The opposite and decussate arrangement of the Lysimachia arvensis var. caerulea leaves expose long internodes between leaf-pairs apart from near the stem-tips. The stem is square in cross-section to slightly winged.

The flowers emerge solitary on longish pedicels from leaf axils. The five stamens arise from the corolla tube and the anthers are exserted. The ovary is superior, the style cylindrical and the tiny stigma three-lobed (Leistner, (Ed.), 2000; Pooley, 1998; iNaturalist).