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Kerala is a land of intense
cultivation. Several exotic species have been introduced as cash crops. They are
raised in pure crops or as mixture along with indigenous species. Coconut,
arecanut and paddy are the most extensively raised indigenous species. A variety
of herbaceous as well as shrubby species are often grown along with coconut and
arecanut. Whereas paddy is raised as a pure crop. Tea, coffee and rubber are the
extensively raised exotic cash crops in the State. Tapioca, cashew, coco and
tobacco are also cultivated to a large to medium scale. The exotic trees
introduced to meet the timber, pulp and paper industry are Acacia
auriculiformis, A. mangium, A. mearnsii, A. dealbata, Eucalyptus grandis, E.
tereticornis, E. camaldulensis, Grevillea robusta, Paraserianthes falcataria,
Swietenia macrophylla, etc. Exotic ornamental and avenue trees are
Bauhinia purpurea, Callistemon citratus, Cananga odorata, Cassia siamea, C.
nodosa, Couropita guianensis, Delonix regia, Jacaranda mimosifolia, Kigelia
africana, Kleinhovia hospita, Peltophorum pterocarpum, Plumeria rubra,
Polyalthia longifolia, Spathodea campanulata, etc. The important
horticultural plants are Achras sapota, Averrhoa bilimbi, A. carambola,
Diospyros mangostana, Phyllanthus acidus, Psidium guajava, Syzygium aqueum, S.
jambos, S. malaccensis, etc.
A few species
which were introduced as garden plants have become naturalised and attained the
status of weed. The most widespread and obnoxious weeds are Ageratina
adenophora, Chromolaena odorata, Eichhornia crassipes, Lantana camara, Mikania
micrantha, Mimosa diplotricha and Parthenium hysterophorus. These aggressive
weeds are establishing very fast in the terrestrial as well as aquatic
ecosystems and are serious threat to the indigenous flora. It is estimated that
about 10 per cent of the flora of the State is composed of exotic species.
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