Geoffrey Thomas Sandford Baylis

Geoffrey Thomas Sandford Baylis (24 November 1913 – 31 December 2003), also known as Geoff Baylis or G.T.S Baylis, was a New Zealand botanist and discovered the sole Pennantia baylisiana living on Three Kings Island in 1945.

He earned his MSc on the ecology of the mangrove Avicennia resinifera (now Avicennia marina subsp. australasia). In 1936, a scholarship enabled Baylis to attend London Imperial College where he gained his PhD on fungal damage to germinating peas. In 1946, he was appointed Lecturer-in-Charge of Botany at University of Otago, taking over from the Rev. Dr J. E. Holloway. He became first Professor of Botany (1952) and was Head of the Department for 34 years, retiring in 1978.

He was elected a Fellow of the Royal Society of New Zealand in 1961, and attended his last Fellows' AGM on his 90th birthday, as one of the two longest serving living fellows. He served on the Otago Museum Trust Board as the University's Representative. He received the Society's Hutton Medal in 1994; he was a foundation and life-long member and President of the New Zealand Ecological Society; and in 1997 he was elected an Associate of Honour of the Royal Horticultural Institute of New Zealand.

The annual Geoff Baylis Lecture was established by the Botanical Society of Otago in 2002 to honour his contributions to the society and field of botany.

The standard author abbreviation G.T.S.Baylis is used to indicate this person as the author when citing a botanical name.