Stigma, pollen tube transmitting tract, and epidermal micromorphology of the style of Sarracenia purpurea (Sarraceniaceae)

Abstract

Entomophilous flowers of the genus Sarracenia have a unique umbrella-shaped style, which consists of a broadened and flattened umbrella canopy and a thin cylindrical umbrella stalk. Anatomical and micromorphological features of the style of Sarracenia purpurea L. were studied using light microscopy and scanning electron microscopy. This study found that the pollen tube transmitting tracts (PTTTs) start as a semi-solid canal filled with endotrophic conducting tissue, and run from the peripheral to the center of the canopy where the PTTT becomes a hollow canal supported by ectotrophic conducting tissue. The presence of stomata on the epidermis of the canopy and chloroplasts in its ground parenchyma indicate photosynthetic activities. Convex epidermal cells with intense cuticular striations on the canopy that are similar yet different from those on various regions of the sepals and petals indicate that it may provide contrasting visual cues for pollinators. Multicellular secretory glands and trichomes, which may provide olfactory cues and tactical cues respectively, are also found on the canopy. Thus, the stylar umbrella not only serves as a region for pollen grain capture, pollen germination, and pollen tube transmission but may also play an important role during pollinator–flower interactions.