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Abstract Detail



Themes of land plant evolution, a celebration of the contributions of Leo J. Hickey

Doyle, James [1].

Angiosperm clades in the Potomac Group: what have we learned since Hickey & Doyle 1977?

In their studies on Potomac Group angiosperms, Hickey & Doyle made only broad comparisons of fossils with living taxa, focused on the consistent systematic distributions of pollen and leaf characters at the same horizons. Subsequent discoveries of fossil flowers in the Potomac and coeval deposits by Friis, Crane, Pedersen, and others and increasingly robust molecular phylogenies of living angiosperms allow more precise recognition of extant clades, using a molecular scaffold approach, in which a morphological dataset of living and fossil angiosperms is analyzed with living taxa arranged as in current molecular trees. Hickey & Doyle compared early Potomac (Aptian-early Albian) leaves and monosulcate pollen with “magnoliids” (a paraphyletic group as then defined) and monocots, but flowers provide evidence for particular clades. The basal ANITA grade is represented by Aptian-Albian flowers (Monetianthus, Carpestella) and whole plants (Pluricarpellatia) nested in crown group Nymphaeales; early Potomac reniform leaves could belong to this clade. Epidermal similarities of other early Potomac leaves to woody members of the ANITA grade are consistent with the presence of flowers assignable to Austrobaileyales (Anacostia). Diverse Aptian to Cenomanian mesofossils appear to represent both crown group Chloranthaceae (Asteropollis plant, related to Hedyosmum) and stem relatives of Chloranthaceae and/or Ceratophyllum (Canrightia, Zlatkocarpus, Pennipollis plant, possibly Appomattoxia). Several Albian to early Cenomanian mesofossils belong to Magnoliidae in the new monophyletic sense, including Virginianthus and Mauldinia (Prisca) in Laurales and Archaeanthus in Magnoliales. The reticulate monosulcate pollen of Virginianthus suggests that more dispersed pollen of this type was produced by magnoliids than might be assumed based on living taxa. The presence of monocots, inferred from Aptian Liliacidites pollen and Acaciaephyllum, is confirmed by araceous inflorescences. In the middle-late Albian, the rise of tricolpate pollen and the first locally dominant angiosperm leaves mark the influx of near-basal lines of eudicots, not yet recognized as a clade in 1977. Associated flowers indicate that palmately lobed “platanoids” and Sapindopsis (previously compared with rosids) are both stem relatives of Platanus, while Nelumbites has a similar relationship to Nelumbo, in the same near-basal eudicot order Proteales. Molecular trees suggest that flowers related to Buxaceae (Spanomera) had cordate leaves with teeth, like “Populuspotomacensis.

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1 - University of California Davis, DEPT OF EVOL & ECOLOGY, One Shields Avenue, Davis, CA, 95616-8537, USA

Keywords:
Angiosperms
Cretaceous
phylogeny
mesofossils
Leaves.

Presentation Type: Symposium or Colloquium Presentation
Session: C6
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 5:00 PM
Number: C6014
Abstract ID:764
Candidate for Awards:None


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