James Mathew, B.Ed. student, St. Thomas College of
Teacher Education, Pala
Abstract
Exotic plants are alien, non-native, non-indigenous or introduced plant species that occur in areas outside of their natural geographic zone. They may be introduced into an area from outside its native range either purposefully or accidentally. These plant species have role in floristic biodiversity, ecosystem processes, medicinal field and economic benefits. Although while analyzing the current status of exotic plants in the Kottayam district it is found as 66 exotic plant species in 38 families. This found that the invasion of such plants is being found in and around us.
Keywords
Non-indigenous,
Exotic, Oxalidaceae, Stericuliaceae, Portulacaceae
INTRODUCTION
Invasive alien species are those which
spread outside their normal distribution range and become invasive in their new
geographic area. Their spread is aided by international trade and tourism
especially import of goods items such as seeds, grains, fruits pets, etc at the
new place, they escape the predator pressure, which kept their population in
check in the native range, and thrive outcompeting and displacing native species,
with its long-time maritime history, paved way for introductions were for
specific purposes such as agriculture, forestry, ornamentals and the like-
introduction of the rubber tree in point. Invasions by exotic plant species are
occurring at unprecedented rates as a result of human activities that have
increased the number of introductions and the rate of spread of many species.
It may happen either accidently or purposefully to new areas These invasions
have serious consequences for native biodiversity, disturbance regimes, and
ecosystem structure and functioning and therefore, these invasions are
considered a significant component of global change. Thus, identifying the
factors that influence invasions by exotic plants species is of critical
importance. Plant invasions are limited primarily by dispersal of propagules or
by the number of propagules entering a community. In the absence of dispersal limitations,
the ability of exotic species to successfully invade, that is, to persist and
spread in a community, may be influenced in part by the susceptibility of a
community to invasion. Several hypotheses have been proposed to explain why
some plant communities are more prone to invasions.
Exotic plants shows both positive and
negative impacts. In which the positive side of exotic plants, that is the food
and medicinal importance of exotic plants. And also, it shows these plants
could fill niches in degraded ecosystems and helps to restore native
biodiversity in an inexpensive and self-organized way that requires little or
no human interventions. In certain cases, they are actually quite beneficial,
and perhaps it’s time to recognize that, In California, for example, native
butterflies feed on non-native plants. In Puerto Rico, alien trees help to
restore abandoned pastures to a condition suitable for native plants, a variety
of underappreciated invasive roles are described, providing ecosystem services
replenishing human damaged and generally helping to sustain some resemblance of
natural health even as many ecosystems struggle to survive.
The introduction of alien species takes a long
benefit to some areas, for example when used in agriculture, animal faming, wood
production, medicine, aesthetic enjoyment hunting or trade of ornamental
plants. They can even have a positive effect in natural environment for example
when they function as a food resource for native species or when they replace
vegetation cover that had previously been damaged. Nevertheless, we should
consider these positive effects very carefully, because in almost every case,
if not in all, the benefits run into harmful long-term effects to natural environment
and species, but exotic plants have more negative effects, as an invader it
moves from an established source population, where intraspecific competition is
relatively high, to invasions front where interspecific competition dominates.
Invasive species are stock villains of conservation biology, disrupting
ecosystem and throwing native populations into disarray.
However, many non-native species do
enormous environmental damage. Invading species can cause complex changes
within the structure and function of their new ecosystem. Their presence can lead
to the reconstructing of established food webs, the importation of new diseases
to the new surroundings, and competitions with indigenous organisms for space
and food. The invasive alien species which leads to negative impacts are in a
group that includes fire stimulators and disruptors, water depletes, diseases
causers, crop damages, forest destroyers, fisheries disruptors, impeders of
navigations, clogger of water, destroyers of homes and gardens, species
eliminators and modifiers of evolution. Impacts of invasive species may also
change over time in response to local adaptions and shifts in community
composition. A community that is evolutionarily native to an invader may take
time to develop appropriate competitive, consumptive or avoidance response.
