Myrsine lanaiensis is a small tree that typically grows to heights of 3 to 6 meters. The branches of these trees are dark purplish-brown when young, featuring conspicuous lenticels and a glabrous texture. The leaves are simple, alternate, and tend to cluster towards the tips of the branches. Leaf blades are elliptic to elliptic-lanceolate or oblong-ovate, measuring 6 to 18 cm in length and 2.3 to 6 cm in width, with an obtuse to rounded apex and a cuneate base. The surfaces of the leaves are generally glabrous, though the lower surfaces can occasionally exhibit short, brown, hirtellous hairs. Young leaves are notably bright red or often feature purple midribs, with a texture ranging from membranous to chartaceous or occasionally coriaceous. The flowers are arranged in bracteolate fascicles of 2 to 12, emerging on short, often stout, woody knobs typically below the leaves, with glabrous pedicels. The flowers are bisexual (perfect), featuring a calyx with 4 to 6 deeply cut lobes and oblong-oblanceolate petals 3 to 4.5 mm long, adorned with conspicuous secretory lines. The ovary is superior and glabrous, leading to dark purple, depressed-globose drupes (fruit) that are approximately 6 to 8 mm in diameter. The seeds 1 per fruit; small, dark-colored, subglobose; excavated at the base. It is native to dry and occasionally mesic forests, often found in open lava fields between 300-1,000 (up to 2,290) meters.