Breeding System and Reproductive Success of Thryptomene calycina (Myrtaceae)

Abstract

Thryptomene calycina (Lindl.) Stapf is a small bush with a long flowering period in winter. Hundreds of small flowers open at one time. Its breeding system is highly self-incompatible, with an index of Self-Incompatibility of 0 - 0.1. The site of arrest of self-incompatible tubes is near the micropyle. In wild populations the natural seed set varies between 9 and 13%. Pollination is not a factor limiting seed set in these flowers since every stigma examined from wild populations carried some germinated pollen grains. The low level of seed production is because most pollinations are probably ineffective selfs which occur when pollen exudes from pores in the anthers directly over the stigma; air currents and rain splashing probably accentuate the effect. Self-pollination is facilitated by the long period of stigma receptivity which occurs for 12 days commencing 2 days after anthesis. Each flower contains 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 shed 3 days after anthesis, but this depends on temperature, relative humidity and probably the water potential of flowers. The flowers are visited by few flying insects during most of the flowering season. In warm weather near the end of flowering a wide range of insects visit the flowers. Although the visitors are mostly small flies these are ineffective pollinators. The main potential pollinators are medium sized flies and bees.