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

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Abstract
Phyllotaxy, protoxylem tracheids and form of the stem xylem were compared in O. petiolatum and O. crotalophoroides. O. petiolatum has 2/5 phyllotaxy, a 1-trace unilacunar nodal anatomy, leaf traces that are appended along a radius to the stele and protoxylem that contains tracheids with circular-bordered pits. O. crotalophoroides has 1/2 phyllotaxy, a 2-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. Sect. Euophioglossum is not a natural taxon since it includes species with both single and double leaf traces.

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