumulating rapidly in the literature. Botanists have been active in this effort and can already cite success stories (e.g., recognition of streptophytes, stomatophytes, anthophytes, eudicots). Nevertheless, only a small number of problems have been addressed and some of these have resisted solution. To solve the toughest problems, especially those involving ancient, rapid radiations, various sources of data will need to be combined, including evidence from fossils. Furthermore, in view of limitations in analyzing data sets with many taxa, more attention must be paid to the consequences of different taxon sampling strategies and to how large, variable taxa can be represented in more inclusive studies. Over the next few years we should continue to move toward a phylogenetic system (monophyletic groups defined by ancestry, diagnosed by characters), which will entail the elimination of familiar paraphyletic taxa. We can expect increased use of phylogenies by ecologists, molecular biologists, and others, which will force us to attend to the issue of the reliability of phylogenetic hypotheses, and will necessitate the development of a database of phylogenetic studies. Interactions with population biologists promise to be especially productive, since there are obvious mutual concerns centered on the analysis of gene trees and reticulation.