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In this article we will discuss about:- 1. Characters of Cactaceae 2. Distribution of Cactaceae 3. Economic Importance 4. Affinities 5. Important Types.
Characters of Cactaceae:
Plant fleshy with tufts of thorns; stems flattened, jointed, succulent, apparently leafless; flowers large, usually solitary, hermaphrodite, epigynous; tepals indefinite with gradual transition from sepals to petals, stamens indefinite, Carpels syncarpous, ovary inferior unilocular, parietal placentae; fruit berry.
A. Vegetative characters:
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Habit:
The plants are mostly perennial xerophytic shrubs rarely trees, sometimes epiphytes.
Root:
Tap-root, raher small and shallow.
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Stem:
Fleshy, of various shapes, rarely bearing normal leaves, usually provided with spines or barbed bristles (glochidia) which are generally considered to be modified leaves; spines and glochidia develop from small cushion-like structures called areoles; in several genera, the stem assumes leaf-like flattened from phylloclades.
Leaf:
Mostly leafless, leaves reduced to spines, in Opuntia, true leaves are very small, appear early and fall very soon leaving the phylloclades to do the assimilation work, spines or tuft of bristles developed from areoles.
B. Floral characters:
Inflorescence:
Solitary rarely paniculate.
Flower:
Exceptionally beautiful, large, showy but only very rare (Mammillaria, Opuntia, Cereus, Echinocereus, Schiumbergera); sessile, mostly bisexual and actinomorphic or nearly zygomorphic, epigynous.
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Periantl:
Tepals numerous showing a gradual transition from sepals to petals; spirally arranged; sepals often petalloid; petals epigynous and present in several series; often fuse to form a perianth tube or hypanthium.
Androecium:
Stamens numerous, in several series or groups, epipetalous or inserted at the base of petals; anthers 2-celled, basifixed, introrse; longitudinally dehiscent.
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Gynoecium:
Two or many carpels, syncarpous; ovary inferior, unilocular, numerous anatropous ovules; parietal placentation, very rarely basal placentation; style 1 and simple; stigmas often as many as the carpels.
Fruit:
Many seeded berry.
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Seed:
Scanty or no endosperm.
Pollination:
Entomophilous.
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Floral formula:
Distribution of Cactaceae:
Cactaceae consists of about 87 genera and 2,000 species. Members are distributed mainly in semi-desert and hot-desert regions of tropic and sub-tropic of America, Mexico.
Economic Importance of Cactaceae:
1. Food:
Fruits of Lophophora williamsii, Nopalea cochenillifera and several species of Opuntia are edible.
2. Fodder:
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In emergency i.e. fodder famine prevails the spines of Opuntia are burnt, by scorching and then used as fodder.
3. Dye:
A scarlet dye – cochineal is prepared from Cochineal insects that feed upon Opuntia tuna, Napalea cochenillifera.
4. Medicinal:
Some species of Opuntia and Cercus have medicinal properties.
5. Ornamentals:
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In rock gardens and unusual environment the use of Cacti – Marnmillaria, Cereus, Echinocactus, Rebutia, Opuntia etc., has become extensive.
Affinities of Cactaceae:
Cactaceae is of special interest to botanists for its combination of a primitive, unspecialized flower with highly advanced vegetative organs. To the taxonomist it presents great problems, being apparently still in a state of active evolution.
As regards the position and relationship of Cactaceae, many views have been put forward. Engler retained it in the Opuntiales near the Myrtiflorae and admitted an alliance with the Aizoaceae. Bessey regarded the Cactales to be related to the Cucurbitales. Wettstein included the Cactaceae in the Centrospermae. Bentham and Hooker placed the family in the Ficoidales before the Umbellales and after the Passiflorales.
Rendle opined that “the affinity of the family is very doubtful”; he set it up within the Opuntiales, lying between the Myrtiflorae and Umbelliflorae. In Hutchinson’s arrangement, the Cactaceae appeared under the Cactales which was again put in between the Cucurbitales and Theales. On the basis of epidermal structures, floral plan and serological data, Mez considered the family as linked to the Loasaceae and the Parietales complex.
Buxbaum (1944) derived the Cactaceae from the Phytolaccaceae and took it to exemplify parallel evolution with the Aizoaceae. Evidence pooled from anatomy, embryology and floral morphology led Maheshwari (1945) and others to suggest that this family should be assigned to a position within or near the Centrospermae.
Gundersen (1950) treated the family in the Cactales near the Ranales. Mitra (1964) supported Gundersen’s contention of a ranalian relationship as expressed by Anemarrhena type of seedling, spirocyclic flowers (simulating Euryale), transition from sepals to petals and fasciculate androecium.
Common plants of the family:
1. Opuntia elatior – is an example of Cladode.
2. Opuntia dillenii – Prickly pear H. Chittar thor.
3. Cactus indicus – grown in hills as a hedge and sometimes found in plains.
4. Cereus peruvianus – Phylloclades 5-angular.
5. Marnmillaria – exceptionally beautiful large and showy.
Division of the family and chief genera:
The Cactaceae is divided into three subfamilies:
Sub-family I. Cereoideae:
Succulents with leaves reduced to minute scales and areoles without glochidia. Flowers funnelform of salverform. Examples – Cereus, Echinocactus, Mammillaria, etc.
Sub-family II. Opuntioideae:
Succulents with usually flattened jointed stems, small cylindrical to subulate caducous leaves and glochidiate areoles. Flowers rotate. Examples – Nopalea, Opuntia, etc.
Sub-family III. Pereskioideae:
Plants with flat leaves. Flowers in panicles. Example – Pereskia.
Important Types of Cactaceae:
1. Selenicercus flagelliformis (Fig. 65.1)
2. Opuntia dillenii (Prickly-pear; Vern. Chittar thor) (Fig. 65.2)
Habit:
A spiny, gregarious, perennial shrub about 1.5 metres high, xerophytic.
Root:
Tap-root.
Stem:
Flattened into phylloclades, jointed, joints, 30-40 cm. by 15-20 cm. broadly obovate, undulate, not very thick, bluish to bluish-green, covered with little groups of spines.
Leaf:
Reduced, ½ in. long, pale-green, caducous, represented by clusters of spines as areoles, each tuft of 4-6 prickles, the largest (glochidia) very stout, subulate, firm and sharp, 1 to 1 ½ in. long usually somewhat curved, yellowish.
Inflorescence:
Solitary.
Flowers:
Bright yellow tinged with orange, 1-3 in. across, sessile regular, bisexual, acyclic, epigynous.
Perianth:
Indefinite, not sharply distinguishable from one another, the outer sepaloid showing gradual transition into petals in several series, spirally arranged, spreading imbricate, the innermost largest, obovate rounded, mucronate; the outer ovate, acute or rounded with membranous margins, superior.
Androecium:
Stamens indefinite, free, of unequal length inserted to the base of the inner perianth (epiphyllous) on the margin of the calyx-tube, superior, dorsifixed bithecous, introrse.
Gynoecium:
Carpels many, syncarpous; ovary inferior, unilocular, with 5-8, many ovuled parietal placentae, style single; stigmas 5-8, erect.
Fruit:
Berry, pyriform truncate, depressed at the apex, often angular, warty when not fully ripened, deep reddish-purple when ripe, edible.
Seed:
Non-endospermic.
Floral formula:
