Euphorbia thymifolia (Euphorbiaceae) is a prostrate herb, distinguished from similar species by the combination of serrate leaf margin, puberulous ovary/fruit with capitate styles and pedicel not accrescent in fruit, splitting the involucre of the cyathia during maturation. In this paper we present the first record of E. thymifolia for the state of Acre, in Alto Juruá region, municipality of Cruzeiro do Sul, in a residential sidewalk crack habitat (07°36′58″S, 072°41′14.12″W WGS84). We also comment on its habitat and distribution, and include comparisons with commonly misidentified related species.