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Figure 1. A substantial 

Melaleuca leucadendra 

on a well-watered site in 

north-western Queensland

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oduction to the genus 




leaves, produces leaves measuring 75–270 mm in length, 

representing some of the longest in the genus. Leaves are 

entire, dorsiventral or isobilateral, usually coriaceous, flat, 

concave, centric or semi-terete, sessile or petiolate. Leaf 

shape is also highly variable, including elliptic, cordate, 

falcate, lanceolate, linear, oblong, ovate, obovate, elliptic or 

triangular. Leaves are cordate, attenuate, cuneate, truncate 

or obtuse at the base. Mature leaf blades may be glabrous, 

pubescent or woolly. They are carried in either alternate, 

opposite, spiral, decussate or occasionally ternate (whorls 

of three leaves) arrangement. Mature leaves are without 

stipules and without a persistent basal meristem. Mela-

leuca leaves are usually obviously oil-gland dotted and 

are aromatic or without marked odour. Leaf venation 

is pinnate, longitudinal or longitudinal-pinnate and is 

frequently obscure.


Flowers are in spikes or clusters, or sometimes solitary; 

the basic floral unit is a monad, dyad or triad; the calyx 

lobes are five or rarely may be fused into a ring of tissue; 

the petals are five; the hypanthium is fused to the ovary in 

the proximal region only, or for up to three-quarters the 

length of the ovary or, rarely, for almost all the length of the 

ovary; the stamens are few to numerous, the filaments are 

fused for part of their length into five bundles and inserted 

on a staminal ring or free and not in bundles wherein the 

filaments are inserted on the hypanthium apex with the 

staminal ring obsolete, the anthers are dorsifixed (or rarely 

basifixed) and versatile, with two parallel cells that open via 

longitudinal slits; the ovary has three locules, the placentae 

are peltate and axile-median to axile-basal, the ovules are 

few to numerous (Figures 3 and 4).

Species vary widely in flower colour, with about half 

of all species having filaments of white through cream to 

yellow or green, while the others have pink, red or mauve 

filaments. In many species, the contrasting yellow anthers 

at the ends of these brightly coloured filaments result in a 

spectacular floral display.

Reproductive biology

Melaleucas generally produce only morphologically 

bisexual (hermaphroditic) flowers but this is not uni-

versal. About 160 species are always hermaphroditic, i.e. 

all inflorescences have only bisexual flowers. Examples 

are M. quinquenervia and M. viminalis. About 90 spe-

cies are always andromonoecious, i.e. there are male and 

hermaphroditic inflorescences on the one plant. Typically, 

the male inflorescences are on the outside of the plant and 

possibly serve as advertisements to potential pollinators, 

while the hermaphroditic inflorescences are within the 

canopy, where they may be somewhat protected from 

predation but are still close enough to the outside of the 

plant to attract a pollinator. Examples of andromonoe-

cious species are M. gibbosa and M. uncinata. About 30 

species include some plants that are hermaphroditic and 

others that are andromonoecious. Examples of this type are 

M. hamulosa and M. incana. One species, M. cornucopiae, 

is particularly interesting as some plants are monoecious 

(with both male and female inflorescences on the same 

plant) and others are gynoecious (with female inflores-

cences only). The above data are based on the study of 

herbarium specimens supplemented with observations 

on living plants (L.A. Craven, unpublished data) and need 

verification with additional field studies. However, some 

general statements can be made about specific groups of 

Figure 2. Bark types in Melaleuca: papery, as in (A) M. exuvia; and rough, as in (B) M. bracteata

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oduction to the genus 




Figure 4. Flower and fruit of Melaleuca linearis, a species with free stamens (drawings by M. Fagg)

Figure 3. Flower and fruit of Melaleuca leucadendra, a species with its stamens in bundles (drawings by M. Fagg)


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oduction to the genus 



interest. It appears that all the species of the broad-leaved 

paperbark group are hermaphroditic, all of the broombush 

group are andromonoecious, and most of the species allied 

to M. alternifolia are hermaphroditic (M. linophylla may 

be hermaphroditic or andromonoecious but this needs 

verification in the field).

Baskorowati et al. (2010a, b, c) describe the reproduc-

tive biology of M. alternifolia (summarised in Figure 5) 

which is an example of floral structure and development 

in a hermaphroditic species.

