Gymnosperms

Pro-Gymnosperms
Some palaeozoic era fossils from the Devonian and Carboniferous periods were previously assumed to belong to Pteridophytes, but are now thought to be closer to gymnosperms, but not fully gymnosperms. Beck in 1960 identified linkages between two such fossils, archaeopteris fern-like fronds and callixylon gymnosperm-like trunks, these members were classed as the progymnospermopsida, a class of gymnosperms. Progymnosperms are thought to be the origin of both Cycadales and Coniferales by some Palaeobotanists. After the discovery of Rhynie flora and Pteridosperms, Stewart views the discovery of progymnospermopsida to be a watershed event that has improved our understanding of vascular plant evolution more than any other.