Comparative foliar anatomy and systematics of the <i>Trichocentrum</i>-clade with emphasis in <i>Cohniella</i> (Asparagales: Orchidaceae)

Abstract

The genera Cohniella, Lophiarella, Lophiaris, and Trichocentrum are included in the Trichocentrum-clade. These genera are distributed from Florida and Northern Mexico to Southern Brazil and Northern Argentina, growing in tropical deciduous forests or tropical rain forests and thorn scrub forests to pine-oak forest, from sea level to 1 700m. The leaf anatomical structure of 23 members of the Trichocentrum-clade was explored as a source of taxonomic and phylogenetic characters. A total of 11 species of Cohniella, three species of Lophiarella, seven species of Lophiaris, two species of Trichocentrum, and other four species were included as outgroup. Anatomical characters were studied by cross sections and paradermic observations of the middle portion of fresh leaves. Although anatomical characters were fairly homogeneous throughout the clade, twelve vegetative anatomical, phylogenetically informative characters were selected and coded for an analysis that was performed using an exhaustive search (implicit enumeration) implemented through TNT. The strict consensus of 2 692 most parsimonious trees resulted in a poorly resolved polytomy, which however recovers the Trichocentrum-clade with a monophyletic, strongly supported Cohniella nested within it with unifacial leaves and the presence of cellular inclusions in the epidermis as synapomorphies. We concluded that the anatomy characters alone are insufficient to assess the relationships amongst the genera of the Trichocentrum-clade. However, the two synapomorphies recovered for Cohniella strongly support its monophyly when these are analyzed in conjunction with other data sources (e.g., molecular and morphological characters).