An order in the class Lycopsida that diverged from the Lepidodendrales in the Late Devonian. These two groups have several characters that are not found in other lycopsids, notably a centralized, shootlike rooting structure (rhizomorph) that allows finite growth, wood production, and tree-sized dimensions. Isoetaleans evolved from trees as an increasingly specialized and reduced lineage; all but the earliest are small-bodied shrubs and pseudoherbs. A reduced morphology characterizes the only living isoetalean genus, Isoetes.