Effects of Variation in Floral Morphology on Pollination Mechanisms in Asclepias Tuberosa L., Butterflyweed (Asclepiadaceae)

Abstract

Field observations revealed the presence of fruit‐producing (fruiting) and non‐fruit‐producing (non‐fruiting) plants in two south central Oklahoma populations of Asclepias tuberosa L. Comparative measurements of floral characteristics between fruiting and non‐fruiting plants indicated that fruiting plants have significantly larger alar fissure widths and a greater percentage of intact pollinaria. The smaller alar fissure width on flowers of non‐fruiting plants apparently reduces the probability of successful pollinia insertions in these plants. Greater numbers of observed pollinia insertions into fruiting‐plant fissures appear to be the result of the increased likelihood that pollinia, which are significantly narrower than the fissures of fruiting plants, will be inserted into fruiting‐plant fissures than those of non‐fruiting plants. Apparently non‐fruiting plants act primarily as pollinia donors while fruiting plants act primarily as pollinia recipients. These characteristics of butterflyweed tend to promote a dimorphic, allogamous type of pollination.

The adaptedness of the floral phenotype in a relict endemic, hawkmoth-pollinated violet. 1. Reproductive correlates of floral variation

“…These investigations have often shown that variation in the size of flowers or floral parts translates into differences in seed production and outcrossing rate (erg. Beare & Perkins, 1982;Harder et al, 1985;Thomson & Stratton, 1985;Nilsson, 1988).…”

Bumble Bee Pollination and Floral Morphology: Factors Influencing Pollen Dispersal in the Alpine Sky Pilot, Polemonium Viscosum (Polemoniaceae)

“…A CENTRAL POSTULATE of the theory of plant/ pollinator coevolution is that the size, arrangement, and shape of flower parts have evolved to improve the efficiency of pollination or the number ofpollen grains delivered to the stigma surface during a pollinator visit. This view has been elaborated by Stebbins (1971) and supported by many empirical studies (e.g., Beattie, 1971;Beare and Perkins, 1982;Waser and Price, 1984;Thomson and Stratton, 1985;Galen and Newport, 1987;Campbell, 1989). In contrast to effects on female reproduction, the relationship of flower form to male components of reproductive success has received less attention (but see Campbell, 1989).…”

Pollination genetics of the common milkweed, Asclepias syriaca L.

“…Its unusual pollination system, found in the Asclepiadaceae and Orchidaceae, allows pollen removal, receipt and presence on pollinators to be readily quantified (e.g. Macior, 1965;Kephart & Heiser, 1980;Beare & Perkins, 1982;Morse, 1982;Wolfe, 1987). In the Asclepiadaceae, numerous pollen grains are clustered 102 J.S.SHORE in pollinia which are commonly dispersed in pairs (as pollinaria).…”