The most interesting point in the structure of the leaf-base is the presence of a ligule, like that of Isoetes or Selaginella, which was seated in a deep pit, opening on the upper surface of the cushion, just above the insertion of the lamina.
A number of species of Lycopodium are epiphytic and those of Isoetes live submerged in water.
Found the most serviceable: - Hydrophytes (submerged aquatic plants) .Plants whose vegetive organs live wholly in water; e.g., most Algae, many mosses, ch as Fontinalis spp., and liverworts, such as Jungermannia spp.; few Pteridophytes, such as Pilularia spp., Isoetes spp.; several wering plants, such as Potamogeton pectinatus, Ceratophyllum p., Hottonia palustris, Utricularia spp., Liltorella lacustris.
The rootlets, which branched by dichotomy, contain a slender monarch stele exactly like that in the roots of Isoetes and some Selaginellae at the present day; they possessed, however, a complex absorptive apparatus, consisting of lateral strands of xylem, connecting the stele with tracheal plates in the outer cortex.