Lysimachia iniki is a woody shrub with pendulous branches ranging from 30–150 cm long. The stems are green and densely hirsute, branching above. The leaves are simple and alternate, positioned 2–5(10) mm apart. The leaf blades are obovate to orbicular, cupped upward, and coriaceous, measuring (35)37–45(54) mm long and (25)35–38(42) mm wide when dry. The apex of the leaves is rounded near the top and abruptly acuminate, while the base is cordate. The surfaces are light green and translucent viscid-hirtellous, eventually becoming glabrate. The margins are entire, and the secondary and tertiary veins are prominent and pellucid (translucent). It produces solitary flowers in leaf axils, which are bisexual, 6–7-merous, and funneliform. The pedicels are 15–25 mm long, erect, green, and densely viscid-hirtellous. The calyx comprises 5 sepals with green lobes and hyaline margins and is densely translucent viscid-hirtellous. The corolla lobes are distinct, with the upper 5–7 mm white, the lower portion dark red, and the inner surface densely glandular-punctate. The fruit is a globose capsule, 6–7 mm long, containing dark brown, irregularly shaped seeds that are 1.0-1.1 mm long. It is known to grow in wet, mossy, or rocky cliffs, particularly in the headwaters of the north fork of the Wailua River, at an elevation of approximately 720 meters.