Morphological Evolution of Stratiotes through the Paleogene in England: An Example of Microevolution in Flowering Plants

Six populations of seeds of the aquatic monocotyledon Stratiotes (Hydrocharitaceae) from the Paleogene of England have been studied to assess morphological evolution through the Eocene–Oligocene transition. Morphometric methodologies (including eigenshape analysis) have been used to quantify evoluti...

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Bibliographic Details
Published in:Palaios 2006-06, Vol.21 (3), p.272-288
Main Authors: SILLE, NICHOLAS P, COLLINSON, MARGARET E, KUCERA, MICHAL, HOOKER, JERRY J
Format: Article
Language:English
Subjects:
Angiospermae
Belchatow Poland
biologic evolution
Biological taxonomies
biometry
Bohemian Basin
Bouldnor Cliff
Cenozoic
Central Europe
Characeae
Czech Republic
England
Europe
Evolution
Felpham England
Fossils
Geology
Great Britain
Gurnard England
Hampshire England
Hordle Cliff
Hydrocharitaceae
Isle of Wight England
Keels
Monocotyledoneae
morphology
Paleobotany
Paleoclimatology
Paleogene
Paleogene period
Plantae
Plants
Poland
principal components analysis
Research Report
RESEARCH REPORTS
seeds
SEM data
Specimens
Spermatophyta
statistical analysis
Stratiotes
Sussex England
Tertiary
Thorness Bay
United Kingdom
Western Europe
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Summary:Six populations of seeds of the aquatic monocotyledon Stratiotes (Hydrocharitaceae) from the Paleogene of England have been studied to assess morphological evolution through the Eocene–Oligocene transition. Morphometric methodologies (including eigenshape analysis) have been used to quantify evolution within the genus and compare results to previous qualitative studies. Previously hypothesized broad evolutionary trends of increasing size and more elongate shape are found to be mainly correct, but, in places, can be elucidated further. The results of this study indicate a single evolving lineage in the Paleogene of southern England with an increase in seed size and keel width in late Eocene specimens, followed by a reversal of this trend in the early Oligocene. Two Miocene populations from continental Europe are shown to be morphologically distinct from those of the English Paleogene. Changes in overall shape of the seed are shown to be controlled dominantly by the relative size of the keel structure, rather than the seed body. Comparisons show that the microevolutionary trend of Stratiotes across the Eocene–Oligocene transition differs from that of the charophyte, Harrisichara. This may suggest that factors other than climatic change, such as animal/plant interactions, played a role in evolution of Stratiotes seeds. Type and figured material of named Paleogene species was added passively to the dataset, and results suggest that taxonomic splitting may have led to previous evolutionary hypotheses of multiple clades, which is not supported by this study.
ISSN:0883-1351
1938-5323
DOI:10.2110/palo.2005.P05-21e