Comparative anatomy and systematics of the orchid tribe Vanilleae excluding Vanilla

Abstract

Vanilleae have been divided into three subtribes consisting of ten genera. We had material for study of all except Dictyophyllaria in subtribe Vanillinae. All genera except Vanilla have few species Clematepistephium and Dictyophyllaria are monospecific. Leafy types have adaxial and abaxial stomata except Clematepistephium , Epistephium, and Eriaxis which have only abaxial tetracytic and anomocytic stomatal apparatuses. Cyrtosia, Erythrorchis, Galeola, and Lecanorchis are leafless. Hypodermis occurs in leaves of Pseudovanilla, Clematepistephium, and Eriaxis; leaves of Epistephium lack a hypodermis. Mesophyll is homogeneous. Stems of Cyrtosia, Galeola, and Eriaxis and rhizomes of Cyrtosia have a hypodermis. A uniseriate velamen occurs in roots of Erythrorchis, Pseudovanilla, Clematepistephium , and Lecanorchis; roots of other genera are bounded by a simple epidermis. Exodermal cell walls are -thickened; endodermal cell walls are ○-thickened. Vascular tissue of roots is variously embedded in sclerenchyma or parenchyma; similarly, pith may be sclerenchymatous or parenchymatous. Cladistic analyses result in two equally parsimonious trees with Epistephium and Eriaxis reversed in placement in each tree. Both trees constitute a paraphyletic complex giving rise to a clade containing the monophyletic Lecanorchidinae and Galeolinae. Vegetative anatomical characters have some phylogenetic value in Vanilleae, but they are not useful in resolving placement of the large and polymorphic genus Vanilla .