Abstract: The floral morphs of an invasive herb, Oxalis corniculata, were surveyed based on the examination of herbarium specimens deposited in IBSC, and field observation on living individuals in 24 natural populations in China. The floral phenology, pollen-ovule ratio (P/O) and floral visitors of O. corniculata were investigated and determined. Assisted pollination experiments were carried out to examine the breeding system of O. corniculata. Scanning electron microscope (SEM) and fluorescence microscope (FM) were employed to examine pollen germination and the growth of pollen tubes. The species is composed of three floral morphs in China, viz., the long-styled morph, the semi-homostyled morph, and the quasi-homostyled morph. The semi-homostyled morph is common in disturbed urban and ruderal habitats, whereas only one long-styled population was found in less disturbed habitats of Pinus forests in Anning County, Yunnan Province, although two specimens (in IBSC) of long-styled individuals collected from a same locality in Guangdong Province were also recorded. The flowering period of O. corniculata was from February to November, with a peak at March to September; the longevity of a single flower was two days, and the petals closed at the first night and reopen in the next morning. Pollen grains were found on self-stigmata, and the pollen grains were germinating on the stigmata before the flower opening. The P/O was 83.3±33.08. Nectar secretion was observed but the volume was not large enough to be measured. A small butterfly (Pseudozizeeria sp.) was observed to visit the flowers of semi-homostyled plants, but its effective-ness as a pollinator was extremely low. Fruit set of untreated bagged flowers (88.12±3.38) was not significantly different from that of open flowers (88.03±2.48). Fluorescence microscopic (FM) observations proved that pollen germinated on self-stigmata and pollen tubes grown in self-styles. Measurements of floral traits and results of manipulated pollination treatments indicated that the breeding system of semi-homostyled plants of the species is typical autogamy.

Key words: autogamy, floral morph, heterostyly, Oxalis corniculata, pollination, tristyly