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 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.

[4][5][1] In 1936, a scholarship enabled Baylis to attend London Imperial College where he gained his PhD in 1938 in Plant Pathology.

[4][6][1] His PhD thesis was entitled, "The influence of certain fungi on the germination of peas; and, A physiological study of the pathogenicity of several species of Sclerotinia".

[6] On returning to New Zealand, Baylis joined the DSIR at Lincoln where he researched diseases of linen flax (Linum usitatissimum).

[8][9] Geoff Baylis' research made several important contributions to our understanding of the role of mycorrhizae, or the symbiotic relationship between plant roots and soil fungi.

He moved back to Campbells Bay, next door to the original family home (which he had bought and restored for his nephew Geoffrey Chamberlain).