Distribution, growth analysis and reproductive biology of Cape ivy (Delairea odorata Lem. syn Senecio mikanioides Walp.) in California

The distribution, growth and reproductive biology of Cape ivy ( Delairea odorata Lem. syn. Senecio mikanioides Walpers) was the focus of this research. Cape ivy, a vine native to South Africa, is an invasive weed expanding its range in coastal California. A distribution map of California Cape ivy was created, and locations of stipulate or non-stipulate morphological types were compiled. We found Cape ivy occurring in seven plant community types, and predicted that it should occur in five more, refuting the assumption that Cape ivy is an exclusively riparian weed. GIS analysis indicated that in California Cape ivy occurs at elevations between 0 and 891 m, at annual mean temperatures between 10.5 and 17.7°C and in areas with annual precipitation between 232 and 2270 mm. CLIMEX and GARP computer models predicted Cape ivy's potential expansion into moist areas of the San Joaquin Valley and Sierra Nevada foothills. A growth analysis study of four Cape ivy populations grown at varying shade levels gave insight into its genetic structure and growth requirements. Results indicated that there was phenotypic plasticity in growth response to light levels, and that genetic variation was present among and within populations. The growth experiments showed that Cape ivy could survive in shaded areas of inland California that receive sufficient summer moisture. The third research area was Cape ivy reproductive dynamics and seed biology. Cape ivy was shown to be self-incompatible and able to produce viable seed throughout California. Over a three year period, seed from a wide geographic range of populations was sampled and 66% of 104 locations produced viable seed. Seeds weighed between 0.02 and 0.39 mg, and the highest percentage of germination occurred in seeds above 0.20 mg. Optimal germination occurred between 17 and 25°C and seeds germinated in light or dark. Seeds germinated when planted on the soil surface or when buried 1 cm, but did not emerge from deeper burial. Similarly, stem fragments on the soil surface or buried 2 cm emerged, but those buried deeper did not. The final chapter concludes with a discussion of the management implications of viable, wind-dispersed seed production.