The siliceous scales of 30 mallomonadacean taxa were identified and counted from the surficial sediments of 38 Adirondack lakes. The scales were usually abundant and were always well preserved. The Adirondack flora is typical of acidic to circumneutral oligotrophic lakes. Common taxa include Mallomonas acaroides, M. caudata, M. crassisquama, M. hamata, M. pseudocoronata, M. punctifera, Synura echinulata, S. petersenii, S. sphagnicola, S. spinosa, and Chrysosphaerella longispina. The abundance of certain species (e.g., Mallomonas hindonii, M. hamata) appears to be a reliable indication of acidic waters. Reciprocal averaging (RA) ordination was used to determine if distribution of the mallomonadacean assemblages corresponded with major environmental gradients. Correlations between the first RA axis scores and lakewater pH (r2 = 0.63) and related factors (log10 alkalinity, r2 = 0.66; pCa, r2 = 0.39; pMg, r2 = 0.43) were strongest. Relationships were weaker with average depth, summer epilimnion temperature, elevation, NO3, and total Al, and were not statistically significant with conductivity, color, Secchi disc transparency, total P, chlorophyll a, SO4, and Si. Cluster analysis grouped both lakes and taxa into categories best explained by their pH-related characteristics. Analysis of surficial sediment from lakes with known limnological characteristics is a useful approach for the study of the ecology and taxonomy of the Mallomonadaceae. Our data demonstrate that mallomonadacean distributions reflect lake conditions and, therefore, are potentially useful indicators in limnological and paleolimnological studies.