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CSPG Special Publications

Abstract


Intl. Symposium of the Devonian system: Papers, Volume II, 1967
Pages 721-730
Biostratigraphy

The stratigraphic occurrence of early land plants and its bearing on their origin

Harlan P. Banks

Abstract

All structures that have been reported to be Silurian or Lower Devonian land plants should be subjected to close scrutiny. Many will be found to lack evidence of those characteristics which are common to land plants; e.g., cuticle, stomates, vascular tissue. Only specimens that are unequivocally land plants should be included in hypotheses as to the time of, or mode of, origin of land-plants. The horizons from which these structures originate must be treated similarly, in the light of the best possible stratigraphic data. The results of such analyses demonstrate that at present, in the Ludlovian Series of the Silurian Period, only one or possibly two genera of land plants, Cooksonia and ?Taeniocrada can be accepted as valid. Both have been reported from Bohemia by Obrhel. In the Gedinnian Series of the Lower Devonian Cooksonia and Zosterophyllum occur in Wales. Thus it is not until the Siegenian Stage of the Coblenzian Series that one begins to find a larger number of genera of land plants, including Protolepidodendron, Taeniocrada, Zosterophyllum, Drepanophycus, Gosslingia, Psilophyton of the ornatum type (non Dawson, new generic name needed), Dawsonites, Baragwanathia, Hedeia, Yarravia. The last three may prove to be Late Gedinnian when further studies of the graptolites associated with them in Australia are complete. In the Emsian Stage of the Coblenzian Series many of the same genera, plus some new ones such as Trimerophyton and Eogaspesiea are found It is of special significance that palynological studies, e.g. Richardson, Chaloner, and others, parallel the findings based on macrofossils. The palynological studies may carry land plants a little further back into the Silurian, and may indicate the occurrence of a few more taxa than are listed above, but they support the concept of a gradual increase in the number of taxa of land plants in Silurian - early Devonian time. This report suggests the following: a) stratigraphic occurrence of early land plants should be reported more precisely, b) the plants reported should be established more carefully as truly land plants, c) it is unnecessary to hypothesize a Cambrian origin for vascular plants.


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