Thistle Harris commenced her professional career as a secondary school teacher in 1924. She continued in this role until she was appointed as lecturer in biological sciences at Sydney Teachers' College until her retirement in 1958.
Thistle often expressed the view that 'education of people was the most important pursuit in society' and in all her activities throughout her long professional and post-professional career, education in one form or another was integral with her endeavours.
Dr Stead was a prolific author and published twelve books - the first of which was "Wildflowers of Australia" published in 1938. This publication did perhaps more than any other of its kind to popularise the recognition and appreciation of Australian native plants. It set in motion a chain of events which has established an international appreciation of Australia's flora.
In 1951 she married David G. Stead, noted marine biologist and pioneer conservationist. Thistle was a great admirer of David's work and it was in his honour that she and a colleague, Carmen Coleman, purchased land at Bargo which is now known as Wirrimbirra Sanctuary. This led to the formation of the David G. Stead Memorial Wild Life Research Foundation of Australia, an important environmental education Field Studies Center.
The Stead Foundation and the Sanctuary stand as a memorial to the work of David Stead as well as being a continuing memorial to the environmental education work of Thistle Harris. Her original initiative, continued support and generous financial contributions ensured the existence of the organisation.
Thistle Stead was an active and dedicated participant in the evolving conservation movement. In the 1920s she was a member of the Australian Naturalists Society, in the 1930s she was active in the Australian Forest League and she continued her participation through the Wildlife Preservation Society and the Nature Conservation Council of NSW.
The Society for Growing Australian Plants owes its origins to the work of Thistle Stead. Together with Arthur Swaby she planned its formation, with Thistle taking responsibility for the NSW division. Having planned the meeting, she then organised Bill Hicks into the position of first president of the Society.
Thistle Stead had a prodigious capacity for writing. Her works assisted all who wanted to learn and inspired others to undertake some learning. Wirrimbirra is first and foremost a learning centre. The location of the Field Studies Centre within the Sanctuary has been a considerable achievement. Many people were involved in this achievement not the least being Alan Strom, but it was Thistle's prestige and her ability to convince administration of the need that proved the crucial factor.
Thistle Stead left a great and enduring legacy which will continue to provide enlightenment and pleasure to present and future generations. She will be remembered by all who knew her and knew of her work with great respect for the inspiration that her work provided.
In 1985 the University of Wollongong conferred on her the Honorary Doctorate of Science. In her acceptance speech Thistle noted:
"Man is part of the natural environment. He lives in it; it sustains him both materially and spiritually. He needs the peace and the serenity bushland provides. He cannot fulfil his potential without knowing it intimately...he is of it."
Thistle Stead's life and work show her very strong belief in this maxim .