''Leptospermum'' is a genus of shrubs and small trees in the myrtle Family (biology), family Myrtaceae commonly known as tea trees, although this name is sometimes also used for some species of ''Melaleuca''. Most species are endemism, endemic to Australia, with the greatest diversity in the south of the continent, but some are Indigenous (ecology), native to other parts of the world, including New Zealand and Southeast Asia. Leptospermums all have five conspicuous petals and five groups of stamens which alternate with the petals. There is a single Stigma (botany)#Style, style in the centre of the flower and the fruit is a woody Capsule (botany), capsule. The first formal description of a leptospermum was published in 1776 by the Germans, German botanists Johann Reinhold Forster and his son Johann Georg Adam Forster, but an unambiguous definition of individual species in the genus was not achieved until 1979. Leptospermums grow in a wide range of habitats but are most commonly found in moist, low-nutrient soils. They have important uses in horticulture, in the production of honey and in floristry.

Description

Plants in the genus ''Leptospermum'' range in size from prostrate shrubs to small trees, and have fibrous, flaky or papery bark. The leaves are arranged alternately and are relatively small, rigid and often aromatic when crushed. The flowers may be solitary or in groups, and have Bract#Bracteole, bracteoles and sepals which in most species fall off as the flower opens. There are five spreading, conspicuous petals which are white, pink or red. There are many stamens which are usually shorter than the petals and in five groups opposite the stamens, although they often appear not to be grouped. A simple style usually arises from a small depression in the ovary which has from three to five sections in most species, each section containing a few to many ovules. The fruit is a woody capsule which opens at the top to release the seeds, although in some species this does not occur until the plant, or the part of it, dies.

Taxonomy and naming

The first formal description of a leptospermum was published by Johann Reinhold Forster and Johann Georg Adam Forster in their 1776 book, ''Characteres Generum Plantarum''. In 1876, George Bentham described twenty species, but noted the difficulty of discriminating between species. ("The species are very difficult to discriminate.") Of the species he named, only ten remain as valid. In 1979, Barbara Briggs and Lawrence Alexander Sidney Johnson, Laurie Johnson published a classification of the family Myrtaceae in the ''Proceedings of the Linnean Society of New South Wales''. Although there have been revisions to their groupings, their paper allowed a systematic examination of species in the genus ''Leptospermum''. In 1989, Joy Thompson (botanist), Joy Thompson published a complete revision of the genus. In 2000, O'Brien ''et al.'' published yet another revision, using Maturase K, matK-based evidence to suggest that ''Leptospermum'' is Polyphyly, polyphyletic, and should be split into persistent, Western non-persistent, and Eastern non-persistent fruiting plants, with ''Leptospermum spinescens'' as an outlier. However, neither phylogeny has been universally accepted. Current estimates recognize about ninety species of ''Leptospermum''. The common name ''tea tree'' derives from the practice of early Australian settlers who soaked the leaves of several species in boiling water to make a herbal tea. The genus name (''Leptospermum'') means "slender-seeded".

Distribution and habitat

Most ''Leptospermum'' species are endemic to Australia where most are found in southern areas of the country. They are most common in moist, nutrient-poor soils although they sometimes occupy other situations. ''Leptospermum laevigatum'' is usually found growing on beach sand and ''Leptospermum riparium, L. riparium'' growing in Tasmanian rainforest on the edges of rivers. ''Leptospermum amboinense'' extends from Queensland to Southeast Asia and three species, ''Leptospermum javanicum, L. javanicum'', ''Leptospermum parviflorum, L. parviflorum'' and ''Leptospermum recurvum, L. recurvum'' are endemic to southeast Asia. ''L. recurvum'' is only found on Mount Kinabalu in Sabah. ''Leptospermum scoparium'' is one of the most widespread in the genus and occurs in New South Wales, Victoria, Australia, Victoria, Tasmania and New Zealand, where it is one of the most widespread and important native shrub species.

Ecology

In Australia, ''Leptospermum'' species are sometimes used as food plants by the larvae of Hepialidae, hepialid moths of the genus ''Aenetus'', including ''A. lewinii'' and ''A. ligniveren''. These burrow horizontally into the trunk then vertically down.

Uses

Use in horticulture

Most ''Leptospermum'' species make desirable garden plants. The hardiest species (''L. lanigerum, L. liversidgei, L. polygalifolium, L. rupestre, L. scoparium'') are hardy to about to ; others are sensitive to frost. They tolerate most soils, but many suppliers specify ericaceous bed, ericaceous (i.e. lime-free) compost with good drainage and full sun. Established plants are drought tolerant. They are often found as hedge plants on the west coast of the United States, and some species are popular for cultivation as bonsai. Many cultivars exist.

Use in floristry

These flowers are also grown in double cultivars and are used in floral designs. However, they do not last when out of water and the single flowers do not last when wired. The 'Pacific Beauty' (''Leptospermum polygalifolium'') is a useful flower to use in large church-service bowls and function arrangements, however use of ''Leptospermum'' in corporate designs is less desirable as they dry and drop when subjected to heating and air conditioning.

Honey production

The nectar from the flowers is harvested by bees, yielding Leptospermum honey, which is marketed as Manuka honey. Honey produced from Australian ''Leptospermum polygalifolium'' is also known as ''jelly bush'' or the ''lemon-scented tea tree''.Native honey a sweet antibacterial
''Australian Geographic'', March 3, 2011.

