The genus Frustulia was found to be an abundant and important component of the attached algal community in a suite of dilute, poorly buffered, and acidic ponds situated in the Ocala National Forest in north-central Florida. Six species were found in the study, including Frustulia krammeri Lange-Bertalot & Metzeltin, Frustulia saxonica Raben horst, Frustulia crassinervia (Brébisson) Lange-Bertalot & Krammer, Frustulia pseudomagaliesmontana Camburn & Charles, Frustulia bahlsii Edlund & Brant, and a newly described taxon, Frustulia trochus Siver & Baskette sp. nov. In addition, an emended description is provided for F. pseudomagaliesmontana. Each species was studied in detail with both light and scanning electron microscopy, and the importance of specific morphological characters was also examined with principal components analysis. In addition to valve shape and size, striae density and areolae density, the structure of the helictoglossae, raphe fissures, and areolae were all found to be useful and important characters in distinguishing among species. Three distinct types of helictoglossae, referred to as linear, rolled tongue, and hoop shaped, are discussed. Taxa with linear or rolled-tongue-shaped helictoglossae also had T-shaped raphe fissures and circular hymen coverings. Taxa with hoop-shaped helictoglossae had teardrop-shaped raphe fissures and rectangular hymen coverings. K-cluster analysis was used to examine the distinction between F. krammeri and F. saxonica relative to the historical separation of F. rhomboides from F. saxonica.Key words: acidic ponds, Florida, Frustulia, Frustulia trochus, new species, Ocala National Forest.