Floral structure and gynostemium ultrastructure of two Habenaria species with their taxonomic implications

Abstract

The genus Habenaria exhibits a highly diversity in floral morphology and has complex taxonomy problems. In order to select key taxonomic features of this genus, floral structure and gynostemium ultrastructure of H. dentata and H. glaucifolia were investigated using the stereo microscope and scanning electronic microscope (SEM). The results were as follows: (1) There were significant differences in floral features between species, especially in the presence or the absence of lateral lobes of petal, morphology of 3-lobed lip, and the length ratio of the spur to the ovary. (2) The ultrastructures of gynostemium were obviously different between the two species, which were shown in shapes of staminode, outer epidermal cells of anther wall, and stigma branch. (3) Exine sculptures of massula were distinguished in two species, the reticulate type in H. dentata, and the baculate → reticulate type in H. glaucifolia. It was suggested that some floral features were selected as potentially valuable for species delimitation, including the presence or absence of lateral petal lobes, variations in spur morphology, the length ratio of the spur to the ovary, and the types of pollen exine sculpture. Additional data on floral features and ultrastructures of gynostemium were reported as supplement for understanding of H. glaucifolia. Notably, it was not confirmed that H. glaucifolia should be treated as an independent genus from Habenaria.

Keywords

• orchidaceae
• floral structure
• gynostemium
• stigma branch
• exine sculpture
• anther sac channel