Paleodicots
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Paleodicots (sometimes spelled "palaeodicots") is an informal name used by botanists (Spichiger & Savolainen 1997, Leitch et al. 1998) to refer to a group of flowering plants traditionally considered dicotyledons but excluded from the monophyletic group eudicots in classifications based on molecular systematics.
Molecular phylogenies have shown that within the flowering plants (angiosperms), there are two major clades, recognized in the APG II system as the monocots and the eudicots (tricolpates in some references). Both are monophyletic groups. The majority of plants traditionally recognized as "dicots" fall within the eudicot clade, but there is a non-monophyletic residue of early-diverging groups included in the dicots in older systems (e.g., the Cronquist system). These early-diverging dicots have been dubbed the "paleodicots" and correspond to Magnoliidae sensu Cronquist 1981 (minus Ranunculales and Papaverales) and to Magnoliidae sensu Takhtajan 1980 (Spichiger & Savolainen 1997). Some of the paleodicots share apparently plesiomorphic characters with monocots, e.g., scattered vascular bundles, trimerous flowers, and non-tricolpate pollen.
The "paleodicots" are not a monophyletic group and the term has not been widely adopted. The APG II system does not recognize a group called "paleodicots" but assigns these early-diverging dicots to several orders and unplaced families: Amborellaceae, Nymphaeaceae (including Cabombaceae), Austrobaileyales, Ceratophyllales (not included among the "paleodicots" by Leitch et al. 1998), Chloranthaceae, and the magnoliid clade (orders Canellales, Piperales, Laurales, and Magnoliales). Subsequent research has added Hydatellaceae to the paleodicots.
[edit] References
- Leitch, I. J., M. W. Chase, and M. D. Bennett. 1998. Phylogenetic analysis of DNA C-values provides evidence for a small ancestral genome size in flowering plants. Annals of Botany 82 (Suppl. A): 85-94.
- Rudolphe Spichiger & Vincent Savolainen. 1997. Present state of Angiospermae phylogeny. Candollea 52: 435-455 (text).
