Angiospermae

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The earliest fossil angiosperm, ''[[Archaefructus]]'', comes from the [[Yixian]] formation in China and is dated to about 125 million years BP (Sun ''et al.'', 2002). Angiosperm pollen has been found in the fossil record perhaps as long ago as 130 million years.
The earliest fossil angiosperm, ''[[Archaefructus]]'', comes from the [[Yixian]] formation in China and is dated to about 125 million years BP (Sun ''et al.'', 2002). Angiosperm pollen has been found in the fossil record perhaps as long ago as 130 million years.
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The relationships of angiosperms to other plant [[taxon|taxa]] remain contentious (see Friedman & Floyd, 2001, for an overview). Morphological data indicated that the [[Gymnospermae|gymnosperms]] were [[paraphyletic]] with regard to the angiosperms, and that the [[Gnetales]] were the closest living relatives of the angiosperms. However, molecular data have indicated that modern gymnosperms form a [[monophyletic]] sister group to angiosperms, with the Gnetales more closely related to (possibly even within) the [[Pinopsida|conifers]]. However, as the gymnosperm [[crown group]] dates back to the [[Carboniferous]], the angiosperm [[stem group|stem]] must have diverged by that time if the molecular analyses are correct. A number of fossil seed plant groups of uncertain relationships are known from within that time frame, and it seems likely that at least some of these taxa lie on the angiosperm stem. Taylor ''et al.'' (2006) demonstrated that [[oleanane]], a [[diagenesis|diagenetic]] product of organic compounds found in angiosperms but absent from living gymnosperms, was present in fossils of the [[Cretaceous]] [[Bennettitales]] and [[Permian]] [[Gigantopteridales]], making these two groups likely angiosperm stem candidates. Other fossil taxa that have been suggested as angiosperm relatives include the [[Glossopteridales]] and ''[[Caytonia]]''.
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The relationships of angiosperms to other plant [[taxon|taxa]] remain contentious (see Friedman & Floyd, 2001, for an overview). Morphological data indicated that the [[Gymnospermae|gymnosperms]] were [[paraphyletic]] with regard to the angiosperms, and that the [[Gnetales]] were the closest living relatives of the angiosperms. However, molecular data have indicated that modern gymnosperms form a [[monophyletic]] sister group to angiosperms, with the Gnetales more closely related to (possibly even within) the [[Pinopsida|conifers]]. However, as the gymnosperm [[crown group]] dates back to the [[Carboniferous]], the angiosperm [[stem group|stem]] must have diverged by that time if the molecular analyses are correct. A number of fossil seed plant groups of uncertain relationships are known from within that time frame, and it seems likely that at least some of these taxa lie on the angiosperm stem. Taylor ''et al.'' (2003) demonstrated that [[oleanane]], a [[diagenesis|diagenetic]] product of organic compounds found in angiosperms but absent from living gymnosperms, was present in fossils of the [[Cretaceous]] [[Bennettitales]] and [[Permian]] [[Gigantopteridales]], making these two groups likely angiosperm stem candidates. Other fossil taxa that have been suggested as angiosperm relatives include the [[Glossopteridales]] and ''[[Caytonia]]''.
Within the angiosperms, recent phylogenetic analyses have mostly agreed that the so-called ANITA grade (including ''[[Amborella]]'', [[Nymphaeales]] and [[Austrobaileyales]]), includes the basalmost living clades. The Austrobaileyales are most likely closer to the remaining angiosperms than are ''Amborella'' and Nymphaeales. Analyses disagree on whether ''Amborella'' alone or an ''Amborella'' + Nymphaeales clade represents the basalmost branch of angiosperms, but the former option is perhaps the more popular. Saarela ''et al.'' (2007) recently demonstrated that the [[Hydatellaceae]] also fall in this area as the sister group to Nymphaeales. The other major angiosperm clades (listed below) form a monophyletic group, but relationships between the clades are uncertain.
Within the angiosperms, recent phylogenetic analyses have mostly agreed that the so-called ANITA grade (including ''[[Amborella]]'', [[Nymphaeales]] and [[Austrobaileyales]]), includes the basalmost living clades. The Austrobaileyales are most likely closer to the remaining angiosperms than are ''Amborella'' and Nymphaeales. Analyses disagree on whether ''Amborella'' alone or an ''Amborella'' + Nymphaeales clade represents the basalmost branch of angiosperms, but the former option is perhaps the more popular. Saarela ''et al.'' (2007) recently demonstrated that the [[Hydatellaceae]] also fall in this area as the sister group to Nymphaeales. The other major angiosperm clades (listed below) form a monophyletic group, but relationships between the clades are uncertain.

Revision as of 03:28, 24 August 2008

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