Genetically based phenotypic differentiation between native and introduced tetraploids of Oxalis pes-caprae

Rapid evolutionary change often plays an important role in determining the success of plant invasions. Oxalis pes-caprae, a geophyte native to South Africa, has become a persistent invasive weed in several areas of the world, being particularly widespread in regions with a Mediterranean climate. The objective of this study was to look for the existence of genetically based phenotypic differences regarding competitive ability between O. pes-caprae native tetraploids and introduced tetraploids recently discovered in the invaded range of the western Mediterranean basin. For this, shoot emergence time, beginning of flowering, chlorophyll fluorescence parameters, aboveground biomass, final offspring bulb production and survival were measured in a greenhouse experiment with plants from both ranges growing alone or in competition with Trifolium repens. Results demonstrated significant differences between introduced and native tetraploids, with plants from the invaded range emerging earlier, beginning flowering later and producing more aboveground biomass and offspring bulbs than South African plants. Furthermore, introduced plants showed an increase in aboveground biomass when grown with T. repens, and affected T. repens growth more severely than their native conspecifics, which may be indicative of a greater competitive ability. These findings provide strong evidence for genetic differentiation between introduced and native tetraploids. It is suggested that founder events and rapid post-introduction adaptive evolution may have contributed, independently or in concert, to this divergence.