Timing of flowering

Flowering starts early in many species. For example, 

M. alternifolia planted in breeding populations in northern 

New South Wales set the first flower buds as early as 2 years 

after planting. However, the first ‘reasonable’ flowering 

(defined as 45% of trees) did not occur until almost 4 years 

from plantings within the species’ natural range (Doran 

et al. 2002). In M. alternifolia, a cold winter (minimum 

temperatures below 5 °C) appears to stimulate floral bud 

formation while good spring rains are needed to support 

a good flowering and retention of the developing fruit 

(Baskorowati et al. 2010a, c).

Flowering periodicity and intensity in Melaleuca species 

are highly variable between species and sites. In general, 

most species flower in the late winter – spring – summer 

period, some peak in autumn and winter, and others 

may flower all year round. The natural flowering pattern 

can be disrupted when a species is planted outside its 

normal range. For example, flowering of M. alternifolia 

in its region of natural occurrence is at its peak in spring 

(October–November) but the species flowers in winter 

when planted in Western Australia. The period for the 

morphological development of buds, flowers and fruit 

leading to the development of mature seed also varies 

between Melaleuca species. In M. alternifolia, a period 

of 16–18 months is required (Baskorowati et al. 2010a, c) 

but in summer-flowering tropical species (e.g. M. leuca-

dendra), geared to shed their seed in response to the next 

summer’s monsoonal rainfall, a shorter period of about 12 

months is typical.

Pollination and pollen biology

Melaleucas are mostly insect-pollinated. Hawkeswood 

(1980), for example, showed that jewel beetles (Diadoxus 

spp.) were the main pollinators of M. pauperiflora in 

Western Australia and South Australia. Baskorowati et al. 

(2010a, b) observed a wide variety of insects visiting the 

flowers of M. alternifolia in New South Wales, including 

large flying insects like honey bees (Apis mellifera), flies 

and wasps (Figure 6). These authors also found that small 

insects like thrips (Thrips imaginis and T. tabacci) were 

the dominant visitors to the flowers of M. alternifolia 

and are important pollinators, as confirmed by exclusion 

experiments. Pollination is probably also effected by birds, 

notably lorikeets and honeyeaters, which are often seen 

visiting the flowers of bottlebrushes and broad-leaved 

paperbarks. Fruit bats (family Pteropodidae) also feed on 

flowering broad-leaved paperbarks and may be pollinators 

for these species.

Thornhill et al. (2012) studied the pollen morphology 

of 21 species of Melaleuca (including six species of the 

former genus Callistemon) using scanning electron and 

light microscopy. A general description from this work 

follows, combining methods and descriptions of the two 

relevant genera. Pollen grains were tricolporate (Figure 7), 

except for some pollen of M. citrina (as C. citrinus) which 

was tetracolporate. Pollen had a rugulate exine, except for 

M. nesophila grains that had a granulate/scabrate exine. 

Pollen sides were straight, or less commonly convex or 

concave, and the colpal morphology was consistently para-

syncolpate with angular colpi, except for some grains of 

M. virens (as C. viridiflorus) which had arcuate colpi. Pollen 

ambs were round or pointed, or less commonly notched or 

flat. Colpal edges were smooth or occasionally rough and 

Figure 5. Monthly progress in flowering and fruit 

development in Melaleuca alternifolia (derived 

from Baskorowati 2006)

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oduction to the genus 




Figure 6. Some of the potential insect pollinators of Melaleuca alternifolia: (A) honey bee (Apis mellifera); 

(B) butterfly of family Lycaenidae; (C) butterfly of family Nymphalidae; (D, E) wasps of family Sphecidae; (F) wasp 

of family Vespidae; (G) beetle of family Lycidae; and (H) fly of family Calliphoridae (Source: Baskorowati 2006)










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oduction to the genus 



the apocolpial field was not visible or psilate. Some pollen 

of the former genus Callistemon lacked an apocolpial island 

or had a small irregular polar island, but all other observed 

species possessed closely fitting apocolpial islands. Overall, 

pollen length range was 11.0–29.5 µm and the colpus to 

length ratio range was 26.4–56.8%. Two different pollen 

types were observed in Melaleuca by these authors: those 

with large apocolpial islands, such as in many species of the 

M. leucadendra complex and former Callistemon species; 

and those with medium-size, syncolpate pollen with faint 

granulate patterning. The structure of the Melaleuca pol-

len grain, with its lack of sculpturing and its propensity for 

stickiness and clumping, supports the view that it is mainly 

dispersed by insects or flying vertebrates.

