BREEDING SYSTEM AND REPRODUCTIVE SUCCESS OF THRYPTOMENE-CALYCINA (MYRTACEAE)

Thryptomene calycina (Lindl.) Stapf is a small bush with a long flower ing period in winter. Hundreds of small flowers open at one time. Its breeding system is highly self-incompatible, with an index of Self-Inc ompatibility of 0 - 0.1. The site of arrest of self-incompatible tubes is near the micropyle. In wild populations the natural seed set varie s between 9 and 13%. Pollination is not a factor limiting seed set in these flowers since every stigma examined from wild populations carrie d some germinated pollen grains. The low level of seed production is b ecause most pollinations are probably ineffective selfs which occur wh en pollen exudes from pores in the anthers directly over the stigma; a ir currents and rain splashing probably accentuate the effect. Self-po llination is facilitated by the long period of stigma receptivity whic h occurs for 12 days commencing 2 days after anthesis. Each flower con tains approximately 60 000 pollen grains that are viable for up to 15 days. The pollen-ovule ratio is high, up to 32 000. Most pollen is she d 3 days after anthesis, but this depends on temperature, relative hum idity and probably the water potential of flowers. The flowers are vis ited by few flying insects during most of the flowering season. In war m weather near the end of flowering a wide range of insects visit the flowers. Although the visitors are mostly small flies these are ineffe ctive pollinators. The main potential pollinators are medium sized fli es and bees.