Melaleuca

Shrubs or trees, glabrescent, hairs simple. Leaves usually alternate or opposite [ternate], sometimes decussate; blade venation pinnate to longitudinal. Inflorescences 4–80-flowered, pseudoterminal or axillary, usually spikes or clusters, sometimes flowers solitary (monad). Flowers usually 5-merous, sessile, in triplets (triads) or solitary (monads); hypanthium subglobose to subcylindrical, adnate to ovary proximally or to 3/4 length of ovary; calyx lobes distinct, (0 or) 5; petals white; stamens 25–365, longer than perianth; filaments connate proximally into 5 bundles or, sometimes, distinct and not in bundles; ovary 3-locular; placenta peltate, axile-median to axile-basal; ovules 50–300 per locule. Fruits capsules, green, brown, or gray, subglobose to short-cylindrical, in spikes or clusters, a woody or subwoody hypanthium enclosing a capsule. Seeds 20+, usually obovoid-oblong to obovoid, not winged, with thin testa; cotyledons not or scarcely foliaceous, face-to-face, plano-convex or obvolute, wrapped around each other. x = 11.

Distribution

Introduced; Asia (Malesia), Pacific Islands (Lord Howe Island, New Caledonia), Australia, introduced also widely.

Discussion

Species ca. 300 (4 in the flora).

Melaleuca and Callistemon traditionally have been regarded as separate genera, distinguished by features of the androecium. The staminal filaments are usually distinct in Callistemon with the stamens arranged uniformly around the hypanthium rim. In some species of Callistemon, the stamens are connate towards the base and aggregated in five more or less distinct bundles. This condition is nearly universal in Melaleuca. In view of the similarities between the two genera in many features of the leaves, inflorescences, and fruits, they have been combined under Melaleuca (L. A. Craven 2006). Gill. K. Brown et al. (2001), in an analysis of 5S and ITS-1 rDNA data, found that Callistemon nested within Melaleuca, and a similar result was obtained by R. D. Edwards et al. (2010) on the basis of ndhF data.

Some species of Melaleuca are ornamental (notably M. citrina and M. viminalis) and are widely cultivated. Some of the taller paperbark species have potential for forestry use. Essential oils are produced commercially in Australia, Indonesia, Madagascar, and New Caledonia from some species, mainly the tea tree, M. alternifolia (Maiden & Betche) Cheel, cajuput, M. cajuputi Powell, tea tree or snow-in-summer, M. linariifolia, and punk tree, broad-leaved paperbark, or niauoli, M. quinquenervia (I. Southwell and R. Lowe 1999).

Melaleuca occurs in North America mostly as cultigens but one species, Melaleuca quinquenervia, has become a significant woody weed in Florida.

Selected References

None.

Lower Taxa

Melaleuca citrina, Melaleuca linariifolia, Melaleuca quinquenervia, Melaleuca viminalis

Key

1	Leaves opposite (decussate); flowers in monads.	Melaleuca linariifolia
1	Leaves alternate; flowers in monads or triads.	> 2
2	Flowers joined to inflorescence axes in clusters of 3 (triads), filaments white, cream, greenish white, green, creamy white, or creamy yellow.	Melaleuca quinquenervia
2	Flowers joined to inflorescence axes one-by-one (monads), filaments red, crimson, or mauve.	> 3
3	Filaments distinct.	Melaleuca citrina
3	Filaments connate proximally, usually in 5 bundles (these obscure when bundle claws are short).	Melaleuca viminalis