New Zealand botanist and explorer who was employed by the Auckland Museum where she succeeded L.M. Cranwell (1907-2000). During the Second World War she was a volunteer in the Women's Auxiallary Air Force, subsequently training in tropical botany in Malaysia and working for many years in the Singapore Botanic Gardens.

In 1947 she met and married Geoffrey Allen (-1985), a pilot, wildlife photographer and amateur ornithologist. During the 1948-1960 State of Emergency, Betty and her husband took shelter from Communist guerillas in the forest, using the time profitably to collect plants. She made plant collections both under her maiden and married names, the latter often cited as 'Molesworth-Allen'.

Betty Allen retired with her husband to Los Barrios in Andalucia, Spain (1963) where she continued to collect plants, particularly ferns. It was in 1965 that she made the remarkable discovery of Psilotum nudum (L.) P. Beauv. in southern Spain, previously thought to be exclusively a tropical species. Betty Allen contributed to Flora Europaea and published on the flora of the region. The hybrid Narcissus x alleniae was named in her honour. She was awarded the MBE in 1997.