Vigna subterranea (commonly known as bambara groundnut) is a neglected and underutilized crop, predominantly cultivated by women on small plots in West Africa. Despite its importance in rural areas, no improved varieties are available in the Sahel countries. Although used for both its edible grains and as forage by rural farmers, very few studies have focused on the forage potential of this species. This study aims to assess the genetic variability and heritability of biomass production traits in eight morphotypes of Vigna subterranea collected from southern Niger. The traits studied include plant height (PH), number of leaves (NL), number of branches (NB), and fresh biomass weight (FBW). The experiment was conducted using a randomized complete block design with three replications. The Kruskal-Wallis test revealed a significant difference between the morphotypes only for fresh biomass weight (P = 0.002). However, substantial variability was observed for all traits studied. The phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (CVG) were particularly high for FBW (PCV = 79.78%, CVG = 64.4%) and low for PH (PCV = 13.07%, CVG = 5.99%). Broad-sense heritability ranged from 21% for PH to 65% for FBW, while genetic gain ranged from 1.36 for PH to 52.12 for FBW. These results indicate significant potential for the genetic improvement of these traits, which could enhance biomass productivity and resilience of Vigna subterranea. The implications of these findings for breeding programs are discussed.