Phylogenetic relationships among species of Percina are unresolved. Previous sys-tematic studies of Percina have resulted in the recognition of nine subgenera, di-agnosed by external morphological characters. Throughout the history of darter taxonomy characters such as large body size, high meristics, drab coloration, and exploitation of a hyperbenthic habitat have been interpreted as pleisiomorphic. Most species of Percina exhibit these characters, and have been hypothesized to represent the ''primitive'' lineage of darters. The hypotheses that each of the poly-typic subgenera of Percina are monophyletic and that the previously defined primi-tive characters are pleisiomorphic, have not been investigated with cladistic analyses. In this investigation, complete gene sequences of the mitochondrially encoded cy-tochrome b were collected from a total of 79 individual specimens, representing nine of 10 percid genera and all 40 species of Percina. Observed patterns of cyto-chrome b evolution were very similar to those previously reported in other percid fishes. Maximum-parsimony and maximum-likelihood analyses were generally con-gruent. The majority of subgenera (Percina, Imostoma, Cottogaster, Swainia, and Odon-topholis) were recovered as monophyletic in most analyses. The subgenera Alvordius, Hadropterus, and Ericosma were never recovered as monophyletic; however, mono-phyly of Hadropterus and Ericosma could not be rejected in statistical analyses of maximum-likelihood score differences. As a result of these phylogenetic analyses, a novel classification of Percina species is proposed. The use of subgenera in Percina taxonomy is abandoned in favor of the recognition of monophyletic ''species clades.'' Reconstruction of character evolution on the hypothesized phylogenetic relationships suggest that previously identified pleisiomorphic character states in darters may actually be derived within Percina. Hypothesis testing of derived and ancestral traits in darters is complicated by uncertainty in ancestral character state reconstruction. Contributing to the lack of confidence in character optimization are inadequate sampling of Etheostoma species, short internal branches on the phylog-eny, and a high frequency of character change across the entire diversity of darters. W ITH over 180 species, Percidae is the sec-ond largest family of freshwater fishes in North America, and all but three species of North American percids are darters (subfamily Etheostomatinae). Evidence from morphology (Wiley, 1992), behavior (Page, 1985), and mtDNA sequence data (Song et al., 1998) indi-cate that darters are monophyletic. Relation-ships among genera, subgenera, and most spe-cies, however, remain unresolved. Percina is the second largest genus (40 spe-cies) of darters. Phenetic analyses of external morphological characters have been used to classify species of Percina into nine subgenera (Page, 1974, 1981). Most of the characters con-sidered were meristics, morphometric ratios, and pigmentation patterns (Page, 1974, 1981). There is no published cladistic investigation of relationships among species of Percina using dis-cretely coded morphological characters (i.e., os-teology). Percina has been hypothesized to include the plesiomorphic darters (Jordan et al., 1930; Page, 1974; Bailey and Etnier, 1988). Unlike other darter genera, species in Percina exhibit both hypothesized derived and ancestral char-acteristics. For example, Percina lenticula has been regarded as the most ''primitive'' species of Percina (Page, 1974), because it lacks bright breeding colors, has high meristics, and is the largest darter species (Page, 1974; Page and Burr, 1979). On the other hand, Percina roanoka