Abstract

FIGUEROA, Coyolxauhqui; SALAZAR, Gerardo A.; TERRAZAS, Teresa  and  DAVILA, Patricia. Gynostemium structure and development in Dichromanthus michuacanus (Orchidaceae, Spiranthinae). Rev. Mex. Biodiv. [online]. 2012, vol.83, n.1, pp.73-82. ISSN 2007-8706.

Floral morphology and development of Dichromanthus michuacanus, with an emphasis on the gynostemium, are described and illustrated. Inflorescences at different stages of development were examined by means of scanning electron microscopy and light microscopy. The floral organs differentiate in an adaxial-abaxial direction, in the following sequence: lateral sepals, labellum, petals, anther and dorsal sepal. The carpelar apices appear last between the anther and the labellum. Initially there is elongation of the anther and the median carpel; the latter gives rise to the stigma, rostellum and viscidium, and the lateral carpels do not contribute to the stigmatic receptive surface. The rostellum remnant is narrowly triangular and the viscidium sheaths it almost entirely; at anthesis, a zone of rupture between both structures is evident. The columnar part arises at the end of development. Early organogenesis of D. michuacanus is similar to that of other genera of Spiranthinae studied previously and the structural differences observed originate at the later stages. The structure of the rostellum and viscidium shows a correspondence with the morphology of the pollinator (Bombus diligens, Apidae); the narrow viscidium of D. michuacanus adheres to the dorsal surface of the tongue of the insect.

Keywords : anther; carpels; stigma; gynostemium; ontogeny; pollination; rostellum; viscidium.

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