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During the course of the study of Pteridophyta for the Flora of the Province of San Juan, Argentina, directed by R. Kiesling, several taxonomic novelties have appeared, among them, a new species of Cheilanthes. In order to find the taxonomic position of this species, related species were examined. These species had not been grouped by Tryon and Tryon (1982, pp. 251-255) in their informal classification of species groups in Cheilanthes. Because their characters did not allow inclusion in any of these groups, a new group is proposed. The systematics of the cheilanthoid ferns is being studied by many authors using cytological and electrophoretical data, in order to find more coherent classifications of these complex taxa (Vida et al., 1983; Gastony & Windham, 1987; Wollenweber, 1985; Windham, 1986,1987; Benham et al., 1988). Recently, Argyrochosma and Astrolepis were separated from Notholaena (Windham, 1987; Benham et al., 1988). However, a modern taxonomic treatment is still necessary in Cheilanthes. In fact, this large genus has recently been extended by additions of species formerly placed in Adiantopsis, Doryopteris, and Notholaena (Tryon & Tryon 1982, pp. 267, 272, 296). MATERIALS AND METHODS Collections in BA, BAB, BAF, GH, HBR, ICN, LP, MBM, PACA, and SI and type specimens at K, P, SI, and W, were studied. Ecological and geographical information was obtained from herbarium labels and field data. The following characters were used to distinguish and group the species: rhizome type; rhizome and basal stipe scales; stipe and rhachis sections; axis color and direction; blade division; venation; stipe, rhachis, and blade indument; sorus position; and spore wall (sculpture and structure). Spores from herbarium material were studied with LM and SEM. For light microscopy, material was acetolized by Erdtman's technique, preceded by treatment with hot sodium carbonate (3%) for 2 minutes, with the aim of not destroying the perispore. Slides for study with LM were mounted in glycerine jelly. An Olympus BH2 microscope was used. For the SEM, material was treated with sodium carbonate, washed and suspended in 96% ethanol, then transferred to acetate plates and later coated with gold. A JEOL JSMT-100 SEM was used.