Sweet corn (Zea mays L.) has high levels of sugar in the endosperm, being used for self-consumption by families in the far west of the state of Santa Catarina (FWSC), southern Brazil. The present work aimed to identify the genes responsible for the sweet phenotype and to characterize morphologically nine local corn varieties conserved in this region. The allelic tests proved the presence of two known recessive alleles (sugary1 mutant/sweet and shrunken2 mutant/super sweet) in eight of the nine varieties studied, and a third gene of unidentified genetic origin. The morphological characterization of ear and grain showed a similarity between the varieties for qualitative characters and a greater variation between and within the varieties for quantitative characters. The cluster analysis divided the materials into four groups and one isolated variety whose gene encoding the sweet phenotype can be a rare gene or still unknown. The results point to the possibility of a new allele having been selected under the specific conditions of the FWSC region, which presents environmental and social factors that influence the diversification of the Zea genus. The continuation of genetic studies on the sweet phenotype of this variety and the development of integrated strategies of in situ on farm and ex situ conservation and participatory breeding in FWSC can contribute to the expansion of the genetic variability of sweet corn and encourage conservation and use of this local germplasm.