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Abstract Detail

Paleobotanical Section


Phylogenetic analyses of Early Cretaceous fossils related to Chloranthaceae and their evolutionary implications.

Since Couper compared Barremian monosulcate pollen called Clavatipollenites with the modern genus Ascarina, Chloranthaceae have been one of the living taxa most often mentioned in discussions of early angiosperms.  By placing Chloranthaceae above the basal ANITA grade, molecular data have refuted suggestions that their unusually simple flowers are primitive, but their position among the remaining angiosperms is uncertain.  We evaluated the phylogenetic position of Early Cretaceous and Cenomanian floral fossils relative to living Chloranthaceae by adding the fossil taxa individually or together to backbone trees in which Chloranthaceae are linked with either magnoliids or Ceratophyllum, the most common alternatives found in molecular and morphological analyses.  Ironically, the one floral type associated with Clavatipollenites pollen, Cenomanian fruits called Couperites containing one anatropous ovule, is ambiguously placed:  it may be a stem relative of Chloranthaceae, a crown group member, or more basal.  Aptian-Albian plants that produced Asteropollis pollen (with a several-branched sulcus), which had male flowers consisting of one stamen and female flowers with one carpel and three adnate tepals, were crown group Chloranthaceae linked with HedyosmumCanrightia (early Albian) was a stem relative of Chloranthaceae (with or without Ceratophyllum) that represents an intermediate stage in floral reduction; it had bisexual flowers with several carpels and stamens but a perianth reduced to one whorl.  Zlatkocarpus (Cenomanian), which had female flowers with a reduced perianth, may be a crown group member sister to Ascarina, Sarcandra, and Chloranthus, or a stem relative of Chloranthaceae plus Ceratophyllum.  Based on our analyses, Aptian-Albian plants that produced coarsely reticulate Pennipollis pollen, which have been assigned to monocots, are instead stem relatives of Chloranthaceae and/or Ceratophyllum.  Despite similarities to Piperales, Appomattoxia (middle Albian), associated with continuous-tectate Tucanopollis pollen, is either near the base of the ANITA grade or related to Chloranthaceae and/or Ceratophyllum.  These results clarify scenarios for floral evolution, indicating that a shift to unisexual flowers with one carpel and one stamen occurred before loss of the perianth and that the bizarre bisexual flowers of Sarcandra and Chloranthus are secondarily derived.  Many uncertainties could be resolved with more evidence on the floral architecture of taxa known only as isolated stamens and carpels.  Association with vegetative organs could address the possibility that some of these fossils are links between a Chloranthaceae-like ancestor and Ceratophyllum.

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1 - University Of California Davis, DEPT OF EVOL & ECOLOGY, One Shields Avenue, Davis, CA, 95616-8537, USA
2 - University of Zurich, Institute of Systematic Botany, Zurich, 8008, Switzerland

fossil flowers

Presentation Type: Oral Paper:Papers for Sections
Session: 21
Location: Whitewater/Grove
Date: Tuesday, July 29th, 2014
Time: 11:15 AM
Number: 21011
Abstract ID:133
Candidate for Awards:None

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