Matilda Cullen Knowles (31 January 1864 – 27 April 1933) is considered the founder of modern studies of Irish lichens following her work in the early twentieth century on the multi-disciplinary Clare Island Survey. From 1923 she shared curatorship of the National Museum of Ireland herbarium – a collection of dried and pressed plants now housed at the National Botanic Gardens. Her work is said to have "formed an important baseline contribution to the cryptogamic botany of Ireland and western oceanic Europe".