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Family Myrtaceae

Synonyms: Psiloxylaceae APNI*
Heteropyxidaceae APNI*

Description: Trees or shrubs.

Leaves opposite, alternate or occasionally whorled; laminas simple, usually with entire margins, venation usually pinnate (triplinerved in a few genera), very commonly dotted with conspicuous, translucent oil glands; stipule-like emergences minute or absent.

Inflorescences variable; flowers solitary or in umbel-like or raceme-like inflorescences or from dichasia to many-flowered panicles; sometimes aggregated into conflorescences that are head- or spike-like. Flowers actinomorphic, bisexual, mostly 4- or 5-, rarely 6-merous. Perianth segments usually free but sometimes forming various kinds of calyptra. Sepals usually 4 or 5, often reduced as lobes on edge of hypanthium, often persistent in fruit. Petals as many as calyx lobes, usually free and falling after anthesis, occasionally absent. Stamens usually perigynous, to almost epigynous, 5–numerous, free or grouped into 5 bundles opposite the petals; anthers versatile or adnate. Ovary usually half-inferior (varying from almost inferior to almost superior), 1- to multi-locular; style simple.

Fruit a loculicidal capsule, nut or berry, rarely drupe-like.

Distribution and occurrence: World: c. 145 genera, c. 5650 species, tropical to temperate regions, mainly S. America, Australia & Malesia. Australia: c. 70 genera, c. 1700 species, all States.

External links:
Angiosperm Phylogeny Website (Family: Myrtaceae, Order: Myrtales)

Myrtaceae is one of the top three species-rich families in Australia.

Text by Key updated by Peter G. Wilson, 17 Apr 2020
Taxon concept:

