The few sites where this fern remain tend to be in isolated mountainous locations where pickers never found it. Although the strawberry tree (Arbutus unedo) is relatively common in the park, it is one of Ireland's rarest native tree species and is found in very few locations outside Killarney. In the park it is found on cliff tops and the edges of the woodlands around the lake. Killarney whitebeam (Sorbus anglica) is a shrub or small tree that grows on rocks close to lakeshores. It is found only in Killarney. The more common Irish whitebeam (Sorbus hibernica) is also found in the park. The greater butterwort (Pinguicula grandiflora) (also known as the Kerry violet) is a carnivorous plant found in bogs. It digests insects to supplement the poor supply of nutrients (especially nitrogen) available from the bog. Its purple flowers bloom in late May and early June. Irish spurge (Euphorbia hyberna) is an Atlantic species that in Ireland is only found in the southwest. In the past the milky sap from its stem was used to cure warts. Fishermen used it to capture fish, utilising compounds in the sap that prevent fish gills from functioning properly and so suffocate the fish. A number of rare species of myxomycete fungus have been recorded in the park. These are Collaria arcyrionema, Craterium muscorum, Cribraria microcarpa (the only known location in Ireland), C. rufa, C. violacea, Diderma chondrioderma, D. lucidum, D. ochraceum, Fuligo muscorum, and Licea marginata. The park has a highly diverse lichen flora. Fauna Mammals Most mammals native to Ireland and long established introduced species are found in the park. The bank vole was first identified in 1964 in northwest Kerry. Its range has now expanded and now includes the park. Pine marten is another notable species in the park. Deer The park has Ireland's only remaining wild herd of native deer (Cervus elaphus), comprising approximately 900 individuals. an increase from less than 100 individuals in 1970. They are found in upland areas of the park, mostly on Mangerton and Torc mountains. This herd has been continuously in Ireland for 4,000 years, since the return of red deer to the island, possibly aided by humans, after the last ice age, approximately 10,500 years ago. They were protected in the past by the Kenmare and Muckross estates. The herd is not completely pure because stags were introduced to the herd to improve