Plants can be categorised by their growth response to temperature, and several studies have demonstrated that more than one thermal type is represented in Australian Mediterranean environments (e.g. Specht et al. 1981) Specht and colleagues (Specht and Dettmann 1995, Specht and Specht 1999) suggest that the overstorey species in Mediterranean Australia have undergone little change since the warmer early Tertiary and have retained a mesotherm (subtropical) growth rhythm with peak growth in late spring/summer. However, Specht and Dettmann (1995) explain that the understorey stratum has more recently evolved an intricate leaf distribution structure which helps to synchronise the growth of this stratum with the cool winter/spring, season of the Mediterranean climate (a microtherm rhythm). The intricate structure increases the plants boundary layer, impeding heat dissipation and effectively raises the temperature of the growing apices, compensating for the cooler environment.

The grasstree Xanthorrhoea preissii Endl., from south-western Australia presents an unusual Mediterranean species that appears to be a poor fit for the theory described above.


Published in Full, Xanthorrhoea, grasstree, temperature, mesotherm, evolution


The MedEcos XI: conference proceedings may be accessed from the National Library of Australia here

This article from the MedEcos XI: conference proceedings may be accessed from the Department of Environment and Conservation library database here