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In this article we will discuss about:- 1. Characters of Myrtaceae 2. Distribution of Myrtaceae 3. Economic Importance 4. Affinities 5. Important Types.
Characters of Myrtaceae:
Leaves aromatic, gland dotted, exstipulate, entire margin; flower hermaphrodite, actinomorphic, epigynous; calyx 4-5, gamosepalous, sometimes thrown off as a lid; corolla 4-5, free or united; stamens indefinite; carpels 2-5 syncarpous, ovary inferior, placentation axile; style and stigma simple; fruit a berry or drupe.
A. Vegetative characters:
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Habit:
The members of this family are mostly trees (Eucalyptus, Syzygium, Psidium) or shrub (Carreya) very rarely herbs. Some of the species of Eucalyptus may attain a height of 300 ft.
Root:
Tap root and branched.
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Stem:
Erect woody, branched, bark very shining, smooth and goes off in old trees (Eucalyptus); vascular bundle bicollateral.
Leaves:
Simple, opposite, alternate (Eucalyptus), or whorled, shortly petiolate, exstipulate or with minute stipule, gland dotted, coriaceous, evergreen. Leaves of Eucalyptus show adaptation to dry climatic and intense sunlight conditions and may become needle like and take up vertical position.
B. Floral characters:
Inflorescence:
Usually of cyme type, sometimes panicle cyme or corymbose cyme, proliferous drooping spike in Callistemon; axillary in Psidium; solitary axillary (Myrtus communis); trichotomous cyme (Syzygium); paniculate cyme (Eucalyptus).
Flower:
Pedicellate (Eucalyptus) or sessile (Callistemon), bracteate usually with two bracteoles (Callistemon), ebracteate (Eucalyptus) actinomorphic, hermaphrodite, epigynous sometimes perigynous; complete.
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Calyx:
Sepals 4-5, polysepalous or united, rarely reduced or thrown off like a lid as the flower opens (Eucalyptus) or entirely absent in some of Eucalyptus spp; quincuncial aestivation.
Corolla:
Petals 4-5 more or less circular in form, polypetalous sometimes gamopetalous and forming cap (Eucalyptus), quincuncial aestivation.
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Androecium:
Stamens indefinite, arranged in several whorls at the edge of the receptacle, polyandrous rarely mondadelphous (Callistemon); 5 and antipetalous in Melaleuca. In Melaleuca leucadendron the stamens are numerous but in five bundles opposite to petals, anthers dorsifixed or versatile, dithecous, small, introrse, connectives of anthers are usually gland dotted. In the bud condition the stamens are bent.
Gynoecium:
Carpels 2 to indefinite, syncarpous; perigynous to fully epigynous; inferior, two to many locular, axile placentation rarely parietal (Rhodamnia), 2 to indefinite anatropous or campylotropous ovules per loculus; style simple, long, stigma capitate.
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Fruit:
A berry (Psidium), capsule (Eucalyptus, Callistemon)-, drupe (Eugenia).
Seed:
Non-endospermic.
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Pollination:
Entomophilous. Insects are attracted by coloured stamens and floral parts.
Floral formula:
Distribution of Myrtaceae:
The family contains 100 genera and 300 species out of which India contributes 116 species. The chief centres of distribution are Australia and America.
Economic Importance of Myrtaceae:
1. Fruits:
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Some members of the family produce edible fruits e.g. Syzygium cumini (syn. Eugenia jambolana) (H. Jamun), Psidium guajava (Amrood) with edible fruits.
2. Oil:
The essential oils are obtained by the steam distillation of leaves and branches of Eucalyptus species.
3. Spice:
Syzygium caryophyllata (syn. Eugenia caryophyllata) yields the cloves of commerce. Clove oil (H. Laung ka tel) is extracted out of them.
4. Medicine:
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Eucalyptus oil is used in influenza. It is mixed with clove oil and used in rheumatism. The roots of Eucalyptus are purgative. Clove oil is antipyretic and largely used in gum troubles. The leaves of S. cumini are used in indigenous medicine for dysentery.
The fruits of Myrtus communis are carminative and given in dysentery, diarrhoea, and rheumatism.
5. Wood:
The wood of Eucalyptus and Psidium is used in engraving and making handles. In Australia the wood of Eucalyptus is used for railway sleepers, bridges and plywood industries.
6. Ornamental:
Many plants viz., Callistemon, Myrtus, Melaleuca leucadendron, Tristania, Eucalyptus are cultivated for their showy nature in the gardens.
Affinities of Myrtaceae:
Engler and Prantl placed the Myrtaceae in the order Myrtiflorae along with other 17 families. Wettstein, Bessey, and Hutchinson adopted the name Myrtales. Bentham and Hooker placed the family Myrtaceae along with Lythraceae, Combretaceae and Onagraceae.
Bessey supported the view that the order Myrtales is allied to Rosales in many respects and probably derived from it. The order Myrtales is also allied to Umbellales in epigyny, the number of carpels and in pendulous ovules. Hence the systematic position of Myrtales is just before the Umbellales.
