BOTANY AND TAXONOMY
ORIGIN | TAXONOMY | THE GENUS MANGIFERA L. | BOTANICAL DESCRIPTION | TREE SHAPES BRANCHING AND LONGEVITY | TREE | ROOT | LEAF | INFLORESCENCE | FLOWERS | POLLEN | FRUIT |
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Common mango (Mangifera indica L.) originated as alloploid and its native home was suggested as Eastern India, Assam to Burma or possibly further in the Malay region (Popenoe, 1920). Vavilov (1926) also suggested Indo-Burma region as the centre of origin of mango. Introduction of superior types into Malay region from India is also an evidence of its origin in India. Based on detailed study of the history, phyto-geographical distribution of allied species, fossil records, evidence of numerous wild and cultivated varieties in India, Mukherjee (1951) considered origin of genus Mangifera probably in Burma, Siam, Indo-china and the Malay peninsula, but the birth of common mango in Assam-Burma region and not in Malay. According to De Candolle (1884), 'It is impossible to doubt that it [the mango] is a native of south Asia or of the Malay archipelago, when we see the multitude of varieties cultivated in those countries, the number of ancient names, in particular a Sanskrit name, its abundance in the gardens of Bengal, of Deccan peninsula, and of Ceylon even in Rheede's time (i.e., 1683)’.
Based on the recent findings (Mukherjee, 1997 and Bompard and Schnell, 1997), the centre of origin and diversity of the genus Mangifera is now firmly established in Southeast Asia. However, the origin of Mangifera indica has been a matter of speculation for many years. The fossil record described by Seward (1912) provides few clues, as the only fossil bearing the imprint of a leaf of M. pentandra has ever been found in Assam. Mukherjee (195l) suggested that Mangifera indica first appeared during the Quaternary period. On the basis of ancient accounts of travellers and the written historical records, it was believed for many years that mango must have originated in India and spread outward from there to Southeast Asia and thence to the New World and Africa. Because northeastern India is at the northernmost edge of the distribution of the Mangifera species (Mukherjee, 1997), Hooker (1876) suggested that mango might have been naturalized in India. It is now apparent on the basis of taxonomic and recent molecular evidence that mango probably evolved within a large area including north western Myanmar, Bangladesh and northeastern India (Mukherjee, 1997)
Bompard and Schnell (1997) also suggested that great species diversity of Mangifera in Malay Peninsula, Borneo and Sumatra, the available evidence points to a Sudanic origin for the genus. This however must not minimize the particular importance to the region stretching from Myanmar to Indo-China as another centre of diversification, as attested by a range of species belonging the section Euantherae (section including M. calunera, M. cochinchinensis and M. pentendra). Further M. indica apparently originated in region on western border of the secondary centre of diversification mentioned above. Truly wild common mango trees have been recorded in Bangladesh (Chittagong Hills), northeastern India (Assam valley) and Myanmar. Owing to its cultivation and dissemination for thousands of years, in India semi-wild trees can be found in the forests throughout the subcontinent.
The genus Mangifera belongs to the order Sapindales in the family Anacardiaceae which is a family of mainly tropical species with 73 genera (c. 850 species), with a few representatives in temperate regions. The other distant relatives of Mangifera are cashew (Anacardium occidentale), gandaria (Bouea gandaria), pistachio (Pistacia vera), marula (Sclerocarya birrea), ambarella (Spondias cytherea), yellow mombin (Spondias mombin), red mombin (Spondias purpurea), imbu (Spondias tuberosa), dragon plums (Dracontomelum spp.) kaffir plum (Harpepbyllum caffrum), etc.. Malesia has been considered as the phytogeographic region extending from the Malay peninsula south of the Kangar-Pattani line to the Bismarck archipelago east of New Guinea (Whitmore, 1975). Apart from edible fruit Anacardiaceous species also yield other valuable products like wood, gums and resins, wax and varnishes and tanning materials. It is also a family well known for the dermal irritation produced by some of its members, including some Mangifera spp. whose resinous sap may induce allergic reaction.
The Genus Mangifera L.
