Darling Range Branch, 14 February 2026

Alex George AM, a well-known botanist, was invited to DRB to share his observations of unexpected and widespread colour changes and growth patterns in Australian native plants, particularly shrubs and trees in bushland environments during autumn. These changes were observed during periods of unusual climatic conditions, including very dry summers and delayed rainfall. In many locations, large numbers of plants changed colour simultaneously, far beyond what George had previously seen, raising concerns that vegetation might be dying or suffering long-term damage.

A key insight from George’s observations was that many of these colour changes were temporary. After rainfall or improved seasonal conditions, some plants recovered and returned to green foliage. This indicated that the plants were responding to environmental stress rather than experiencing irreversible decline. Notably, the phenomenon did not occur every year, suggesting it was triggered by specific combinations of stressors rather than normal seasonal change.

The colour changes included shifts from green to red, bronze, golden, or mottled patterns. Unlike the autumn leaf colour changes of deciduous plants in the northern hemisphere, these changes did not usually involve leaf drop. Leaves often remained attached and later regained their green colour. George noted the absence of an established scientific term to describe this reversible process, proposing that it represents a dynamic physiological state rather than senescence or death. For this, he coined the term diallagy.

These changes were observed across a wide range of species and plant families, with different species responding at different rates. Some plants reverted to green within days, while others took weeks. George suggested that multiple biological mechanisms may be involved, including temporary loss or reorganisation of chlorophyll, alteration of chloroplasts, and the production of protective pigments. Despite its widespread occurrence, the process remains poorly researched.

Fire ecology was another major theme of the talk. Many Australian plants are adapted to fire, with some re-sprouting afterwards and others relying on fire to trigger flowering, seed release and germination. Post-fire landscapes often display rapid regeneration and flowering that may not occur under normal conditions. Some species remain dormant for years and only emerge after fire, demonstrating specialised survival strategies.

George also highlighted unexpected seasonal growth, noting that some plants initiate new growth or structural changes during summer, traditionally considered an unfavourable time for growth. These responses further demonstrate the resilience and adaptability of native flora.

Overall, the talk emphasised that plant behaviours which appear unhealthy at first glance are often adaptive responses to stress. George concluded by stressing the need for further scientific research, particularly as climate variability increases, and shared anecdotes from his time at the herbarium, including collecting wildflowers preserved in thick ice for public display.

Species mentioned during the talk were:

Recorded by Rob Sandri and Written by Arlene Quinn using AI Support