Exotic invasive species can directly and
indirectly influence natural ecological communities by modifying structure,
decreasing diversity, and altering ecosystem function. Specifically, exotic
plant species alter the hydrology of ecosystems, increase soil erosion,
decrease native plant diversity, and alter fire cycles. The objective of the
study was to determine exotic plants present in nearby locality.
REVIEW OF
LITERATURE
Abraham et al., (2009) revealed
that the exotic perennials appear to be less affected by the priority effects
arising from earlier germination by European annual grasses. In addition, these
species interactions in California grasslands may be mediated by increasing
anthropogenic or natural soil nitrogen inputs. They conducted a greenhouse
experiment to test the effects of order of emergence and annual grass seedling
density on native and exotic perennial grass seedling performance across
different levels of nitrogen availability.
Bennett et al.,
(2011) study recommended that how these multiple factors (direct competition,
mammalian herbivory, and soil-mediated effects and feedbacks) influence the
impact of H. lanatus on a common, native perennial seaside daisy (Erigeron
glaucus) using greenhouse and fi eld experiments. We tested
whether soils from beneath H. lanatus, native plant communities, and
sites restored with the native grass Calamagrostis nutkaensis influenced
E. glaucus germination, establishment, and growth in the greenhouse and
the fi eld. Using experimental ex-closures, we also tested for effects of
mammalian herbivory, direct competition from H. lanatus, and their
interaction on E. glaucus germination and establishment in the field
Crooks
(2002) in the study characterize potential effects of exotic engineers on the
physical environment, provide some examples of how the physical alteration of
ecosystems affects other biota, identify patterns in community level responses
to invader-induced changes in habitat complexity, and discuss how the
recognition of engineering and habitat modification affects the classification
of invaders’ ecosystem-level effects.
According to Blumenthal (2006) the
possibility that two mechanisms of invasion, release from natural enemies and
increased resource availability, may interact. When plants invade new
continents, they leave many herbivores and pathogens behind. Species most
regulated by enemies in their native range have the most potential for enemy
release, and enemy regulation may be strongest for high-resource species. High
resource availability is associated with low defence investment, high
nutritional value, high enemy damage and consequently strong enemy regulation.
Therefore, invasive plant species adapted to high resource availability may
also gain most from enemy release.
Ehrenfeld et al., (2006) propose
that plant secondary chemistry may be a useful trait for assessing the
likelihood of ecosystem (and community) impacts. Information about such traits
is readily available from several sources, rendering it a good candidate for
screening and monitoring programs. Plant secondary chemicals affect a variety
of ecosystem processes, largely through their direct and indirect impacts on
soil microbial community composition and function. They also have well-known
effects on human physiology, as evidenced in the numerous plant-derived
bioactive compounds used for their medicinal and other physiological effects.
There is a large amount of information available about plant secondary
chemistry due to its role in herbal medicine, dietary supplements and the emerging
field of nutraceuticals. This information includes databases and traditional
texts in ethnobotany, plant chemistry, and alternative medicine. I review
evidence that secondary compounds are widespread in invasive species and affect
soil microbial communities and microbially-mediated ecosystem processes.
Invasion ecology may profit from collaborations with a novel group of
scientists, including those in ethnobotany, nutraceuticals, plant chemistry and
alternative medicine.
Carpenter et al., (2005) proposed about
naturally occurring leaf herbivory in nine invasive and nine non-invasive
exotic plant species sampled in natural areas in Ontario, New York and
Massachusetts, and found that invasive plants experienced, on average, 96% less
leaf damage than non-invasive species. Invasive plants were also more
taxonomically isolated than non-invasive plants, belonging to families with 75%
fewer native North American genera. However, the relationship between taxonomic
isolation at the family level and herbivory was weak. We suggest that invasive
plants may possess novel phytochemicals with anti-herbivore properties in
addition to allelopathic and anti-microbial characteristics. Herbivory could be
employed as an easily measured predictor of the likelihood that recently
introduced exotic plants may become invasive.
