John Muir, medical practitioner and naturalist, studied arts and literature at the University of St Andrews (1890-1892) and then medicine at the University of Edinburgh, qualifying as Bachelor of Medicine (MB) and Master in Surgery (CM) in 1896, and as Doctor of Medicine in 1902. He came to the Cape Colony in 1896 and was licensed as a medical practitioner in the Cape Colony in April 1897. At various times he practiced in Worcester, Strydenburg, Sterkstroom (1907), Albertina (1912, 1915), and finally at Riversdale, until retiring in 1923. He was particularly interested in the genetic transmission of haemophilia.
As early as 1912 Muir presented some living specimens of proteas to the South African Museum, Cape Town. In Riversdale, particularly after his retirement, he made an extensive collection of the plants of the region and followed the routes of early collectors. He cultivated aloes and succulents in his garden, which was visited by many botanists. The University of Edinburgh awarded him the degree Doctor of Science (DSc) for a thesis entitled The flora of Riversdale, South Africa. The thesis was subsequently published as a Memoir of the Botanical Survey of South Africa (No. 13, 1929). His plant collection was donated to the National Herbarium in Pretoria, but extensive sets of his plants also went to the Bolus Herbarium at the University of Cape Town, the Compton Herbarium in Cape Town, and the herbarium of the Albany Museum in Grahamstown. The genus Muiria was named in his honour by N.E. Brown*. The plant species named after him include Leucospermum muirii, Erica muirii, Leucadendron muirii, and Conophytum muirii.
Muir also studied the long-range dispersal of plants by ocean currents, by collecting the alien plant seeds and fruits that washed up along the shore. In 1929 he donated his collection of drift seeds to Stellenbosch University, which awarded him an honorary DSc degree that same year. He travelled overseas to study various collections of drift seeds and fruits and published his findings in The seed-drift of South Africa and some influences of ocean currents on the strand vegetation (Memoir of the Botanical Survey of South Africa, No. 16, 1937).
While collecting drift seeds Muir also collected marine shells. He was particularly interested in minute species and the early developmental stages of larger molluscs. His shell collection was donated to the South African Museum. The species Mangilia muiri and Nassa muiri were named after him.
Muir developed an interest also in the common names of plants, birds and shells and in 1926 contributed many Afrikaans plant names for inclusion in the Woordeboek van die Afrikaanse taal. Later he published an article on Afrikaans bird names in Riversdale in The Ostrich (1940) and just before his death contributed a list of Afrikaans shell names for inclusion in the Woordeboek. He also collected historical artefacts and wrote articles on genealogy and popular science, many of them in Afrikaans. In 1905 he married Susanna Charlotta Louisa Steyn, with whom he had a son and a daughter.