M. cinerea grows in trees and shrubs up to 23.3 feet (7.1 m) tall, with new growth being densely dull, and grayish to yellowish brown puberulent, with its branchlets becoming glabrate over time. Leaf blades are elliptic or narrowly ovate, with maximum dimension of 6 inches (15 cm) in length and 2.8 inches (7.1 cm) wide. Petioles are 15–33 mm in length, and stipules are absent. The calyx consists of 4 ovate sepals measuring 2.5–3 mm long, characterised as densely grayish puberulent and imbricate. The corolla has 4 valvate, deltate petals 3.5–5 mm long, which are densely puberulent externally. 8 stamens are available in 2 distinct reduced whorls, but always present in functionally pistillate flowers. The ovary is superior, glabrous, and 4-celled and 4-lobed. Its fruit are dark green, measuring 20–30 mm wide, with distinct follicles 11–15 mm long. One or two seeds can be found per cell, characterised as glossy black when ripe, and ovoid-shaped, but sometimes angled due to compression.[6] The original specimen by Gray was described as having glabrous branches with strong approximate leaf-scars, with opposite petioled leaves.[4]
M. cinerea is endemic in Oahu,[3] and thrives in mesic forests within the altitude of 790–2,690 feet (240–820 m).[6]
