Gender Variation of Sequential Inflorescences in a Monoecious Plant Sagittaria trifolia (Alismataceae)

Abstract

In protogynous plants, female flowers of early blooming plants are at a reproductive disadvantage because they cannot set fruit due to the lack of available pollen. To study this phenomenon, gender expression of the monoecious herb Sagittaria trifolia was investigated over the entire flowering season in two field and two cultivated populations in Hubei and Hunan Provinces, China. In racemes of S. trifolia, flowers open sequentially from bottom to top, with female flowers opening first followed by male flowers. This creates a temporal separation of sexes in the species. Under field conditions small plants are often male, with production of both male and female flowers increasing with plant size. Femaleness increased among sequential inflorescences since female flower production increased whereas male flower production did not. Seed production was greater in large inflorescences because they contain more female flowers, and the number of ovules increased in female flowers at basal positions within the raceme. A consistent pattern of high seed set was observed in flowers from both field and cultivated populations. About 1 % of unfertilized ovules resulted from no pollination and 2 % of the seeds produced were only partly developed due to resource limitation. In the first inflorescence of the six experimental populations, 6.7-40.0 % of individuals produced only male flowers, and female flowers of 1.9-6.5 % individuals were aborted. The occurrence of male flowers in early blooming inflorescences could be an adaptive strategy to conserve resources and enhance pollination of female flowers in protogynous S. trifolia.

Flower dimorphism and the maintenance of andromonoecy in Sagittaria guyanensis ssp. lappula (Alismataceae)

“…These monoecious species secrete floral nectar and are visited by generalist pollinators. For example, pollination rate and seed set per flower in S. trifolia were higher than 96% in both field and cultivated populations (Huang et al, 2002). The lower height and lack of nectar in S. guyanensis is probably related to low levels of pollinator visitation.…”

Gender plasticity in Sagittaria sagittifolia (Alismataceae), a monoecious aquatic species

“…However, little is known about the plasticity of reproductive traits, or the factors regulating gender expression. We were particularly interested in investigating S. sagittifolia because recent work on S. latifolia and S. trifolia, two widespread species that superficially resemble S. sagittifolia in both morphology and ecology, indicates striking variation in gender within and among populations (Sarkissian et al 2001, Huang et al 2002. For both of these species, this variation involves considerable reproductive plasticity, including evidence within monoecious populations of size-dependent gender modification (Sarkissian et al 2001, Huang et al 2002.…”

Análise morfológica de Sagittaria montevidensis desenvolvida em diferentes condições de inundação

“…lancifolia (Pimenta, 1992) e S. trifolia (Huang et al, 2002). Esta última 1/ Altura da lâmina d'água.…”

“…A dicogamia e antese seqüencial criam uma separação temporal de maturação dos esporângios e dos gametângios (Huang et al, 2002), favorecendo a fecundação cruzada e evitando a geitonogamia (Bertin, 1993).…”

“…Quanto maior o tamanho da planta, maior número de flores megasporangiadas foi produzido (Huang et al, 2002;Dorken & Barrett, 2003).…”