Breeding system, floral biology and pollinators of Sagittaria montevidensis subsp. montevidensis Cham. et Schlech. (Alismataceae)

Abstract

Sagittaria montevidensis is a common marsh species with showy flowers and of interest to humans; however, its sexual reproduction is mostly unknown. The floral biology, pollination and breeding system were studied in two coastal populations of De La Plata river in Argentina. Blooming and fruiting occurred throughout the year. The staminate (more abundant) flowers (with pistillodes, empty or with rudimentary ovules) and the pistillate flowers (with staminodes), are usually located in distinct whorls. Protogyny was common and all the floral pieces showed hydrophobicity.Both flower types experienced three stages during the three days of anthesis. The staminodes and staminal filaments had nectar secretory papillae, and nectar accumulated at the base of the petals. Osmophores in the reproductive organs and petals emitted sweet and light aroma. In the visible spectrum, petals appeared white, with a dark reddish spot widening towards the region of nectar accumulation; in the UV spectrum, reflecting nectariferous regions contrasted with the other floral parts. Both flower types exhibited similar visual patterns, the less osmophore-bearing and nectar producing pistillate flowers resembled the more rewarding (pollen and nectar producing) staminate ones. The bowl-type flowers were pollinated by four species of medium-sized bees from two families and visited by nectar and pollen thieves, florivores and frugivores from five Insect orders. The low degree of self-compatibility and high reproductive success by open pollination confirmed that sexual reproduction was frequent.