Primitive characters:
1. Plants trees, shrubs and climbers.
2. Leaves simple and alternate.
3. Flowers hermaphrodite and actinomorphic.
4. Petals free.
5. Stamens numerous and free.
Advanced characters:
1. Flowers epigynous.
2. Calyx gamosepalous.
3. Gynoecium syncarpous and reduction in the number of carpels to two (Eugenia, Eucalyptus).
4. Ovules campylotropous.
5. Fruit simple.
6. Seeds non-endospermic.
Common plants of the family:
1. Callistemon (Bottle brush tree):
Filaments of the anthers are scarlet in colour and form brush like structure.
2. Eucalyptus:
Beautiful tall tree.
3. Eugenia caryophyllata:
The dried flower buds form the spice – the cloves (H. Laung).
4. Psidium guajava:
Small tree yielding the fruit guava (H. Amrood).
5. Myrtus:
Aromatic shrub with shinning leaves.
6. Carreya:
Large deciduous tree of shady places.
Division of the family and chief genera:
The family Myrtaceae has been divided into sub-families on the basis of fruit character.
1. Myrtoideae:
Fruit berry rarely drupe; leaves always opposite.
Tribe (i) Myrteae:
Ovary 2-5 locular. Psidium, Myrtus, Eugenia, Myrcia.
2. Leptospermoideae:
Fruit dry, leaves opposite or alternate.
Tribe (i) Leptospermeae:
Gynoecium multilocular, fruit loculicidal capsule. Eucalyptus, Callstemon, Tristania.
Tribe (ii) Chamaelaucieae:
Gynoecium monolocular, fruit one seeded usually dry. Calycothrix, Darwinia, Verticordia.
Important Types of Myrtaceae:
1. Callistemon citrinus (= C. lanceolatus D.C.) (Common name – Bottle brush or Laila Majnu) (Fig. 60.1)
Habit:
A large tree with crimson-yellow to red flowers.
Root:
Branched, tap root, deep feeders.
Stem:
Woody but upper portions herbaceous, erect, woody, branched, cylindrical and solid.
Leaf:
Ramal and cauline, simple, alternate, entire, acute, gland dotted, leathery, unicostate reticulate venation, with inframarginal veins.
Inflorescence:
Pendant spike, 4 to 8 inches long.
Flower:
Bracteate, bracts caducous but sometimes green, leafy and persistent; pedicellate or shortly stalked, complete, hermaphrodite, actinomorphic, pentamerous, epigynous, crimson- yellow to bright red.
Calyx:
Sepals 5, gamosepalous, imbricate, persistent, small and green.
Corolla:
Petals 5, polypetalous, obovate, quincuncial, small and coloured.
Androecium:
Stamens many, polyandrous, filaments long, basally conate and form a staminal sheath, dithecous, dorsifixed, introrse, filaments bright red, giving the same colour to the flower.
Gynoecium:
Bi-to tetracarpellary, generally tricarpellary, syncarpous, inferior, number of the locules as many as the carpels, many ovules in each locule, axile placentation, style long and curved, stigma flat.
Fruit:
A capsule
Floral formula:
2. Eucalyptus (Fig. 60.2):
Habit:
A cultivated tall tree.
Root:
Tap, branched.
Stem:
Erect, woody, solid, cylindrical, branched, glabrous, shining.
Leaf:
Alternate, petiolate, simple, exstipulate, lanceolate, gland-dotted, entire margin, apex acute, smooth, unicostate reticulate venation.
Inflorescence:
Umbellate trichotomous cyme.
Flower:
Ebracteate, pedicellate, complete, hermaphrodite, actinomorphic, pentamerous, epigynous.
Calyx:
Sepals 5, gamosepalous, forming a lid or cap which is thrown off as flower opens.
Corolla:
Petals 5, gamopetalous, corolla cap covered by calyx cap forming calyptra which falls off on the opening of flower, superior.
Androecium:
Stamens indefinite, polyandrous, stamens attached to the rim of the calyx tube, anthers dorsifixed, dithecous, introrse.
Gynoecium:
Tricarpellary, syncarpous, ovary inferior, trilocular, axile placentation, 3-6 ovules per loculus, stigma small.
Formal formula:
3. Syzygium cumini (syn. Eugenia jambolana) (Fig. 60.3):
Habit:
An evergreen tree.
Root:
Tap, branched.
Stem:
Erect, woody, cylindrical, solid, branched, smooth.
Leaf:
Opposite, petiolate, simple, exstipulate, ovate-elliptical, entire, unicostate reticulate.
Inflorescence:
Flower crowded in clusters on branches of lateral panicles; cymose.
Flower:
Pedicellate or sub-sessile, hermaphrodite, actinomorphic, pale green, epigynous.
Calyx:
Sepals 5, gamosepalous, calyx tube adnate to ovary, funnel shaped, superior, valvate aestivation.
Corolla:
Petals 4, polypetalous, falls off as the flower opens, imbricate aestivation.
Androecium:
Stamens indefinite, in several series, inserted around the mouth of calyx tube, anthers dithecous, dorsifixed introrse.
Gynoecium:
Bicarpellary, syncarpous, ovary inferior, bilocular, axile placentation, ovules many, style simple, linear, stigma terminal.
Floral formula:
