The museum holds over 59,000 specimens in its herbarium, collected from the mid-nineteenth century onwards. It includes the extensive Cumbrian collection acquired from the University of Lancaster.

The collections consist mainly of study material of flowering plants, ferns, mosses, and seaweeds, amounting to some 24,000 specimens. About 30 individual collections are represented. Some of the earliest material is the Stevens Lakeland collection, of mid-nineteenth century origin. Other important local collections include those of G. Adair, J. Curwen, E. Glaister, T.S. Johnstone, Bishop Goodenough, T.C. Heysham, C.W. Muirhead and D.A. Ratcliffe.