J.R.Forster & G.Forster
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 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 to not 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 Laurie Johnson published a classification of the family Myrtaceae in the Journal of the Journal 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 published a complete revision of the genus, although it has not been universally accepted, and about ninety species are now recognised.
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 L. riparium growing in Tasmanian rainforest on the edges of rivers. Leptospermum amboinense extends from Queensland to Southeast Asia and three species, L. javanicum, L. parviflorum and 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, Tasmania and New Zealand, where it is one of the most widespread and important native shrub species.
The nectar from the flowers is harvested by bees; this is used to make Leptospermum honey. Honey produced from Australian Leptospermum polygalifolium, also known as jelly bush or the lemon-scented tea tree, has been found to contain up to 1750 mg/kg of 'methylglyoxal' (MGO), an antibacterial compound. However, after neutralization of this compound, the "manuka" honey retains bactericidal activity. Methylglyoxal thus does not appear to be the main contributor to the antimicrobial and antibacterial activities.
In Australia, Leptospermum species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus, including A. lewinii and A. ligniveren. These burrow horizontally into the trunk then vertically down.
Most Leptospermum species make desirable garden plants. The hardiest species (L. lanigerum, L. liversidgei, L. polygalifolium, L. rupestre, L. scoparium) are hardy to about −8 °C (18 °F) to −10 °C (14 °F); others are sensitive to frost. They tolerate most soils, but many supplies specify 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.
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 poolgalifolium) 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.
The following is a list of species accepted by Royal Botanic Gardens, Kew as at February 2017:
- Leptospermum anfractum - Qld
- Leptospermum arachnoides - Qld NSW
- Leptospermum argenteum - NSW
- Leptospermum barneyense - Qld
- Leptospermum benwellii - NSW
- Leptospermum blakelyi - NSW
- Leptospermum brachyandrum - Qld NSW
- Leptospermum brevipes - Qld NSW Vic
- Leptospermum confertum - WA
- Leptospermum continentale - NSW Vic SA
- Leptospermum coriaceum - NSW Vic SA
- Leptospermum crassifolium - NSW
- Leptospermum deanei - NSW
- Leptospermum deuense - NSW
- Leptospermum divaricatum - NSW
- Leptospermum emarginatum - NSW Vic
- Leptospermum epacridoideum - NSW
- Leptospermum erubescens - WA
- Leptospermum exsertum - WA
- Leptospermum fastigiatum - WA SA
- Leptospermum glabrescens - East Gippsland
- Leptospermum glaucescens - Tas
- Leptospermum grandiflorum - Tas
- Leptospermum grandifolium - NSW Vic
- Leptospermum gregarium - Qld NSW
- Leptospermum incanum - WA
- Leptospermum inelegans - WA
- Leptospermum javanicum - Myanmar, Thailand, Malaysia, Indonesia, Philippines
- Leptospermum jingera - Vic
- Leptospermum juniperinum - Qld NSW
- Leptospermum laevigatum - NSW Vic SA Tas
- Leptospermum lamellatum - Qld
- Leptospermum lanigerum - Qld NSW Vic SA Tas
- Leptospermum liversidgei - Qld NSW
- Leptospermum luehmannii - Qld
- Leptospermum macgillivrayi - WA
- Leptospermum macrocarpum - NSW
- Leptospermum madidum - Qld WA NT
- Leptospermum maxwellii - WA
- Leptospermum microcarpum - Qld NSW
- Leptospermum micromyrtus - NSW Vic
- Leptospermum minutifolium - Qld NSW
- Leptospermum morrisonii - NSW
- Leptospermum multicaule - NSW Vic
- Leptospermum myrsinoides - NSW Vic SA
- Leptospermum myrtifolium - NSW Vic
- Leptospermum namadgiensis - NSW
- Leptospermum neglectum - Qld
- Leptospermum nitens - WA
- Leptospermum nitidum - Tas
- Leptospermum novae-angliae - Qld NSW
- Leptospermum obovatum - NSW Vic
- Leptospermum oligandrum - WA
- Leptospermum oreophilum - Qld
- Leptospermum pallidum - Qld
- Leptospermum parviflorum - NG Qld WA NT
- Leptospermum parvifolium - NSW
- Leptospermum petersonii - Qld NSW
- Leptospermum petraeum - NSW
- Leptospermum polyanthum - NSW
- Leptospermum polygalifolium - Qld NSW LHI
- Leptospermum purpurascens - Qld
- Leptospermum recurvum - Sabah, Sulawesi
- Leptospermum riparium - Tas
- Leptospermum roei - WA
- Leptospermum rotundifolium - NSW
- Leptospermum rupestre - Tas
- Leptospermum rupicola - NSW
- Leptospermum scoparium - Vic NSW Tas New Zealand (North + South + Chatham Is)
- Leptospermum sejunctum - NSW
- Leptospermum semibaccatum - Qld NSW
- Leptospermum sericatum - Qld
- Leptospermum sericeum - WA
- Leptospermum speciosum - Qld NSW
- Leptospermum spectabile - NSW
- Leptospermum sphaerocarpum - NSW
- Leptospermum spinescens - WA
- Leptospermum squarrosum - NSW
- Leptospermum subglabratum - NSW
- Leptospermum subtenue - WA
- Leptospermum thompsonii - NSW
- Leptospermum trinervium - Qld NSW Vic
- Leptospermum turbinatum - Vic
- Leptospermum variabile - Qld NSW
- Leptospermum venustum - Qld
- Leptospermum whitei - Qld NSW
- Leptospermum wooroonooran - Qld
- Kew World Checklist of Selected Plant Families
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- Sunset Western Garden Book, 1995:606–607
- Wrigley, John W.; Fagg, Murray (1993). Bottlebrushes, paperbarks & tea trees, and all other plants in the Leptospermum alliance (1181–183 ed.). Pymble, N.S.W.: Angus & Robertson. ISBN 978-0207168673.
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- Stephens, Jonathan M.C.; Molan, Peter C.; Clarkson, Bruce D. (January 2005). "A review of Leptospermum scoparium (Myrtaceae) in New Zealand". New Zealand Journal of Botany. 43 (2): 431–449. doi:10.1080/0028825X.2005.9512966.
- Native honey a sweet antibacterial Archived 2011-03-06 at the Wayback Machine, Australian Geographic, March 3, 2011.
- Kwakman PHS; te Velde AA; de Boer L; Vandenbroucke-Grauls CMJE; Zaat SAJ (2011). "Two major medicinal honeys have different mechanisms of bactericidal activity". PLoS ONE. 6 (3): e17709. doi:10.1371/journal.pone.0017709. PMC 3048876. PMID 21394213.
- Molan, P. (2008). "An explanation of why the MGO level in manuka honey does not show the antibacterial activity". New Zealand BeeKeeper. 16 (4): 11–13.
- Media related to Leptospermum at Wikimedia Commons