Lysimachia maxima is a sprawling shrub with reddish-brown bark. The leaves are simple and whorled (3 per node) and have an abruptly acuminate apex, a cuneate and sessile base, and weakly revolute margins. The upper surfaces of the leaves display a few scattered hairs when young, which soon become glabrate, while the lower surfaces are sparsely rusty pilose, at least initially. The blades are elliptic-obovate, obovate, or oblanceolate, 38-80 mm long by 18-50 mm wide, thin yet coriaceous, with prominent secondary and tertiary veins. The red-based petioles are relatively short, ranging from (1)2-3(5) mm long, and the plant does not have stipules. The flowers are solitary in leaf axils, perfect, actinomorphic (radially symmetric), and typically 6–7-merous, with pedicels measuring 20–35 mm long and covered in rusty pilose. The calyx consists of 5 sepals with narrowly lanceolate lobes. The corolla is presumed to be purple, campanulate, approximately 10–12 mm long, with obovate, imbricate lobes. The stamens are as many and opposite the corolla lobes, with filaments at the base and dithecal anthers. The superior ovary of the plant is 1-celled, with free-central ovule placentation and a single style. It occurs in montane wet forests at approximately 975 meters.