Aspects of Permian palaeobotany and palynology. X. The West- and Central European species of the genus Autunia Krasser emend. Kerp (Peltaspermaceae) and the form-genus Rhachiphyllum Kerp (Callipterid Foliage)

Abstract

A discussion of the West- and Central European species of the natural genus Autunia Krasser emend. Kerp and the form-genus Rhachiphyllum Kerp is presented. These genera include a number of species formerly included in the form-genus Callipteris Brongniart non Bory. The material investigated mainly originates from the Rotliegend (?Upper Carboniferous-Lower Permian) of the Saar-Nahe Basin (F.R.G.). Some of the localities have yielded abundant, apparently more or less autochthonously deposited material. In addition specimens from France, the German Democratic Republic, Poland and Czechoslovakia have been studied. Within the natural genus Autunia, attributable to the family Peltaspermacea Thomas, two species are recognized: Autunia conferta (Sternberg) Kerp and A. naumannii (Gutbier) Kerp. Foliage and reproductive structures are described and discussed. With regard to a natural classification special attention is given to the organization of the ovuliferous organs. The genus is characterized by bilaterally symmetrical megasporophylls with abaxially attached ovules. The polliniferous organs consist of small elongate sporangia attached to peltate megasporophylls. The foliage of Autunia consists of bipinnate to tripinnate fronds with alethopteroid pinnules and equally shaped intercalary pinnules. Autunia is thus far the oldest known peltasperm. The form-genus Rhachiphyllum is characterized by its bipinnate to tripinnate fronds with entire-margined to pinnately lobed alethopteroid normal and rachial pinnules. Six species have been assigned to Rhachiphyllum, viz. R. curretiensis (Zeiller) Kerp, R. diabolica (Zeiller) Kerp, R. lyratifolia (Göppert) Kerp, R. schenkii (Heyer) Kerp and R. subauriculata (Weiss) Kerp. The foliage of Autunia conferta and some species of Rhachiphyllum, e.g., R. schenkii (Heyer) Kerp appears to be very variable. The intraspecific variability of these species could be determined. Variations in foliar morphology partly depend on the stage of development of the plant and the frond. Also ecological factors may have influenced the development of the frond. In the literature there exists a considerable confusion about the specific delimitation of the species treated. A number of the callipterid species previously introduced in the palaeobotanical literature appear to be synonymous with the here accepted and described taxa. The traditional concept of the importance of callipterids in chronostratigraphy and biostratigraphy cannot be maintained. The group has a potential in ecostratigraphical considerations.