De Valera, Máirín (1912–84), phycologist, was born 12 April 1912 in Dublin, the eldest daughter and second eldest child of seven children (five boys and two girls) of Éamon de Valera (qv) and Sinéad de Valera (qv) (née Flanagan), a primary school teacher. Educated at Holy Faith Convent, Greystones, at Haddington Road, Dublin, and at Loreto College, St Stephen's Green, Dublin, she entered UCD to study science, graduating in botany with a first-class honours degree (1935). She started postgraduate research under the supervision of Professor Joseph Doyle (qv) and completed an M.Sc. thesis (1936) on a comparison of the conifer genera Athrotaxis and Sequoia. Awarded a travelling scholarship, she commenced studies at the University of Leeds (1936–7), but left to pursue an interest in marine algae, first at Aberystwyth, Wales, and then at the Marine Biological Laboratory at Kristineberg, Sweden. Having enrolled at the University of Lund (1937), she worked under the direction of Harald Kylin, an eminent phycologist, publishing several papers on algal morphology and physiology. She returned to Ireland briefly in the summer of 1938 to collect algal material from Galway Bay, and later published a paper based on her identifications (‘Some new or critical algae from Galway Bay, Ireland’, Kungliga Fysiografiska Sällskapets i Lund Förhandlingar, ix/9, 1939).
In 1939 de Valera returned to Ireland to become an assistant in the department of natural history at UCG. As the only botanist on the staff, she taught all of the botanical courses offered to students of medicine and science; her workload doubled when she offered students the option of lectures in Irish. She earned a reputation as a tough examiner and, until the standards of the students taking botany improved, hers was a difficult subject to pass. Because of her heavy teaching load and her isolation from other phycologists, she did not publish many research papers in the years following her appointment, though she continued to carry out fieldwork and published the first record of Asparagopsis armata in the British Isles (Irish Naturalists’ Journal, viii/2, 1942). During the war she was involved in a survey of marine algae as potential sources of agar on behalf of the Industrial Research Council (1943–6); she carried out much of the fieldwork along the west coast of Ireland, travelling by bicycle. Subsequently she wrote the foreword for the publication that resulted from this study – Notes on some common Irish seaweeds (edited by Agnes Brennan, 1950). The information she gathered on the genera Pterocladia and Gelidium during this study formed the basis of a dissertation for which she was awarded a Ph.D. by the NUI in 1945.
Appointed lecturer in botany at UCG in 1947, she began to teach almost the entire honours B.Sc. course in botany, with the exception of plant physiology, through Irish and English. Significantly, she was a co-founder of the British Phycological Society and attended the inaugural meeting at Bangor, Wales (1951). She was elected vice-president of the society (1969) and later made a life member (1977). Her participation in the society renewed her interest and activity in algal research and she carried out field studies of the distribution, ecology, and life histories of several algae, producing a steady stream of papers up to her retirement. She was elected a member of the RIA (1956) and served on several of its committees, including the one that administered the Praeger fund. As secretary of Section A (Biology), she organised the third international seaweed symposium, together with Colm Ó hEocha (qv), and prepared a field guide entitled Topographical guide to the seaweed of Galway Bay for the meeting, which was held at UCG in August 1958. She afterwards wrote a report of the symposium, which was published in the Irish Naturalists’ Journal (xiii/1, 1959). The chair of botany at UCG was established in the early 1960s and de Valera was the first to hold it, from 1962; she remained professor of botany until her retirement in 1977, whereupon she was appointed professor emeritus of the NUI. One of her last major undertakings was to choose the location for a marine field station at Finavarra, Co. Clare, and she was immensely proud when it was finally commissioned.
Throughout her career she devoted herself to teaching and research, and the supervision of her research students. Able to recall field locations of rare and common algae with great accuracy, she had an unequalled knowledge of the species of the west coast of Ireland. Regarded by students as a hard task-master, she demanded high standards in their written and illustrative work and was freely critical of their efforts. Colleagues remembered her as a ‘splendid raconteuse’ (Mitchell) and ‘charming’ (Guiry and Dixon), with a great sense of humour, though she was equally formidable and occasionally exasperating. She had a youthful outlook on life and was generous to her colleagues. Deeply attached to the place where she had worked almost all her life, she bequeathed her herbarium, books, and reprints to the department of botany at her death. The red algal genus Devaleraea was named for her in 1982 by Michael D. Guiry of UCG. She died suddenly 8 August 1984 at her home in Galway; she never married. Guiry and Dixon compiled a bibliography of her publications, comprising twenty-one scientific papers (1985).