Sphenophytes

Segmented plants

The stems and fronds of sphenophytes are made up of successive segments bearing small, rudimentary leaves. Sphenophytes appeared in the Upper Devonian (around 355 Ma) and became abundant throughout the entire Palaeozoic, reaching a peak of diversity in the Carboniferous. Their rhizome, a horizontal underground stem, was an advantage for rapid colonisation of the land, particularly in humid environments.

The growth of these plants is not dichotomous; a principal axis, made up of a succession of nodes and internodes, bears lateral branches which are also made up of the same succession. The plant reproduces by means of spores, which are produced by sporangia grouped together in cones (strobili) situated at the tips of fertile branches.

Sphenophytes, of which horsetails are the sole surviving representatives, are a sister group to ferns.