Comparative anatomy of selected rhizomatous and tuberous taxa of subfamilies Orchidoideae and Epidendroideae (Orchidaceae) as an aid to identification

Abstract

This article addresses the vegetative anatomy (leaves, stems, roots, root tubers and rhizomes) of 13 species of subfamily Orchidoideae (Orchidaceae), belonging to the genera Neottia Guettard, Cephalanthera L.C.M. Richard, Epipactis Zinn, Limodorum Boehmer, Spiranthes L.C.M. Richard, Platanthera L.C.M. Richard, Serapias L., Himantoglossum W.D. Koch and Anacamptis L.C.M. Richard, because anatomical studies have provided very useful criteria for orchid diagnosis. In the study three types of painting methods—Delafield’s hematoxylin and safranin, Alcian blue-periodic acid schiff, and alcoholic phloroglucinol + HCl—were employed, and identification tables were prepared. Anatomical results demonstrated the differences in the leaf anatomy of tuberous and rhizomatous orchids. In the stem anatomy, all the rhizomatous genera were found to be anatomically different, especially in regard to the collateral vascular bundles, the distribution of vascular bundles and xylem properties. In root anatomy, the central cylinder, pith, endodermis and/or pericycle properties are distinctive features in all studied taxa. For root tubers, velamen layering, wall outline mucilage cell patterns in ground tissue and arrangements of vascular arches can be used to label taxa. Regarding the rhizome anatomy of the studied taxa, vascular cylinder results in particular were very significant for the distinction of genera. Finally, we strongly emphasize the importance of this kind of detailed anatomical study to solve identification problems of orchid taxonomy.