There is limited published information about pollen 

viability in Melaleuca and its longevity under different 

storage conditions. A report on viability of M. cajuputi 

subsp. cajuputi pollen using an agar medium showed 

that pollen was highly viable (66%) soon after collection, 

had 35% viability after 3 months of storage in an airtight 

bottle in the refrigerator (3–5 °C), but this had decreased 

to 4% viability after 4.5 months (Hendrati et al. 2002). 

Baskorowati et al. (2010a, b) found that pollen viability in 

M. alternifolia varied significantly with time (tested at 1, 

14, 26, 39 and 52 weeks) and temperature (21–24 °C, 5 °C 

and –18 °C) of storage. Pollen of this species was still viable 

after 52 weeks of storage at all temperatures, with storage 

at –18 °C giving the best results (22%).

Most is known of the sequence of pollen release and 

stigma receptivity in M. alternifolia following the work of 

Baskorowati et al. (2010a, b, c). Consistent with reports 

on other Melaleuca species (e.g. Barlow and Forrester 

1984), there is only slight dichogamy in individual flow-

ers in M. alternifolia. The male phase, when pollen is first 

shed, occurs 1.5 days post anthesis, while the female phase, 

defined as the period of stigmatic exudate formation, occurs 

3–4 days post anthesis. The synchrony of flowering within 

and between inflorescences on the one tree, the duration of 

flowering and abundant pollen provide ample opportunity 

for geitonogamy in the species. Despite this, M. alternifolia 

displays a breeding system that is preferentially outcross-

ing: Butcher et al. (1992) reported an outcrossing rate of 

93% and Rosseto et al. (1999) 86% for M. alternifolia. Self-

pollination, however, can occur, at least when manipulated. 

J.C. Doran and G.F. Moran (unpublished report, 2002) 

reported a selfing rate of up to 28% among progeny of some 

trees when their flowers were bagged without emascula-

tion. A similar result was reported by Kartikawati (2005) 

for M. cajuputi subsp. cajuputi in a seed orchard in Yogya-

karta, Indonesia, where a few individual trees in the orchard 

proved to be self-compatible, although most were found to 

be self-incompatible. Baskorowati et al. (2010a, b), reported 

that a self-incompatibility system operates in the style and is 

complemented by late-acting, self-incompatibility mecha-

nisms discriminating against self-pollen tubes when they 

descend to the ovary, based on microscopic observation of 

pollen-tube development in M. alternifolia (Figure 8). Bar-

low and Forrester (1984) also studied self-incompatibility 

in various Melaleuca species, although not in M. alternifolia, 

and found that self-pollen tubes do not penetrate past the 

base of the style.


Natural hybridisation in Melaleuca appears to be restricted 

to within groups of closely related species, although there 

has been anecdotal mention of wider crosses occurring 

spontaneously in cultivated melaleucas. Hybridisation 

occurs very widely across the genus and examples noted 

in both the field and the herbarium have been listed by 

Craven (2006). In all, over 20 examples are known. It is 

expected that, as comprehensive DNA studies are under-

taken on species complexes within the genus, more will 

become known as to the extent of past and (relatively) 

recent hybridisation events.

Natural hybridisation between M. alternifolia and 

M. linariifolia has long been suspected in tea tree popu-

lations near Port Macquarie, New South Wales. This 

suspicion has arisen due to the intermediate leaf morphol-

ogy, the occurrence of transgressive oil components in 

leaves of the Port Macquarie population of M. alternifolia, 

similarities in oil composition with M. linariifolia, and 

sympatry with M. linariifolia (Butcher 1994). Butcher et 

al. (1995) were able to confirm the hybrid status of the Port 

Macquarie populations in a study of relationships using 

chloroplast DNA.


