While most lichenicolous fungi belong to the Ascomycota, c. 5% of them are members of the Basidiomycota. Among these, the poorly known genus Crittendenia in the Pucciniomycotina has recently been described for lichenicolous fungi with minuscule needle-like synnematous basidiomata. Although only two species were hitherto known, the wide observed host-spectrum suggested a larger number of mainly host-specific species. A classical revision using morphological characters alone proved to be virtually impossible, because of the large variability of the material from each host genus, and the scant morphological differences between hypothetically distinct species from different hosts. We studied over sixty specimens and made a large number of measurements of the available morphological characters. We additionally generated 18 ITS and 21 nuLSU rDNA sequences and conducted maximum likelihood and Bayesian analyses. We also performed one species delimitation analysis (bPTP-ML). By combining sometimes subtle morphological differences, host choice and phylogenetic results, we were able to accept eighteen morphologically and/or genetically distinct species, all confined to a single host genus or to several closely related host genera. Two further putative species are left unnamed, as richer material is needed and molecular data are missing. Sixteen new species are described: Crittendenia absistentis (on Bacidia absistens), C. bacidinae (on Bacidina apiahica), C. bryostigmatis (on Bryostigma muscigenum), C. byssolomatis (on Byssoloma maderense), C. crassitunicata (on Melanohalea ushuaiensis), C. heterodermiae (on Heterodermia comosa), C. hypotrachynae (on Hypotrachyna), C. kakouettae (on ‘Byssoloma’ kakouettae), C. lecanorae (on Lecanora), C. lecidellae (on Lecidella elaeochroma), C. lopadii (on Lopadium disciforme), C. parvispora (on Bacidia), C. physciiphila (on Phaeophyscia, Physcia and Physciella), C. physconiae (on Physconia distorta), C. stictae (on Sticta fuliginosa) and C. teloschistis (on Teloschistes). Further, a ML analysis of the Agaricostilbomycetes using ITS and nuLSU sequences suggested that Crittendenia cannot be included in any known family, and the new family Crittendeniaceae is therefore described for the genus. Keywords: Basidiomycetes, Chionosphaera, Crittendeniaceae, heterobasidiomycetes, lichenicolous fungi, phylogeny, taxonomy.