Orestovia and the origin of vascular plants

Abstract

The enigmatic Orestovia from the Lower Devonian of Siberia has a vascular cylinder of spiral and annular tracheids, external and internal cuticles in the cortex, and stomata. Abundant spores are occasionally preserved between the cortex cuticles. The ‘reticulate structures’ are thyriothecia of a hemisphaeriacean fungus. Spores of several types are found sticking to the cuticle. Orestovia can be conceived as a transitional form between the alga‐like Protosalvinia and the sporangiate vascular plants. The origin of land plants is discussed.

Systematics and Evolution

“…To some extent, there has been an inherent bias based on the long-held assumption that the group did not evolve until the Cretaceous (Pirozynski and Weresub 1979). Slightly younger (Early Devonian) specimens from Siberia attributed to the Ascomycota include asci and structures interpreted as paraphyses that are regarded as evidence of the Microthyriales (Krassilov 1981). The most often cited of these consists of chains of up to nine multiseptate spores as well as conidiogenous cells (phialides) (Fig.…”

Ascomycete Systematics

“…Krassilov (1981) interprets these structures as thyriothecia that contain angular hypothecial cells, some with prominent hooked hyphae (Fig. 6).…”

“…Present are asci (Fig. 7) and elongate cells that may represent paraphyses (Krassilov, 1981). Some cuticle preparations reveal structures that Krassilov interprets as hyphopodia.…”

“…. Hooked hypha (arrow) in thyriothecium of Orestovia (Devonian; from Krassilov, 1981). Bar scale = 20 j!m.…”

Les Cheirolépidiacées du Jurassique inférieur de Saint-Fromond, bassin de Carentan (Manche—France)

“…12) il n'y a pas de repli visible sur la face adaxiale des écailles. Une deuxième remarque qui va dans le même sens peut être déduite des travaux de Krassilov ( 1982) sur les écailles ovulifères du genre Hirmeriella du Jurassique inférieur de Pologne. Cet auteur souligne une disposition ovulaire comparable à celle observée de nos jours chez les Araucariacees.…”