Singh
et al., (2016) discussed the absorption of 26 plant species of exotic
origin, before 8th century, as evidenced by archaeological sculptural or
botanical remains and documentation of such plants in Sanskrit, the Vedic
language. Occurrence and/or introduction of such plants at such distant places
in ancient times is visualized as a result of geographical continental
fragmentation followed by drift, natural or man-made transoceanic movement, and
cultural and trade exchange of plant material over time.
Ricklefs et al., (2006) analyzed
the native and alien geographic ranges of all 1567 plant species that have been
introduced between eastern Asia and North America or have been introduced to
both regions from elsewhere. The results reveal correlations between the spread
of exotics and both the native species richness and transportation networks of
recipient regions. This suggests that both species interactions and human‐aided
dispersal influence exotic distributions, although further work on the relative
importance of these processes is needed
Reddy et al., (2008) deals with
comprehensive list of invasive alien species in the flora of India with
background information on family, habit and nativity. Total 173 invasive alien
species belonging to 117 genera under 44 families were documented. It was
prepared based on history, species origin, species behaviour and field
observations. Literature and websites were consulted extensively for relevant
publications. Almost 80% of the species were introduced from neotropics.
Tropical America (74%) and Tropical Africa (11%) contribute maximum proportion
to the invasive alien flora of India. Habit wise analysis shows herbaceous
species share 151 species, followed by shrubs (14), climbers (5) and trees (3).
A better planning is needed for early detection and reporting of infestations
of spread of new and naturalized weeds to monitor and control.
Mangla et al., (2007) investigated
the role of a native generalist soil pathogen through which a non‐native
invasive plant species may suppress naturalized/native plant speciesSoils
collected beneath Chromolaena in the Western Ghats of India inhibited
naturalized/native species and contained over 25 times more spores of the
pathogenic fungi Fusarium semitectum than soils collected at the same locations
beneath neighbouring native species that were at least 20 m from any
Chromolaena plant. Sterilization of these soils eliminated their inhibitory
effect. Chromolaena root leachate experimentally added to uninvaded soils
increased Fusarium spore density by over an order of magnitude, and increased
the inhibitory effect of the soils.
Putten et al., (2014) proposed that
using untargeted metabolomic fingerprinting, we compared a broad range of
metabolites of six successful exotic plant species and their native congeners
of the family Asteraceae. Their results showed that plant chemistry is highly
species‐specific and diverse among both exotic and native species. Nonetheless,
the exotic species had on average a higher total number of metabolites and more
species‐unique metabolites compared with their native congeners. Herbivory led
to an overall increase in metabolites in all plant species. Generalist
herbivore performance was lower on most of the exotic species compared with the
native species. They conclude that high chemical diversity and large
phytochemical uniqueness of the exotic species could be indicative of
biological invasion potential.
Putten et al., (2010) propose that
there are three main pathways by which this can happen. First, plant–soil
feedback interactions in the invaded range are neutral to positive, whereas
native plants predominantly suffer from negative soil feedback effects. Second,
exotic plants can manipulate local soil biota by enhancing pathogen levels or
disrupting communities of root symbionts, while suffering less from this than
native plants. Third, exotic plants produce allelochemicals toxic to native
plants that cannot be detoxified by local soil communities, or that become more
toxic following microbial conversion. They discuss the need for integrating
these three pathways in order to further understand how soil communities
influence exotic plant invasions.
NEED AND
SIGNIFICANCE
Exotic species
are used as an alternative in many places where local indigenous forests cannot
produce the type, quantity and quality of forest products required. In
general, exotic species have growing rates much greater than native species;
therefore, they produce more wood per unit of area and time. In the tropics,
exotic species could grow 5 to 10 times more wood than native species. Many of
the exotic species used in forestry plantations can grow in sites with limited edaphological
conditions (as pH, nutrient availability, moist content, texture, etc.) with
better yield than indigenous species. Exotic species usually can adapt to
different environmental conditions; nevertheless, is important to test the
exotics in the zone where it is needed prior deciding a large-scale plantation
establishment. With features as fast growing and
wider adaptation, exotic species could be used as source of different type of
products and so reduce the pressure over native species (which in general
growth less and slower).
