Aspects of the Floral Biology of Allocasuarina verticillata (Casuarinaceae)

Abstract

Aspects of the floral biology of Allocasuarina verticillata were recorded in a natural stand in Canberra, Australia. The trees are dioecious, and flowering took place during the autumn to spring months (May–October). The female inflorescence consists of over 100 individual flowers, which remained receptive for up to 12 weeks. The proportion of individual flowers pollinated increased gradually over this time. The advantage of a long female receptive phase is that each inflorescence can potentially receive pollen from a number of male sources. Duration from pollination to fertilisation was 53–83 days. Male inflorescences dehisced over a 3–9 week period depending upon air temperatures. Pollen germination was highest at 10˚C and 15˚C and poor at 5˚C, 20˚C and 25˚C. Pollen grains remained turgid at the lower temperatures for at least 3 days. Seed germinated well at temperatures between 10˚C and 25˚C but there was a marked decline at 30˚C. Stratification of seed is suggested as a standard practice in germination tests. Results are discussed in relation to developing tree improvement strategies for domestication of the family Casuarinaceae.