The toxicity of Xanthorrhoea johnsonii methanolic leaf extract was investigated using the Artemia franciscana nauplii bioassay. At 24 h, the extract produced an EC(50) of 361.0 ± 41.8 μg/ml, indicating that it was substantially more toxic than the pesticide Mevinphos (1346.2 ± 80.1 μg/ml) and approximately 4 fold less toxic than potassium dichromate (87.1 ± 5.2 μg/ml). Whilst potassium dichromate LC(50) values remained constant across the 72-h test period, these values decreased for the extract and Mevinphos to similar values (199.8 ± 60.5 and 114 ± 12.8 μg/ml, respectively), indicating their similar level of efficacy. Noteworthy was the apparent anesthetic effect of X. johnsonii leaf extract. Although the extract initially appeared to kill the A. franciscana nauplii, they were seen to temporarily recover by 48 h only to die by 72 h.
Keywords: Australian plants; Xanthorrhoea johnsonii; grass tree; methanol extracts; toxic plants.