The plantation of
exotic species should be selected carefully, after introduction to a site if
the provenances and seed sources of the exotic species are not appropriate, the
plantation could result in a disaster. Therefore,
it is important to test the species in the area where it is to be grown before
it is planted at commercial scale. The delayed failure, in some cases creates a
problem during afforestation in later stage.
In some case, the introduced species is performed at substandard
level. Sometimes growth may become
unsatisfactory. The exotic is considered
ecologically less valuable than indigenous species. The use of exotic species
could be associated with new pests and diseases and affect native species
e.g. pink disease eucalyptus
grandis. Therefore, it implies new or
stricter disease and pest controls. The exotic may bring new insect and pest to
be introduced at the region. Experimentation
with exotic is time consuming and may not serve the purpose of immediate needs.
OBJECTIVES
OF THE STUDY
·
To know the importance of Exotic
plants.
·
To know the significance of
Exotic plants in Biodiversity.
·
To identify the different Exotic
plants nearby locality.
TAXONOMIC DESCRIPTION OF THE
EXOTIC PLANTS
FAMILY:
ANNONCEAE
1. Annona muricata L.
Malayalam Name(s):
Cancer chakka, Mullanjakka, Mulluathi, Mullathi
English name(s):
Soursop, Guanabana, Graviola, Prickly Custard Apple
Description:
Trees, to 10 m high, bark pale brown; young twigs glabrescent. Leaves simple,
alternate,
distichous, estipulate; petiole 4-8 mm long, slender, glabrous, grooved above;
lamina
7-14.5 x 3-5.5 cm,
elliptic, oblong, obovate, oblong-obovate, elliptic-oblong or elliptic-obovate,
base acute, apex
acute to acuminate, coriaceous, margin entire, lateral veins 8-10 pairs,
slender,
pinnate,
prominent, intercostae reticulate, domatia present. Flowers yellowish-green,
solitary, axillary or from mature branches; sepals 3,
triangular, persistent; petals 6(3+3) ovate-acute, yellow, thick, glabrous,
outer ones 2.5-3.5 x 2-2.5 cm, base cordate, apex acuminate, inner petals ca.
1.5 x 1 cm, shortly stipitate; stamens many, 4-5 mm long, linear, filaments
broad at base, with capitate top of the connective; ovary superior, ca. 4 mm
long, linear, slightly curved, strigose, style broad at base, stigma entire.
Fruit ovoid to obovoid, 15-25 x 10-15 cm, green, covered with curved spines,
stalks 2-3 cm long, stout; seeds many, reddish-brown, ca. 1.5 cm long.
Uses: Medicinal
Habitat: Cultivated
Distribution: Native of Central America and West Indies
2. Annona reticulata L.
Malayalam Name(s): Manilanilam, Ramasita, Aatha,
Ramachakkamaram, Vlathi, Parankichakka
English name(s): Custard apple, Bullock's heart
Description: Trees, to 8 m high; bark pale brown.
Leaves simple, alternate, distichous, estipulate; petiole 10-20 mm long, stout,
glabrous, grooved above; lamina 10-20 x 3.5-7 cm, ovate-lanceolate, oblong, lanceolate
or oblong-lanceolate, base acute, obtuse or decurrent, apex acuminate, margin
entire, pubescent on both sides when young, glabrous above and pubescent
beneath at maturity, coriaceous; lateral nerves 10-14 pairs, pinnate,
prominent, intercostae 24 reticulate. Flowers bisexual, green, several from
internodal cymes, rarely leaf opposed; sepals 3, 2-3 mm long, pubescent
outside, glabrous within; petals 3 + 3, outer ones 1.5-2 cm, puberulous; inner
ones reduced; stamens many, 1-1.3 mm long; anther cells hidden by the
overlapping connectives; carpels many. Fruit an aggregate of berry, to 10 cm
across, spherical or ovoid, yellowish-red; areoles flat, rather separated by
reticulations of raised ridges; pulp yellowish; seeds black-brown.