 Key to the genera 
1Fruit succulent.2
Fruit dry.18
2Inflorescences usually terminal and many-flowered; seed relatively large, usually solitary.3
Inflorescences axillary, 1 or few-flowered; seed usually small, mostly >1 per fruit, or sometimes only 1.
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3Seeds with a papery testa and separate, green cotyledons.Syzygium
Seeds with no obvious testa, cotyledons fused with a conspicuous dark inclusion spreading through the centre.
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4Fruit apex topped by the persistent, cylindrical, unexpanded free portion of the hypanthium; intercotyledonary inclusion spreading from the base of the fruit.Waterhousea
Fruit apex topped by the circular remnant of the hypanthium rim; intercotyledonary inclusion spreading from the summit of the fruit.
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5Leaves usually <10 mm wide; flowers solitary in leaf axils; plants of sclerophyll forest, rainforest, heath and scrubland.6
Most leaves >10 mm wide; flowers either solitary, clustered or in axillary raceme-like or panicle-like inflorescences; plants of rainforests, sometimes on their margins or in sclerophyll forest.
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6Mature fruit white to greyish or bluish green, often with darker spots; spreading or bushy shrubs to 2 m high; coastal districts and adjacent ranges north from the Sydney district.Austromyrtus
Mature fruit green turning red or black; shrubs or small trees to 12 m high; rare, only on the McPherson and Nightcap Ranges.
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7Mature fruit yellow, orange or red.8
Mature fruit purple or black.
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8Fruit vertically ribbed, bright red.Eugenia
Fruit not vertically ribbed, usually yellow to orange, sometimes red.
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9Sepals and petals mostly 4.10
Sepals and petals mostly 5, or occasionally some 4.
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10Leaves 3-veined from base; fruit red turning blackish when mature.Rhodamnia
Leaves not 3-veined from base; fruit yellow to orange.
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11Mature fruit >2 cm diam.; sepals cohering in the bud, splitting longitudinally at flowering.Psidium
Mature fruit <2 cm diam.; sepals free in the bud.
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12Leaves 1–3 cm wide; ovary 3-locular; mature fruit 5–7 mm diam., topped by erect persistent sepals; petals 4–6 mm long.Archirhodomyrtus
Leaves 2.5–6.5 cm wide; ovary 4-locular , becoming multi-locular by development of false septa; mature fruit 10–15 mm diam. with persistent sepals reflexed; petals 7–10 mm long.
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13Sepals and petals 4.14
Sepals and petals 5.
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14Leaves 3-veined from base.Rhodamnia
Leaves not 3-veined from base.
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15Fruit vertically lobed; ovary 4- or 5-locular.Decaspermum
Fruit not vertically lobed; ovary 2- or 3-locular.
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16Petals 2–5 mm long; testa hard and bony.17
Petals 5–7 mm long; testa membranous to papery.
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17Anthers with a conspicuous apical appendage; flowers and fruit usually solitary, pendent.Uromyrtus
Anthers topped only by a small apical gland; flowers and fruit occasionally solitary, but usually >1, not pendent.
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18Flower buds covered with a calyptra formed from the fused perianth segments.19
Flower buds not covered with a calyptra.
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19Inflorescences compound, terminal or axillary and anthers versatile and opening by parallel slits and disc steeply depressed in fruit.Corymbia
Inflorescences, anthers and fruit not a combination of the above characters.
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20Stamens grouped (usually distinctly fused) into 5 bundles opposite the petals21
Stamens not in 5 bundles, usually free but occasionally fused into a short tube at the base.
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21Fruit included in the hypanthium or barely exserted; seeds linear.22
Fruit exserted from the hypanthium; seeds flat, winged.
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22Flowers sessile, aggregated into head- or spike-like conflorescences.Melaleuca
Flowers pedicellate, inflorescences cymose.
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23Leaves opposite and decussate; oil ducts absent from the petioles.Tristania
Leaves alternate along branchlets but clustered in false whorls at the end of the branchlets; oil ducts, containing milky oil, present in the petioles.
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24Leaves opposite.25
Leaves alternate.
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25Most leaves >5 mm wide.26
Most leaves <5 mm wide.
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26Fruit indehiscent; hypanthium papery to leathery27
Fruit a loculicidal capsule; hypanthium woody
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27Leaves with a strong aniseed smell when crushed, margins undulating.Anetholea
Leaves not strongly smelling of when crushed, margins ± flat.
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28Flowers sessile, 7 per inflorescence; capsules fused in a woody syncarp.Syncarpia
Flowers pedicellate, numerous; capsules usually ribbed.
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29Ovary and fruit 2- or 3-locular.30
Ovary and fruit 1-locular.
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30Stamens exceeding the petals.Kunzea
Stamens shorter than the petals.
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31Ovary and fruit 2-locular.Baeckea
Ovary and fruit 3-locular.
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32Anthers adnate to filament, dehiscing by pores or short parallel slits.33
Anthers versatile, dehiscing by long parallel slits.
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33Inflorescence usually of solitary flowers; bracteoles 2; peduncles generally shorter than pedicels34
Inflorescence usually of (2–)3 or more flowers; bracteoles 4–many, clustered at the apex of the peduncle; peduncles generally longer than pedicels
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34Sepals ‘compound’, the dorsal lobe often acute; summit of fruit slightly exserted from the fruiting hypanthium; leaves acute to obtuseKardomia
Sepals simple, obtuse; summit of fruit at or within the rim of the fruiting hypanthium; leaves with a small, recurved mucro
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35Ovules and seeds D-shaped, angular.Baeckea
Ovules and seeds ± reniform, not angular.
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36Some stamens opposite centre of petals44
No stamens opposite centre of petals.
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37Stamens 5–8; ovules 2 per loculus.Ochrosperma
Stamens 14–18; ovules 8–13 per loculus.
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38Stamens 10, twice as many petals, alternating with 10 staminodes; style long-exserted.39
Stamens 5–12, up to twice as many as petals, staminodes lacking; style included or very shortly exserted.
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39Sepals terminating in one or more slender processes.Homoranthus
Sepals lacking slender processes, entire or shortly ciliate.
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40Stamens <10, usually opposite the sepals; anther connective gland prominent, clavate or ± urceolate.Thryptomene
Stamens 10 or 12 or if 5 then opposite the petals; anther connective gland small, subglobose.
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41Ovary 1-locular; sepals persistent, membranous, terminating in a long, slender awn.Calytrix
Ovary >1-locular; sepals persistent or not persistent, never ending in an awn.
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42Stamens considerably longer than the petals.43
Stamens shorter, or scarcely longer, than the petals.
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43Sepals not persistent, flowers aggregated into spike-like conflorescences.Callistemon
Sepals persistent, flowers in heads or solitary in the leaf axils.
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44Shrubs; pedicels shorter than, or as long as, the leaves; bracteoles not persistent.Rinzia
Prostrate plants; pedicels longer than the leaves; bracteoles persistent.
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