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Structure of corystospermaceous ovules from the Upper Triassic of Zimbabwe

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Abstract:

Isolated ovules from the Upper Triassic of Zimbabwe were observed using three complementary approaches: light microscopy and, for the first time, scanning electron microscopy and transmission electron microscopy. Complete ovules showed a curved bifid micropylar tube. Three envelopes were present: integument, nucellus, and megaspore. The integument appeared resiniferous. The nucellus was made up of bulging cells around the pollen chamber, which contained bisaccate pollen grains. The ultrastructure of the nucellus revealed a lamellar organization in their microsinuosities. The megaspore membrane was made up of agglomerate rounded bodies more or less closely arranged and surrounded by two layers. The material may be attributed to Umkomasiaceae. A comparison with ovules of different related groups (seed ferns, Caytoniales, Ginkgoales, Nilssoniales, and Coniferales) was made. The Umkomasiales are considered to be a more primitive group than the Pteridospermales with regard to integument and nucellus.

Des ovules isolés du Trias terminal de Zimbabwe ont été observés avec trois approches complémentaires, au microscope photonique et pour la première fois au microscope électronique à balayage et à transmission. Les ovules complets montrent un tube micropylaire bifide recourbé. Trois enveloppes ont pu être étudiées : un tégument, un nucelle et une mégaspore. Le tégument semble résinifère. Le nucelle est constitué de cellules bombées autour de la chambre pollinique qui contient des grains de pollen à ballonnets. L’ultrastructure du nucelle révèle une organisation lamellaire dans les microsinuosités. La membrane de la mégaspore est constituée de corps arrondis plus ou moins agglomérés, limitée par deux couches. Le matériel a pu être attribué aux Umkomasiaceae. Une comparaison avec l’organisation des ovules de différents groupes apparentés (fougères à ovules, Caytoniales, Ginkgoales, Nilssoniales et Coniférales) est faite. Les Umkomasiales sont considérés comme représentant un groupe plus primitif que celui des Ptéridospermales sur la base du rapport tégument/nucelle.

Document Type: Research Article

Publication date: September 1, 2009

More about this publication?
  • Published since 1929, this monthly journal features comprehensive research articles and notes in all segments of plant sciences, including cell and molecular biology, ecology, mycology and plant-microbe interactions, phycology, physiology and biochemistry, structure and development, genetics, systematics, and phytogeography. It also publishes commentary and review articles on topics of current interest, contributed by internationally recognized scientists.

    Previously published as the Canadian Journal of Botany
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