The fruit consists of a three-celled capsule within a usually 

woody to subwoody fruiting hypanthium, which is often 

cup-shaped but also frequently is described as globular, 

Figure 7.  Scanning electron micrograph of Mela­

leuca alternifolia pollen (Source: Baskorowati 2006)


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oduction to the genus 



urceolate, spherical, cylindrical, barrel-shaped, or ovoid; 

calyx lobes persist in the fruits of some species and are a 

useful aid to identification. Individual capsules are usu-

ally small and not greater than 0.5 cm long × 0.5 cm in 

diameter, although some are larger. Fruits are subsessile 

to sessile (e.g. see Figure 5), persistent (partial immersion 

in the stem is common in southern Australian species) or 

shedding (fruits of some tropical species ripen and shed 

in rhythm with the wet season). They are dehiscent and 

usually many seeded. Melaleuca alternifolia, for example, 

gave from 26 to 57 viable seeds per capsule in a study 

of variation in this character between individual trees 

(Baskorowati et al. 2010a, c).


The seed has a membranaceous or rarely coriaceous testa 

containing an embryo but no endosperm. It is unwinged 

and small—seeds of 46 largely Western Australian species 

had a mean length of 1 mm with a range of 0.5–2.0 mm 

(Sweedman 2006). Seeds are highly variable in shape and 

in the sculpturing and colour of the seed surface (see scan-

ning electron micrographs in Sweedman 2006).

Typically in melaleucas, as in eucalypts and several 

other genera of the family Myrtaceae, the fine particles 

that dehisce from the fruit are a mixture of viable seed 

and unfertilised ovules/ovulodes commonly referred to 

as ‘chaff’. Because of their similarity in shape, colour and 

small size in many Melaleuca species, it is almost impos-

sible to separate the two by the naked eye and even when 

employing a microscope and other mechanical aids like 

winnowing. For this reason, Melaleuca seed is usually han-

dled as this mixture where the percentage of viable seeds 

to chaff may be less than 10% (Rayamajhi et al. 2002). Ger-

mination rates for most species are given as viable seed per 

unit weight of seed and chaff mixture. For example, 27 Mel-

aleuca species that have each received multiple (2–33 seed 

tests per species) four-replicate seed tests over time at 

the Commonwealth Scientific and Industrial Research 

Organisation’s (CSIRO’s) Australian Tree Seed Centre gave 

an overall average of 3,700 germinants/g of seed and chaff 

mix with a range of 1,600–6,000 germinants/g. The highest 

germination rate on record at the Centre was for a seedlot 

of M. bracteata that gave an average of 17,000 germinants/g 

of seed and chaff mix.


Cotyledons are planoconvex to obvolute and are not or 

scarcely foliaceous.

Geographical distribution 

and ecology

Natural occurrence and ecology

Melaleuca principally is an Australian genus. Eight species, 

two of which are endemic (M. pustulata and M. virens), 

occur in Tasmania; one endemic species, M. howeana, 

occurs on Lord Howe Island in the Tasman Sea; and 

there are seven endemic species in New Caledonia 

(M. brevisepala, M. brongniartii, M. buseana, M.  daw sonii, 

M. gnidioides, M. pancheri and M. sphaerodendra). Several 

species of the Australian monsoon-tropical, broad-leaved 

paperbarks (the M. leucadendra group) also occur in 

adjacent areas of Papua New Guinea; i.e. M. dealbata, 

M. leucadendra, M. nervosa, M. stenostachya, M. viridi-

flora, with M. dealbata and M. viridiflora also in Papua 

Figure 8. Fluorescence micrograph of pollen 

tube growth (stained with decolourised aniline 

blue) in the pistil of Melaleuca alternifolia, 4 days 

after cross-pollination (Source: Baskorowati 

et al. 2010a)

2. I


oduction to the genus 




province in Indonesia and M. leucadendra extending as 

far as the Maluku Islands of Indonesia. Melaleuca aca-

cioides also occurs in southern Papua New Guinea. Two 

species of the M. leucadendra group have a much broader 

distribution: M. quinquenervia extends to Papua province, 

Papua New Guinea and New Caledonia and M. cajuputi 

occurs from northern Australia through Malesia to South-

East Asia. The indigenous western Malesian – South-East 

Asian populations of the latter species are referable to 

M. cajuputi subsp. cumingiana and represent an interest-

ing example of dispersal across Wallacea (Barlow 1988; 

Lum 1994).

Within Australia, the majority of the species and the 

greatest phylogenetic diversity occur in the south-western 

region of Western Australia, especially on the leached 

north-western and central to southern sand plains, and in 

the clay soils in the drier eastern region of the south-west. 

