Floral anatomy, ultrastructure and chemical analysis in Dactylorhiza incarnata/maculata complex (Orchidaceae)

Four Dactylorhiza taxa in the D. incarnata/maculata complex were examined to identify differences in floral traits, using micromorphological, histochemical and ultrastructural studies on spur and labellum structure. Flowers were collected at anthesis from four monospecific populations in Gdańsk, Pomerania, northern Poland. The flowers revealed secretory activity of the epidermis of the spur mouth (possible osmophores) and of the inner epidermis of spurs (possible nectar traces) in D. incarnata, D. maculata subsp. fuchsii and D. majalis subsp. majalis. The secretion was absent on papillae in D. maculata subsp. maculata. However, the presence of slightly developed micro-channels, vesicles in periplasmic space and plastoglobuli in plastids may be responsible for production of a meagre amount of fragrance or nectar. The examined Dactylorhiza taxa were also clearly separated by their scent profiles. The most abundant class of compounds is based on the common structure of 4-hydroxybenzene. The presence of vanillin precursors, such as 4-hydroxybenzaldehyde, which, like vanillin, are widely recognized to be important in attracting potential pollinators, was observed mainly in D. incarnata and D. majalis subsp. majalis. The scent compounds were characteristic for a particular species, which may be important for their floral isolation.