Shuklina A.S., Polevova S.V.
В журнале Paleontological Journal
Год: 2007 Том: 41 Номер: 3 Страницы: 312-318
Although tree ferns dominated the Mesozoic flora, their taxonomic relationships are poorly understood at the generic level, and next to nothing can be said of evolutionary trends within the group. At least five genera are recognized based on the remains of spore-bearing structures. However, the dispersed spores belong to the same generalized morphotype, and cannot be assigned to genera based on macroscopic remains of fertile leaves. Electron microscopy of spores in situ may partly resolve these problems providing additional criteria for classification of spore-bearing structures and disperse spores. We studied in situ spores of the Early Cretaceous Alsophilites nipponensis (Oishi) Krassilov, which are comparable to dispersed spores Cyathidites minor Coup. Spore wall micromorphology and ultrastructure indicate their affinities with the modern genus Alsophila R. Brown. Only occasional poorly preserved striate sculptures survive the standard treatment of maceration of the perispore. Our data confirm the primitive status of the species with a great number of spores per sporangium, thick unsculptured exospore consisting of two ultrastructural layers, and the possibility that whole sporangia with unshed spores can function as dispersal units.
