ibclogo XVI International Botanical Congess


Abstract Number: 4432
Session = 11.4.3


THE TRIASSIC LYCOSIDS


L. Grauvogel-Stamm* and B. Lugardon^, *EOST-Geologie, University of Strasbourg, France, ^Lab. Biologie Vegetale, Univ. Toulouse, France


Two kinds of lycopsids greatly prevailed in the Triassic: the Pleuromeia-type and the Annalepis-type. Both were considered to belong to the Pleuromeiaceae within the Isoetales. Pleuromeia moroever was long regarded as one of the intermediates between the Carboniferous arborescent lepidodendrids and the living Isoetes. However the isoetaleans were shown to exist long before the lepidodendrids and therefore this ancestor/descendant relationship can no more be accepted. The isoetaleans are part of a complex group of heterosporous lycopsids of which the phylogeny, and particularly the relationships with the lepidodendrids, are unknown. A comparative study of the lycopsid rooting organs underscores the similarities between Pleuromeia and the living Isoetes. The comparative ultrastructure of the spores, both micro- and megaspores, also argues for close relationships between the two genera. The fine structure of the microspores of Annalepis also proves that this genus belongs to the same lineage.


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