The new species Gymnocalycium campestre Řepka is validated from Córdoba, Argentina, and is affiliated with the G. erinaceum J. G. Lamb. group of Gymnocalycium Pfeiff. ex Mittler subg. Gymnocalycium (Cactaceae, Trichocereeae). The new taxon is compared with several sympatric close relatives or similar taxa. Distinctive characters of the new species include the gray-green plant body with frequently bronze-colored epidermis, distinct tubercles under the areola, the radially arranged, whitish (often chalky) marginal spines (mostly seven) with the longer portion of the spine with colored base, further considerably long and whitish to pale pinkish or pinkish colored flowers, with perianth often 1 to 1.5 times longer than the pericarpel. Flowering time is intermediate in relation to that of other taxa of the group (end of spring, December in Argentina). The seeds are small (1.197 ± 0.048 mm long) within the group. The new species significantly differs in genome size and ploidy level (tetraploid) from other taxa of the G. erinaceum group (diploids). The new taxon has been found in 27 populations, which documents a distributional area separate from that of other related taxa, with the exception of G. erinaceum. Based on the morphological, cytological, and geographical features, the authors hypothesize that the new species may have a hybridogenous origin, formed by hybridization and introgression from ancestors that occur in its geographic vicinity.