Lysimachia remyi is an erect, usually many-branched shrub standing 50–200 cm tall, though sometimes it presents as a sprawling, few-branched shrub. The stems, several from the base and ranging from 30–60 cm in length, display a reddish-brown, striate bark. Young shoots are typically rusty pilose to tomentose but tend to become glabrate quickly. The leaves are simple, alternating to subopposite or subternate, and can be closely spaced and imbricate or sometimes well-spaced in fewer-branched plants. The blade shapes vary, being linear-filiform, oblong-linear, linear-elliptic, or narrowly elliptic, often somewhat falcate, with some occasionally reaching up to 15 mm wide and typically measuring 15–55 mm long by 1–8 mm wide. Leaf apex is acute to bluntly acute or attenuate-acute and usually slightly hooked, while the base is attenuate or narrowly cuneate. Initially sparsely pilose, the leaf surfaces generally become glabrate as they mature. The margins are revolute, and the leaves are primarily one-veined, although sometimes lateral veins are evident. Petioles range from (1–)3–8 mm in length, with those on the main stem reaching up to 1.5 cm. Stipules are absent. The flowers are solitarily in the axils of the leaves. These flowers are bisexual (perfect) and actinomorphic (radially symmetric), typically (5)6–8-merous, with pedicels (4–)15–35 mm long that sometimes extend to 20–36 mm in fruit, and are ± rusty pilose, particularly when young. The calyx consists of 5 sepals with lanceolate to ovate or broadly ovate lobes measuring 4–6 mm long. The corolla is reddish-purple to burgundy with darker veins and campanulate, measuring 9–11 mm in length with obovate to narrowly obovate lobes that are imbricate. The stamens are as numerous as and opposite the corolla lobes, with filaments connate up to half their length from the base and adnate to the corolla tube. The anthers are dithecal. The ovary is superior and 1-celled with free-central placentation; the style is singular. The fruit is a broadly ovoid to subglobose capsule measuring 5–8 mm long and regularly dehiscent. Seeds are numerous, nearly black, irregularly shaped, and 1.5–1.9 mm long, with slightly winged margins and a crustaceous seed coat. It inhabits open sites, often on wet cliffs or rock walls in mesic shrubland, wet forests, and subalpine shrublands between 760-2,200 meters.