Species

The following is a list of species accepted by Plants of the World Online as at August 2024: *''Leptospermum amboinense'' Carl Ludwig Blume, Blume - Qld, Malesia *''Leptospermum arachnoides'' Joseph Gaertner, Gaertn. spidery tea-tree - Qld, NSW *''Leptospermum argenteum'' Joy Thompson, Joy Thomps. Mt Royal tea-tree - NSW *''Leptospermum barneyense'' A.R.Bean - Qld *''Leptospermum continentale'' Joy Thomps. prickly tea-tree - NSW, Vic, SA *''Leptospermum crassifolium'' Joy Thomps. - NSW *''Leptospermum deuense'' Joy Thomps. - NSW *''Leptospermum emarginatum'' H.L.Wendl. ex Johann Heinrich Friedrich Link, Link - NSW, Vic *''Leptospermum epacridoideum'' Cheel - NSW *''Leptospermum glabrescens'' N.A.Wakef. - Vic *''Leptospermum grandiflorum'' Joachim Conrad Loddiges, Lodd. George Loddiges, G.Lodd. & W. Loddiges, W.Lodd. - Tas *''Leptospermum grandifolium'' Sm. - NSW, Vic *''Leptospermum gregarium'' Joy Thomps. - Qld, NSW *''Leptospermum hoipolloi'' Luzie M.H. Schmid, L.M.H.Schmid & Peter James de Lange, de Lange - New Zealand *''Leptospermum javanicum'' Blume - Myanmar, Thailand, Malaysia, Indonesia, Philippines *''Leptospermum juniperinum'' Sm. - Qld, NSW *''Leptospermum lanigerum'' (Daniel Solander, Sol. ex William Aiton, Aiton) Sm. - Qld, NSW, Vic, SA, Tas *''Leptospermum liversidgei'' R.T.Baker & H.G.Sm. - Qld, NSW *''Leptospermum macrocarpum'' (Joseph Maiden, Maiden & Ernst Betche, Betche) Joy Thomps. - NSW *''Leptospermum micromyrtus'' Miq. - NSW, Vic *''Leptospermum minutifolium'' C.T.White - Qld, NSW *''Leptospermum morrisonii'' Joy Thomps. - NSW *''Leptospermum myrtifolium'' Franz Sieber, Sieber ex DC. - NSW, ACT, Vic *''Leptospermum nitidum'' Hook.f. - Tas *''Leptospermum novae-angliae'' Joy Thomps. - Qld, NSW *''Leptospermum obovatum'' Robert Sweet (botanist), Sweet - NSW, Vic *''Leptospermum oreophilum'' Joy Thomps. - Qld *''Leptospermum parvifolium'' Sm. - Qld, NSW *''Leptospermum petersonii'' F.M.Bailey - Qld, NSW *''Leptospermum petraeum'' Joy Thomps. - NSW *''Leptospermum polygalifolium'' Salisb. - Qld, NSW, Lord Howe Island ** Leptospermum polygalifolium subsp. cismontanum, ''Leptospermum polygalifolium'' subsp. ''cismontanum'' Joy Thomps. - Qld, NSW ** Leptospermum polygalifolium subsp. howense, ''Leptospermum polygalifolium'' subsp. ''howense'' Joy Thomps. - Lord Howe Island ** Leptospermum polygalifolium subsp. montanum, ''Leptospermum polygalifolium'' subsp. ''montanum'' Joy Thomps. ** ''Leptospermum polygalifolium'' Salisb. subsp. ''polygalifolium'' - NSW **''Leptospermum polygalifolium'' subsp. ''transmontanum'' Joy Thomps. - Qld, NSW **''Leptospermum polygalifolium'' subsp. ''tropicum'' Joy Thomps. - Qld *''Leptospermum recurvum'' Hook.f. - Sabah, Sulawesi *''Leptospermum repo'' de Lange & L.M.H.Schmid - New Zealand *''Leptospermum riparium'' Dennis Ivor Morris, D.I.Morris - Tas *''Leptospermum rotundifolium'' (Maiden & Betche) Frederick Arthur Rodway, F.A.Rodway - NSW *''Leptospermum rupestre'' Hook.f. - Tas *''Leptospermum rupicola'' Joy Thomps. - NSW *''Leptospermum scoparium'' J.R.Forst. & G.Forst. - Vic, NSW, Tas, NZ *''Leptospermum sejunctum'' Joy Thomps. - NSW *''Leptospermum spectabile'' Joy Thomps. - NSW *''Leptospermum sphaerocarpum'' Cheel - NSW *''Leptospermum squarrosum'' Joseph Gaertner, Gaertn. - NSW *''Leptospermum tairawhitiense'' Graeme J. Atkins, G.J.Atkins, de Lange & Matthew Anton Martyn Renner, M.A.M.Renner - New Zealand *''Leptospermum thompsonii'' Joy Thomps. - NSW *''Leptospermum turbinatum'' Joy Thomps. - Vic *''Leptospermum variabile'' Joy Thomps. - Qld, NSW *''Leptospermum wooroonooran'' F.M.Bailey - Qld

References

{{Authority control Leptospermum, Myrtaceae genera Taxa named by Georg Forster Taxa named by Johann Reinhold Forster