A Comparison of Breeding Systems and Seed Physiologies in Three Species of Portulaca L.

Abstract

Portulaca oleracea L. is a weed of open agricultural habitats. This paper evaluates the contribution of the plant's breeding system and seed physiology to its success as a weed by comparing these aspects of adaptation with the same aspects in two other species of Portulaca, P. grandiflora Hook., a cultivar, and P. pilosa L., a plant of comparatively limited distribution. Self—compatibility, and the seed characteristics of longevity, resistance to digestive processes, the lack of after—ripening, and overwintering proficiency combine to give the plant quick—response capability when conditions surrounding the seed are capable of supporting growth to maturity. Portulaca oleracea belongs to th group of weeds whose have specific germination requirements for environmental factors. When sufficient water is present, the majority of dormant seeds germinate upon exposure to light and to temperatures >20°C. Portulaca grandiflora seeds germinate equally well in light or dark and demonstrate a wide tolerance to temperature. Portulaca pilosa seeds require light and a temperature of 25°C for maximum germination percentages. These factors of seed production and seed physiology interact to produce large populations of P. oleracea plants that can quickly exploit open habitats that are continually supplied by man.