A small extinct order of the class Lycopsida that bridges the evolutionary gap between the primitive Zosterophyllopsida and relatively advanced Lycopsida; hence the asteroxylaleans are often termed prelycopsids. The best-known asteroxylalean species are of Early Devonian age, although similar forms survived to the Late Devonian. All possessed at least some hydrophytic features; together with a paucity of strengthening tissues, this characteristic suggests that they largely relied on hydrostatic pressure for structural support.