Geoffrey Thomas Sandford Baylis (24 November 1913 – 31 December 2003) was a New Zealand botanist and Emeritus Professor specialising in plant pathology and mycorrhiza. He was employed at the University of Otago for 34 years undertaking research into plant and fungal ecology and symbiotic interactions, taxonomy and anatomy. He collected hundreds of plant specimens in the field and founded the Otago Regional Herbarium (OTA). He discovered the sole Pennantia baylisiana living on Three Kings Island in 1945, and was elected as a Fellow of the Royal Society of New Zealand in 1961.