Abstract
In the flora of south-western Australia, vegetative colour change in summer and autumn followed by regreening after rain is much more widespread than previously reported, though patchy in occurrence and variable within species. The term diallagy (adj. diallagous) is proposed to describe the strategy of reversible change between the green and coloured states. It is here recorded for 99 species in 59 genera of 24 families of flowering plants, both monocots and dicots. These species occur in a number of widely distributed habitats. In some species, extent of colour change increases as long as the dry weather continues. The change generally is reversed after 10-15 mm or more of rain falls over a short period (24 hours). Regreening takes from several days to several weeks. The mechanisms operating within the plants are yet to be investigated, but possibilities are discussed to point the way to further research; some are likely to be similar to that reported for Borya. In an extreme dry summer such as that of 2000-2001, death occurs in some species. Paradoxically, other species flower at this season, in some cases close to diallagous species. It is suggested that these have retained a summer/autumn flowering period (from a tropical origin) to take advantage of pollinators at a season when few sources of nectar and pollen are available.
