In these plants, when immature leaves pop out of the ground or out of a bud, they are in an erect orientation, and simply expand to full size. As the frond matures, it unrolls and expands to full size.
Roots are adventitious.
Thus, in order to grow to tree-size, these ferns have to have a different method of providing mechanical support for the trunk and those large heavy often tripinnately or more compound leaves. Leptosporangia are interpreted to be more advanced than eusporangia, and heterospory is interpreted to be more advanced than homospory. The exosporic gametophytes of the homosporous ferns are typically epiterrestrial, green, photosynthetic, potentially hermaphroditic, and live independent of the sporophyte. Dr. Robert G. Hamilton in this department has done research on gametophyte growth in ferns. The Cladoxylales is an extinct order of primitivePaleozoic ferns known from Early Devonian to Early Carboniferous age strata.