Matilda Cullen Knowles (31 January 1864 – 27 April 1933) is considered the founder of modern studies of Irish lichens[1] following her work in the early twentieth century on the multi-disciplinary Clare Island Survey.

Her work is said to have "formed an important baseline contribution to the cryptogamic botany of Ireland and western oceanic Europe".

[3][4] Her early interest in botany was encouraged by her father, William James Knowles, himself an amateur scientist who would take Matilda and her sister to meetings of the Belfast Naturalists field club.

[1] In 1895 she was introduced to the Derry botanist Mary Leebody and together they worked on a supplement to Samuel Stewart and T.H.Corey's 1888 book the Flora of the North-east of Ireland.

Knowles had gathered the knowledge and experience to do this whilst diligently assisting with a survey of Clare Island as suggested by Robert Lloyd Praeger.

This novel survey involved not only Irish but also several European scientists including prominent UK lichenologist, Annie Lorrain Smith.

[12] Several lichen species have been named in honour of Knowles, including: However, *Acarospora knowlesii C.W.Dodge (1968)[15] is named for geologist Paul H. Knowles of the U.S. Antarctic service, who collected the type specimen in 1940 (note the masculine ending),[16] and *Meliola knowltoniae Doidge (1924)[17] and *Septoria knowltoniae Verwoerd & Dippen.