The genus Mangifera consists of 69 species and mostly restricted to tropical Asia. The highest diversity occurs in Malaysia, particularly in peninsular Malaya, Borneo and Sumatra representing heart of the distribution range of the genus. The natural occurrence of all the Mangifera species extends as far north as 27o latitude and as far east as the Caroline Islands (Bompard and Schnell, 1997). Wild mangoes occur in India, Sri Lanka, Bangladesh, Myanmar, Sikkim, Thailand, Kampuchea, Vietnam, Laos, southern China, Malaysia, Singapore, Indonesia, Brunei, the Philippines, Papua New Guinea, and the Solomon and Caroline Islands. Maximum species diversity exists in western Malesia and about 28 species are found in this region.
Mangifera species are mostly distributed below 300 m but can occur at 600-1900 m above sea level. The species is found as scattered individuals in tropical lowland rain forests on well-drained soils. Most of the species (c. 44) are found on well drained soils, periodically flooded (9 spp.) and species like M. gedebe, M. griffithii and M. parvifolia occur in certain type of swamp forests. Mangifera bompardii, M. dongnaiensis and M. orophila are mainly found in sub-montane forests above 1000 m and occasionally up to 1500-1700 m above sea level whereas few species like M. caloneura, M. collina, M timorensis, M. zeylanica are acclimatize to seasonally dry climates in deciduous or semideciduous forests. M. sylvatica and wild M. indica can be found in Sikkim and southern China, at altitudes of 600-1900 m above sea level.
Tree shapes, branching and longevity
Mango trees, grown from seeds are known as "seedlings" have a long straight bole. Tree is sympodially branched (Scarrone's model). Grafted trees on the other hand are dwarf with spreading branches. However, the shape of the canopy also depends on the space available for its development. Isolated trees, getting sufficient space for their growth may differ in tree shape with the same variety grown in the orchard. On shallow soils the growth is stunted. Cultivars like Latra and Creeping are spreading in growth habit thus can be trained as creepers.
Considerable variation in canopy characteristics of Indian mango cultivars has been observed. The compactness of the canopy, branching pattern and leaf component show ecogeographical dependence also.
Seedling trees live much more than 100 years whereas grafted ones live only 80 years or less. One of the largest trees known is that from Chandigarh (India), with a trunk of 3.5m in diameter, limbs of 75cm diameter, the crown spreading over 2250 m2 with an annual production of about 16000 fruits in peak years at the age more than 100 years old (Singh, 1960). Seedling tree measuring a spread of 125 ft. and a girth of 25 ft. has been reported to exist in Brazil (Popenoe, 1920).
Tree is medium to large (10-40 m in height), evergreen with symmetrical, rounded canopy ranging from low and dense to upright and open. Bark is usually dark grey-brown to black, rather smooth, superficially cracked or inconspicuously fissured, peeling off in irregular, rather thick pieces. Exudate of the live bark transparent, a dark yellowish brown, drying brown, consisting of a resin mixed with a gum. The bark contains 78% resin and 15% gum in addition to tannic acid. Terminal bud small, enveloped by small, lanceolate acute bud scales. Twigs not very thick, smooth, apically angular, glabrous, glossy and dark green.
The tree forms a long unbranched long tap root (up to 6-8 m and more) plus a dense mass of superficial feeder roots. Feeder roots develop at the base of the trunk or slightly deeper; these produce anchor roots, and sometimes a collection of feeder roots develops above the water table. The fibrous root system extends away from the drip line. Effective root system of an 18- year old mango tree may observe a 1.2 m depth with lateral spread as far as 7.5m (Bojappa and Singh, 1974).
The leaves are simple, exstipulate, alternately arranged, 15-45 cm in length. The petiole varies in length from 1 to 12 cm, always swollen at the base. It is grooved on the upper side. The phyllotaxy is usually 3/8 but as the leaves are arranged very closely at the tips they appear to be whorled. Leaves are variable in shapes like oval-lanceolate, lanceolate, oblong, linear-oblong, ovate, obovate-lanceolate or roundish-oblong (Singh, 1960). The apex ranges from acuminate to nearly rounded. The margin is usually entire, sometimes slightly undulated and wavy, rarely twisted or folded. The length and breadth varies from 12 to 45 cm and 2 to 12 cm, respectively, depending on variety and growth. The secondary veins are quite prominent, and in some of the varieties range from eighteen to thirty pairs. The upper surface is shining and dark green while the lower is glabrous light green. The leaves appear in flushes. They are flaccid and pendulous when young. The colour of young leaves generally vary form variety to variety, generally being tan-red, pink, yellow-brown in colour. As the leaf grows, its colour changes from tan-red to green, passing through many different shades and become dark green at maturity.
