Population Studies on Acacia melanoxylon R. Br. I. Variation in Seed and Vegetative Characteristics

Abstract

Considerable variation in phyllode shape and size was found between populations of Acacia melanoxylon sampled over the wide geographical range (27° of latitude) of this species in tropical and temperate eastern Australia. Communities sampled range from closed-forest to open-forest and grassy woodland.

Some evidence of relationships between morphological characters of the phyllodes and environ- mental conditions of the collecting site was found, although such relationships are complex and not easily understood. The most important factors determining phyllode shape and size were the distance of the collecting site from the coast, and the seasonal distribution of the annual rainfall. Phyllodes tended to be smaller and more symmetric in the drier inland areas.

Differences were found between seed characteristics of selected populations, although there was no evidence of correlation of these with selected environmental parameters. Seedlings of 17 popu- lations of A. melanoxylon grown under uniform glasshouse conditions showed some differences in leaf morphology. The age at which conversion to phyllodes begins is correlated with the mean annual rainfall at the site of origin of the seeds.

The occurrence of this species in such a wide variety of habitats in eastern Australia is probably due to its clinal variation.