The ontogenesis of the stigmas of 31 species from four of the five subfamilies of the Orchidaceae was studied by means of light- scanning- and transmission electron microscopy. The investigated Cypripedioideae show massive stigmas (WN type), all examined Spiranthoideae, Orchidoideae and "Neottieae'' with the exception of Cephalanthera show papillate stigmas (WP type) and the examined Epidendroideae s. str. and Cephalanthera show detached stigmatic cells (WDc type). The stigma of Vanilla is initiated papillate but exhibit so many special ultrastructural features that it is considered a stigma type of its own (Vanilla type). Within all taxa the outer surface of the stigma to the environment is covered by a stigmatic cuticle, originating from a cuticle.
The anatomical ontogeny of all stigma types runs through the subsequent phases of initiation, secretion and decline. The stigmatic cells produce a stigmatic secretion consisting of hydrophilic and hydrophobic components via merocrine and / or eccrine, later on holocrine pathways. The WDc type and the stigmatic cuticle are interpreted as adaptations of the gynoeceum to the transfer of large pollen masses. The rostellum of Neottia develops analogously to that of the remaining orchids.
Common anatomical and ultrastructural features lead to the classification of the orchid stigma as a collenchymatic, schizogenous gland tissue and confirm the monophyly of the family. The WDc type is interpreted as an autapomorphy and a possible new systematic classification of Cephalanthera is discussed.
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