Experiments

THE COLEUS PROJECT

Participants: Joe Holtum (JCU), Klaus Winter (STRI)

Prologue: I am studying plants from three genera of African origin that arrived in Australia or New Zealand after Africa, Australia and New Zealand separated from Gondwana i.e. the African ancestors crossed the Indian Ocean by some means. In Africa, there are members of each of these genera, Bulbine, Bulbinella and Coleus, that exhibit CAM photosynthesis. It is unknown whether the Antipodean relatives exhibit CAM nor whether CAM, if present, differs in its expression from CAM in the current African taxa i.e. whether the expression of CAM was modified in response to Australian and New Zealand conditions, or perhaps restricted by a genetic bottleneck.

Project: The 20+ species of Coleus (Fam. Lamiaceae) in Australia are descended from probably a single African ancestor that crossed the Indian Ocean. The aim is to survey Australian Coleus for CAM photosynthesis and to compare any expression of CAM with that by African species I can get my hands on. This project will take a while.

Progress: I have measured plant-CO₂ exchange and day-night leaf titratable acidity during watering, droughting and re-watering cycles in the Australian species C. apreptus, C. foetidus, C. graveolens and C. magnificus. Low level CAM has been detected in all. I am currently studying C. amoenus. Low-level CAM has also been observed in C. amboinicus, native to Africa and the Arabian Peninsula.