The leaves have fibres and crackle when crushed. They strongly smell of turpentine (some cultivars do not smell). The leaves contain a good amount of mangiferin (xanthone). In India, it was obtained as "Indian Yellow" from the cow's urine. Cows were fed exclusively with mango leaves and ultimately excessive feeding on leaves lead to the death of the animal.
The inflorescence is pseudo-terminal, originating from a bud, together with the new leafy sprout; there are cultivars with lateral inflorescence. The inflorescence is a narrowly to broadly conical panicle up to a 45 cm long depending upon cultivar and environmental conditions during its development. It is usually bracteate, but may sometimes be ebracteate. The bract if present, is leafy, elliptical and concave. The colour of the panicle may be yellowish-green, light green with crimson patches or with crimson flush on branches. It is generally pubescent but sometimes may be glabrous. The branching of the inflorescence is usually tertiary, rarely quaternary, but the ultimate branching is always cymose (Singh, 1960). The panicle bear 500-6000 flowers of which 1-70% are bisexual, remainder are male depending on the cultivar and temperature during its development.
Hermaphrodite and male flowers are produced in the same panicle, usually with a larger number of the later. The size of both male and hermaphrodite flowers varies from 6 to 8 mm in diameter. They are subsessile, rarely pedicellate, and have a sweet smell. Pedicels are very short or missing; they are articulate with a panicle branch of the same diameter, which is often mistaken for the pedicel (Barfod, 1988). The calyx is usually fivepartite. The lobes are ovate-oblong and concave. The corolla consists of five pale yellow petals (rarely four to eight), which are twice as long as the calyx and contain three to five ridges on the ventral side. The petals are in bud imbricate and slightly contorted. They are thin, yellowish and after expanding horizontal, the upper half rather irregularly and not very pronouncedly reflexed, they are free at their base. The ridges are slightly dark. The upper half and the margin of the petal are white. On fading, the petals become pinkish. Between the corolla and androecium there is an annular, fleshy, and five-lobed disc (Singh, 1960; Kostermans and Bompard, 1993).
The androecium consists of stamens and staminodes, altogether five in number, of which usually one, or rarely two, are fertile and the rest are sterile. However, in cultivar Pico, three fertile stamens have been reported (Juliano and Cuevas, 1932). As many as ten stamens, which occur in other members of the genus, may also occasionally be found in the form of primordia only (Maheshwari, 1934). All the stamens are inserted on the inner margin of the disc. The position of the fertile stamen and pistil may be either parallel or oblique to each other (Naik and Gangolly, 1950). The fertile stamens are longer than the staminodes and are nearly equal to the length of the pistil. The colour of the anther is pink, which turns purple at the time of shedding.
The ovary is sessile, one-celled, oblique and slightly compressed in its lateral aspect. It is placed on the disc. The ovule is anatropous and pendulous, and shows one-sided growth. The style arises from the edge of the ovary and ends in a simple stigma. Sometimes three carpels may develop in a flower (Singh, 1960).
The pollen grains are of variable shapes, with the size varying from 20 to 35 micron (Mukherjee, 1950; Singh, 1954). Small amount of pollen is produced in M. indica; the grains are sphaeroidal to prolate sphaeroidal, radially symmetrical, subangular in polar view, isopolar, with a few giant triploid ones of up to 50 micron, they are 3-monocolporate, goniotreme, sides convex-subprolate; apertures equidistant and zonal; ecto-aperture (colpus) extends slit-like from pole to pole.
The fruit is a more or less compressed, fleshy drupe. It varies considerably in size, shape, colour, presence of fibre, flavour, taste and several other characters. The most characteristic feature of the mango fruit is the formation of a small conical projection developing laterally at the proximal end of the fruit, known as the beak. It may be quite prominent in some, less so in others, while in some varieties it is represented merely by a dot. A wide sinus is always present just above this beak. The pistillate area of the fruit located near the base of the beak is known as the nak. The shape of the fruit varies from rounded to ovate-oblong or longish, with the length varying from 2.5 to 30 cm in different varieties. The base may be depressed or elevated or may be intermediate. The skin is gland-dotted and at maturity its colour exhibit different mixtures of green, yellow, and red shades. It may be smooth or rough. The acrid juice, with turpentine like smell, present in the stalk or sometimes in the fruits, is known as chenp in Hindi is due to myrcene and ocimene. Its main irritating constituent has been identified as an allergenic urushiol, 5-heptadecenylreorcinol.
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