Devonian thalloid plants (Orestoviaceae) and associated spore tetrads

Abstract

Schuguria Tchirkova-Zalesskaya, 1957 is a cutinized mat-forming thalloid plant similar to Orestovia Ergolskaya, 1936, but differs in the crater-like surface structures interpreted as gamentangial conceptacles. Typical stomata is lacking in Schuguria, while the conducting tissue is relatively feebly developed. It is suggested that Schuguria and Orestovia represent sexual and asexual generations of a nearly isomorphic reproductive cycle. Persistent spore tetrads are abundantly preserved in maceration residue of the mats and adhering to cutinized thalloids. On evidence of association and similar ultrastructure of the cuticle and sporoderm, the tetrads might have been produced by a sporophytic member of the Orestoviaceae. At the same time, they are comparable to the Early Palaeozoic tetrads of putative incipient land plants.