Simple Summary Sustainable ruminant production increasingly requires alternative forages that combine high nutritional value with a low environmental footprint. The Urtica dioica perennial wild plant is naturally adapted to a wide range of climatic conditions. In this study, Urtica dioica was harvested at the early flowering stage from three bioclimatic zones in Tunisia (arid, semi-arid, and sub-humid) and analyzed for nutritional value and greenhouse gas emissions. Across all ecotypes, Urtica dioica consistently provided high and stable protein levels. The arid-zone plants contained more structural fiber, polyphenols, and lipids, which reduced digestibility, fermentation efficiency, and metabolizable energy yield, but significantly lowered methane emissions per unit of dry matter, degraded dry matter, and total gas. Semi-arid ecotypes offered a similar nutritional value to sub-humid plants while limiting methane production per unit of dry matter, degraded dry matter, and total gas, representing a balance between productivity and environmental sustainability. These findings demonstrate that both the nutritional quality and enteric methane emissions of Urtica dioica are strongly shaped by its bioclimatic origin, with semi-arid ecotypes showing particular promise as climate-resilient, eco-friendly feed resources for ruminant production systems.Abstract Climate change, feed shortages, and rising production costs highlight the need for alternative and sustainable forages for ruminants. This study aimed to evaluate the nutritional composition, in vitro ruminal fermentation, and methane emissions of Urtica dioica ecotypes originating from contrasting bioclimatic zones in Tunisia. Aerial parts of Urtica dioica were harvested at the early flowering stage from arid, semi-arid, and sub-humid regions. Samples were subjected to chemical composition in vitro ruminal fermentation to determine dry matter degradability (DMD), neutral detergent fiber degradability (NDFD), metabolizable energy (ME), and methane production. The results demonstrate that Urtica dioica is a promising protein-rich forage, with a stable crude protein content across ecotypes (18.58-20.97% of dry matter). In contrast, NDFD, DMD, ME, and methane emissions varied significantly according to origin. The arid ecotype, characterized by the highest fiber, ether extract, and polyphenol content, exhibited the lowest DMD (53% vs. 61% and 60%), NDFD (45% vs. 55% and 56%), and ME (7.2 vs. 8.6 and 9.0 MJ/kg dry matter) but produced the lowest methane emissions (38.8 vs. 53.2 and 74.2 mL CH4/kg DMD) compared with the semi-arid and sub-humid ecotypes. The semi-arid and sub-humid ecotypes had comparable DMD, NDFD, and ME values; however, methane emissions were higher in the sub-humid ecotype. Overall, the semi-arid ecotype provided the most favorable balance between nutritive quality and environmental sustainability. These findings highlight the critical role of ecological origin in determining the feeding value and greenhouse gas footprint of Urtica dioica, providing a scientific basis for its potential use as a sustainable forage in ruminant feeding systems.