William Gilson Farlow (1844-1919), eminent mycologist and phycologist and first Professor of Cryptogamic Botany in North America, bequeathed his library, herbarium, manuscripts, and notes to Harvard in 1919. His personal collection of books and journals, many of them rare and now unobtainable, form the nucleus of the Farlow Reference Library. The collection, worldwide in scope, includes works on the identification and classification of algae, fungi, mosses, and lichens.

The Library opened at its present location at 20 Divinity Avenue in 1924 and has continued to grow. Further bequests include the library of Roland Thaxter (1858-1932), as well as manuscripts, correspondence, illustrations and field notes of several other Cryptogamic botanists including E.B. Bartram, E.A. Burt, W.H. Weston Jr., D.H. Linder, and I.M. Lamb. More information on collections of specific personal papers is currently being made available. Check the Farlow archival finding aids page for updated lists.

The Farlow Reference Library of Cryptogamic Botany (FH) specializes in organisms that reproduce by spores, without flowers or seeds. Subject areas cover fungi, bryophytes, lichens, algae, and pre-Linnean works. The library's holdings appear in Harvard Libraries online catalogues, HOLLIS and HOLLIS for Archival Discovery as Botany Farlow Library. The Farlow stacks are closed and the collection is non-circulating. Materials may be consulted in the Farlow reading room Monday-Friday from 9:30 a.m. - 12 p.m. and in the Botany Libraries' main reading room Monday-Friday from 9 a.m. - 5 p.m.