Seed plant phylogeny is evaluated using a data set of 46 terminals (taxa) and 103 morphological and anatomical characters. Cladistic analyses using the criterion of parsimony were performed on the complete data set as well as on subsets of the data, e.g., excluding fossils and/or combining various complex taxa into single terminals. The results support the placement of the cycads as the sister group of a monophyletic group that includes several fossil "seed ferns" as well as extant Ginkgo, conifers, gnetopsids, and angiosperms. When fossils were included, Bennettitales (cycadeoids) were part of an "anthophyte" clade that included gnetopsids and angiosperms. Pentoxylon was a sister taxon to the core anthophyte clade, in some, but not all, of the most parsimonious trees. Caytonia was not found to be closely associated with the anthophyte clade, but instead was often associated as a sister taxon of the glossoptends, and these two taxa were consistently outside of the Gin&go-conifer-anthophyte clade. In all most parsimonious trees for all analyses, Ephedra was to the outside of a clade that included all angiosperm taxa, Gnetum, and Welwitscnia, thus rendering the traditional gnetopsid clade paraphyletic. New information is provided on the morphology of Caytonia and some previous interpretations of homology of the caytonian "cupule" are rejected. The effects of sampling, compartmentalization, and polymorphism are explored in these data, snowing how different results may be obtained when polymorphic or "summary" terminals are used. The need for more work on gnetopsids and fossil taxa is suggested.

The rapid diversification and ecological dominance of the flowering plants beg the question "Why are there so many angiosperm species and why are they so successful?" A number of equally plausible hypotheses have been advanced in response to this question, among which the most widely accepted highlights the mutually beneficial animal-plant relationships that are nowhere better developed nor more widespread than among angiosperm species and their biotic vectors for pollination and dispersal. Nevertheless, consensus acknowledges that there are many other attributes unique to or characteristic of the flowering plants. In addition, the remarkable coevolution of the angiosperms and pollination/dispersal animal agents could be an effect of the intrinsic adaptability of the flowering plants rather than a primary cause of their success, suggesting that the search for underlying causes should focus on an exploration of the genetic and epigenetic mechanisms that might facilitate adaptive evolution and speciation. Here, we explore angiosperm diversity promoting attributes in their general form and draw particular attention to those that, either individually or collectively, have been shown empirically to favor high speciation rates, low extinction rates, or broad ecological tolerances. Among these are the annual growth form, homeotic gene effects, asexual/sexual reproduction, a propensity for hybrid polyploidy, and apparent "resistance" to extinction. Our survey of the literature suggests that no single vegetative, reproductive, or ecological feature taken in isolation can account for the evolutionary success of the angiosperms. Rather, we believe that the answer to Darwin's second "abominable mystery" lies in a confluence of features that collectively make the angiosperms unique among the land plants.

The fossil record has played an important role in the history of evolutionary thought, has aided the determination of key relationships through mosaics, and has allowed an assessment of a number of ecological hypotheses. Nonetheless, expectations that it might accurately and precisely mirror the progression of taxa through time seem optimistic in light of the many factors potentially interfering with uniform preservation. In view of these limitations, attempts to use the fossil record to corroborate phylogenetic hypotheses based on extensive comparisons among extant taxa may be misplaced. Instead we suggest a method-minimum age node mapping-for combining reliable fossil evidence with hypotheses of phylogeny. We use this methodology in conjunction with a phylogeny for angiosperms to assess timing in the history of major angiosperm clades. This method places many clades both with and without fossil records in temporal perspective, reveals discrepancies among clades in propensities for preservation, and raises some interesting questions about angiosperm evolution. By providing a context for understanding the gaps in the angiosperm fossil record this technique lends credibility and support to the remainder of the angiosperm record and to its applications in understanding a variety of aspects of angiosperm history. In effect, this methodology empowers the fossil record.

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