Abstract:The floral biology of Acacia auriculiformis A. Cunn. ex Benth. was investigated in a seed orchard at Shadui Town, Jiangmen City, Guangdong Province with the flower morphology observed under light microscopy and scanning electron microscopy (SEM). A. auriculiformis flowered from August to December. Its spike inflorescence consisted of 114.9±11.9 flowers, bearing 124.1±16.5 anthers in each flower. Within each anther existed eight pollen sacs, and eight polyads were produced with 16 pollen grains in each. It thus accounted of 15885 grains per flower. The pistil contained an average of 14.4±1.8 ovules with a smooth, wet stigma and a solid style. Pollen to ovule ratio (P/O) was 1103.1. Anthesis normally began at night and the whole process of flowering could be divided into 5 stages. The phenomena that style emerged from flower bud before stamen and that stamen emerged firstly were all observed during anthesis at different trees, which was inferred that A. auriculiformis was homogamous. As observed under SEM, anther began to dehisce along dehiscent line at stage 2, and completely opened at stage 4. Abundant polyads were released between 9:00 and 12:00. The stigma exudate emerged apparently during the first half-day after anthesis and then decreased gradually. Stigmas started to wilt at 3~4 days after anthesis. The stigma receptivity lasted about 3 days and the peak of receptivity began after 10: 00 at the first day.
