The early land plant Cooksonia bohemica from the Pridoli, late Silurian, Barrandian area, the Czech Republic, Central Europe

Abstract

ABSTRACT Cooksonia bohemica Schweitzer (= Aberlemnia bohemica (Schweitzer) Sakala, Pšenička et Kraft) from Přídolí strata of the Barrandian area in the Czech Republic is revised, and its morphology is documented in detail. The holotype bears sporangia that, although reniform, do not possess a slit that would allow valvate opening as assumed in earlier studies. Its axes do not show consistent shortening of segments towards the distal portion of the plant as is typical for Aberlemnia Gonez et Gerrienne. The axes contain tubular structures interpreted here as cells of conducting tissues. Masses of subtriangular trilete spores with equatorial crassitudo and finely microgranulate sculpture are of the Ambitisporites type. Cooksonia bohemica is compared with all species of Cooksonia Lang described previously. Additionally, comparisons are made with the related genus Aberlemnia. Based on studies of the type material of both taxa, we suggest retaining the species in Cooksonia. Cooksonia bohemica is differentiated from other taxa based on a combination of branching pattern, sporangial shape, and spore morphology. The remains are interpreted to be the sporophyte of an early land plant referable to tracheophytes based on the presence of vascular strands in its axes. A general radiation of cooksonioids away from a core region around the Rheic Ocean is proposed for the Silurian–Devonian transition.