New perspectives on Cooksonia from the Lower Devonian of the Welsh Borderland

New collections of coalified mesofossils of Cooksonia have been made from a Lochkovian (Lower Devonian) locality in Shropshire, England. They allow detailed description of sporangial anatomy in Cooksonia pertoni ssp. apiculispora with inferences for spore dispersal involving disintegration of the distal sporangial wall and maintenance of a rigid rim. Trilete spores, Aneurospora sp. and Streelispora newportensis have been recovered from the same sporangium. A new subspecies Cooksonia pertoni subsp reticulispora contains miospores with laevigate proximal surface bearing a simple triradiate apertural fold, equatorial crassitude and a coarse reticulum of muri on a slightly thickened distal wall. Spores are tentatively assigned to Synorisporites sp.. Cooksonia banksii sp. nov. is based on terminal sporangia in which the spore-containing area is enclosed within the expanded apex of the subtending axis. The cavity is lined by a smooth resilient acellular layer. Well-defined cells are apparent only in the pronounced sporangial rim. Spores are assigned to Ambitisporites avitus, a taxon of particular significance, because it is recorded in the Upper Ordovician and Lower Silurian assemblages which contain the earliest trilete monads. However, it is concluded that spores of such simple morphology may have been produced by a variety of taxa and that ultrastructural studies are necessary to confirm this possibility. These new specimens thus allow further insights into the disparity (via anatomy and in situ spores) of very simple plants and, in providing information on cell construction and arrangement, allow for functional interpretations, particularly relating to spore dispersal. (C) 2002 The Linnean Society of London.