Whether knowledge of landrace identification is shared among farmers in rural societies is a matter of debate in crop diversity research, and the influence of culture on knowledge heterogeneity remains largely misunderstood. This study analyzes the heterogeneity of farmers' knowledge of crop landrace identification, and investigates factors involved in its patterns. It especially explores the effect of cultural differences by comparing how three ethnolinguistic groups identify and name sorghum diversity in the Mount Kenya region. A set of 293 panicles representing sorghum diversity in the study area was presented for identification to 96 farmers randomly selected in the three groups. A subset of 287 panicles was scored for morphological characteristics using 16 qualitative descriptors, and neutral genetic diversity of 170 of them was described using 18 SSR genetic markers. Distance-based analyses were applied to analyze knowledge patterns within and between groups and to describe the structure of sorghum morphological and genetic diversity. Results show that the degree of heterogeneity of knowledge among farmers varies strongly according to both their ethnolinguistic membership and panicle characteristics, despite their high geographic proximity. The effect of farmers' experience of landraces and of pathways for social learning on inter-individual variations of knowledge is discussed.