Two kinds of isoetalean lycopsids widely prevailed in the Triassic, the Pleuromeia-type and the Annalepis-type, the latter including a plexus of closely related genera. Comparative studies using new macromorphological and ultrastructural data suggest that both genera are interconnected and closely related to Isoetes. Morever they suggest that Annalepis is probably ancestral to Isoetes, via Isoetites. Besides several of the morphological and ultrastructural features of the Triassic lycopsids and Isoetes also appear to be present in some of the most ancient lycopsids, suggesting that the lineage including the modern Isoetales has a very remote origin.
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Grauvogel‐Stamm et al. (2001) studied this question.
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