The species distribution maps in the ‘Species accounts’ 

(Chapter 7) show some species are widespread within 

the south-west; presumably these are tolerant of varia-

tions in soils, landscapes and climates. One such species 

is M. concreta which, although restricted to the coastal 

plain country north of Perth, can occur on a wide range of 

substrates and in different parts of the landscape. Examples 

of other widespread species in the south-west are M. carrii 

and M. hamulosa. On the other hand, species such as 

M. agathosmoides and M. venusta are local endemics and 

probably have highly specific requirements as to soil type 

and landscape position.

Species richness is shown in Figure 9, and endemism 

is shown in Figure 10. The Biodiverse software version 

0.17 was used to generate the maps (Laffan et al. 2010) 

and the calculations were based on a 100 km grid. The 

final maps were then generated using ESRI ArcGIS ver-

sion 10.0. A continuous gradient from 1 to 72 species is 

shown in Figure 9 and this map depicts the lowest and 

highest richness. The endemism map (Figure 10) shows the 

unweighted endemism score for each grid cell calculated 

using equation (1).

Unweighted endemism 






where t is a taxon in the set of taxa T, and R


 is the global 

range of taxon t across the dataset (i.e. the number of cells 

in which it is found)

The number of Melaleuca species in south-eastern and 

eastern Australia is not high, although the phylogenetic 

diversity may not be greatly lower than that occurring in 

the south-west of the continent. Of particular note are the 

bottlebrush species (formerly Callistemon) of which about 

30 occur in the south-east and east and only four in the 

remainder of Australia. A few species occur in the arid 

zone but, in general, Melaleuca has not adapted well to very 

dry regions. Within the monsoonal tropics, members of 

the broad-leaved paperbark group are often dominant and 

may be a characteristic feature of the landscape. Several of 

the larger tree species of this group (M. argentea, M. leu-

cadendra, M. nervosa and M. viridiflora) occur across, or 

nearly across, the whole northern zone.

Ecological notes are provided for each species in the 

‘Species accounts’ (Chapter 7) but a brief overview for 

the genus is given here. Melaleuca species occur in a wide 

range of habitats (Figure 11). Many species are found in 

low to tall heathlands and shrublands, and some occur 

as low shrubs or trees in open eucalypt forests. A few 

species are found in wetlands, sometimes in open water, 

and some commonly occur on saline soils. No species are 

rainforest plants, although some apparently are able to 

survive encroachment by tropical rainforest, notably the 

broad-leaved paperbark M. leucadendra. The south-eastern 

and eastern M. pallida can occur in wet sclerophyll forest 

that may be considered temperate rainforest. Because of 

the range of climates, landscape positions and soil types 

to which Melaleuca species have become adapted, there is 

good scope for selecting species for trial in many applica-

tions, e.g. saline land reclamation, mining rehabilitation 

and ornamental and amenity use.

Locations of planted forests

Reliable information on plantation areas worldwide by 

species is largely unavailable. Of the three main com-

mercial species, M. quinquenervia is arguably the most 

widely planted. This species has been planted in numerous 

countries, including southern Africa, Central America 

(Costa Rica and Honduras), North America (southern 

California, Florida, Hawaii, Louisiana and in the extreme 

south of Texas), India, Fiji, Madagascar, Mexico, north-

ern Nigeria, the Philippines, Puerto Rico and the West 

Indies (Streets 1962; NAS 1983; Turnbull 1986; Geary 

1988; von Carlowitz 1991; CABI 2000; Dray et al. 2006). 

Two million trees have been planted on State Forest 

Reserve alone in Hawaii. Melaleuca quinquenervia was 

first introduced into southern Florida in the late 1800s, 

where it escaped cultivation on seasonally wet sites and 

has assumed weed status (NAS 1983). It occurs now on 

more than 200,000 hectares (ha) of wetlands in southern 

Florida (Turner et al. 1998).

Melaleuca cajuputi subsp. cajuputi has been planted 

since 1926 for oil production in central Java, Indonesia, 

using seed originally imported from the Maluku Islands. 

The extent of government-owned plantations on Java is in 

the order of 20,000 ha (Anto Rimbawanto, pers. comm. 

2012). It has been widely planted also in Malaysia and 

Vietnam. Melaleuca leucadendra is a relatively under-

utilised species. Most reports of plantings of this species in 

Africa, America and Asia refer to arboretum or trial plant-

ings rather than broad-scale plantations. The substantial 

literature on the cultivation of ‘M. leucadendron’ (e.g. see 

1   2   3   4   5

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