Osmunda (Osmundaceae) from the Triassic of Antarctica: an example of evolutionary stasis

Compressed specimens of the fern Osmunda are described from the Triassic of the Allan Hills, Antarctica. The specimens consist of a once pinnate, deeply pinnatifid fertile frond as well as several sterile specimens. Six pinnae are present on the partial fertile rachis, with two sterile pinnae above...

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Bibliographic Details
Published in:American journal of botany 1998-06, Vol.85 (6), p.888-895
Main Authors: Phipps, C.J, Taylor, T.N, Taylor, E.L, Cuneo, N.R, Boucher, L.D, Yao, X
Format: Article
Language:English
Subjects:
ANATOMIA DE LA PLANTA
ANATOMIE VEGETALE
Antarctic regions
ANTARCTICA
ANTARCTIQUE
ANTARTIDA
BOTANICA
BOTANIQUE
BOTANY
compression
DESCRIPTIONS
DIMENSION
DIMENSIONS
ESPECE NOUVELLE
ESPECIES NUEVAS
EVOLUCION
EVOLUTION
FERNS
FERTILIDAD
FERTILITE
FERTILITY
FEUILLE
Filicales
Flowers & plants
Fossils
FOUGERE
fronds
Genera
HELECHOS
HOJAS
LEAVES
NEW SPECIES
Osmunda
Osmundaceae
PALAEONTOLOGY
Paleobotany
PALEONTOLOGIA
PALEONTOLOGIE
PLANT ANATOMY
Plant morphology
Plants
Prehistoric era
RHIZOME
RHIZOMES
RIZOMAS
SIZE
Sporangia
TAXONOMIA
TAXONOMIE
TAXONOMY
Triassic
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Description
Summary:Compressed specimens of the fern Osmunda are described from the Triassic of the Allan Hills, Antarctica. The specimens consist of a once pinnate, deeply pinnatifid fertile frond as well as several sterile specimens. Six pinnae are present on the partial fertile rachis, with two sterile pinnae above four fertile pinnae. Both sterile and fertile specimens are virtually identical to the modern species Osmunda claytoniana. Entire fronds are fragmentary; the longest is 21 cm in length. Sterile pinnae are alternate and deeply pinnatifid, with slightly toothed pinnules and dichotomous venation. Fertile pinnae are 1-1.3 cm long, once pinnate, and lack vegetative lamina. Sporangia are clustered, each 300-375 micrometers in diameter, and possess a transverse annulus 6-8 cells long; dehiscence is by a vertical slit. Fronds arise from a rhizome 4 cm long by 1 cm wide; two croziers are present on the rhizome. Two frond segments up to 6 cm long and three deeply pinnatifid pinnae are present on the uppermost part of one rachis. Pinnules are approximately 4 mm long and 2-3 mm wide. The presence of this Osmunda species in the Triassic demonstrates stasis of frond morphology, both fertile and vegetative, for the genus
ISSN:0002-9122
1537-2197
DOI:10.2307/2446424