Stem Anatomy, Phyllotaxy, and Stem Protoxylem Tracheids in Several Species of Ophioglossum. I. O. petiolatum and O. crotalophoroides

Abstract

Phyllotaxy, protoxylem tracheids, and the form of the stem xylem are compared in Ophioglossum petiolatum and O. crotalophoroides. Ophioglossum petiolatum has 2/5 phyllotaxy, a one-trace unilacunar nodal anatomy, leaf traces that are appended along a radius to the stele, and protoxylem that contains tracheids with circular-bordered pits. Ophioglossum crotalophoroides has 1/2 phyllotaxy, a two-trace unilacunar nodal anatomy, leaf traces that are appended along a tangent to the inner surface of the stele, and protoxylem tracheids that include elements with circular-bordered pits. In O. crotalophoroides, the stem develops upside down from a deeply bowl-shaped apex; stem vasculature is distinct from that of the leaf traces and cannot be called a leaf-trace complex. It is difficult to assign specific gaps to specific leaves. There may be no leaf-associated gaps, in the classical sense. Section Euophioglossum is not a natural taxon since it includes species with both single and double leaf traces.