Multiple lines of evidence clarify limits of Allocasuarina thalassoscopica, A. defungens and A. littoralis (Allocasuarina sect. Cylindropitys, Casuarinaceae)

Abstract

Uncertainty in identifying Allocasuarina shrubs of the North Coast botanical region of New South Wales and south-eastern Queensland prompted investigation of species limits using morphological and cytological data. PATN analysis using 36 morphometric characters, seedling morphology and cytogenetic analysis supported the existing circumscription of A. defungens and A. simulans. Trees of A. littoralis were observed throughout the study area and the distinct morphology of the diploid and polyploid forms is noted. Further work is required to establish whether these differences are consistent over the full range of the species. Shrubby plants of A. sect. Cylindropitys, other than the above species, growing along the NSW North Coast are currently known by several names, including A. defungens×A. littoralis. These plants were found to be morphologically most similar to A. emuina and A. thalassoscopica from south-eastern Queensland and to have similar phenotypes. Allocasuarina thalassoscopica is recircumscribed on morphological characters to encompass these shrubby plants in New South Wales and A. emuina and A. thalassoscopica from south-eastern Queensland. A key is provided for identification of plants of A. sect. Cylindropitys. Counts of chromosomes found that recircumscribed A. thalassoscopica is tetraploid and A. defungens is triploid at Nabiac but tetraploid at Khappinghat Nature Reserve. The results of the present study are consistent with a hypothesis of parallel evolution, which is possibly due to edaphic factors and requires further study.