Uses: Medicinal
Habitat: Cultivated and often naturalised
Distribution: Native of Central America and West
Indies
FAMILY: PORTULACACEAE
3. Talinum portulacifolium (Forssk.)
Malayalam Name(s): Badhalacheera, Vassalacheera,
Sambarcheera
Description: Erect semi-succulent, glabrous herbs to 1
m tall; rootstock tuberous. Leaves 30 subsessile, alternate, 4-8 x 1.5-3 cm,
obovate or oblanceolate, base cuneate, apex obtuse or rounded. Inflorescence
terminal, paniculate. Flowers 1.5-2 cm across; pedicels to 1.2 cm long; bracts
2-4 mm long, linear. Sepals 2, 4-6 x 2-3 mm, ovate-lanceolate, acuminate.
Petals 5, pink, 8-10 x 4-5 mm, obovate. Stamens many; filaments unequal. Ovary
c. 2 mm long, globose, 1- loculed; styles 3-armed. Capsules 4-6 mm across,
globose. Seeds ovoid, black, striate.
Uses: Used in curries
Habitat: Wastelands
Distribution: Pantropical
FAMILY: GUTTIFERACE
4. Garcinia mangostana L.
Malayalam Name(s): Mangosta, Mangustan
English name(s): Mangosta, Mangustan, Mangosteen
Description: Evergreen trees, to 20 m high, bark black
or dark brown, smooth; exudation yellow, sticky; branchlets decussate, stout,
cylindric, slightly grooved, glabrous. Leaves simple, opposite, decussate,
estipulate; petiole 20-25 mm long, stout, glabrous, slightly grooved above,
ligulate projections at base prominent, clasping the branches; lamina 8-25 x 4-
12 cm, elliptic to elliptic-oblong or ovate-oblong, base acute, obtuse or
rotund, apex acute or shortly acuminate, margin entire, often slightly revolute,
glabrous, thickly coriaceous, glossy; 32 lateral nerves numerous, parallel,
close, slender, prominent, looped near the margin forming intramarginal nerve,
intercostae reticulate, obscure. Flowers polygamodioecious; male flowers : pale
green, to 4 cm across, 3-9 in terminal fascicles; pedicels 1.5-2 cm long;
bracts orbicular, concave, scarious; sepals 4, erect, unequal, coriaceous,
concave; petals 4, larger than sepals, ovate, fleshy, yellow-red inside, green
red outside; stamens numerous, inserted on 4 thick, receptacular lobes below
the rudimentary pistil; filaments short; anthers ovate-oblong, recurved;
rudimentary pistil discoid, fleshy, red, apex conical, as long as stamens;
bisexual flowers: 1-2 at the apices of branchlets, purple; pedicel 1.8-2 cm
long, stout, woody; sepals 4, rarely 5, decussate, orbicular, concave, thick,
persistent, outer pair shorter than inner; petals 4, purple, upto 3 cm long,
orbicular, concave, thick, fleshy; stamens many, 1-2 seriate; filaments 4-5 mm
long, slender, connate at base; anthers ovate-oblong, apex recurved; ovary
superior, globose, smooth, 5-8-locular; ovules solitary, ascending; stigmas
sessile, punctate, 5-8 lobed, lobes cuneiform. Fruit a berry; 5-7 cm across,
glossy purplish-black, smooth, surrounded at base by sepals, apex crowned by
5-8 lobed stigma; pericarp thick, spongy, reddish, with yellow latex; seeds up
to 8, oblong, 1-2 cm long, laterally compressed; aril opaque, very pleasant,
juicy, thick, white.
Uses: Food
Habitat: Cultivated
Distribution: Native of Malaysia, widely cultivated in Tropical Asia
FAMILY: MALVACEAE
5. Hibiscus rosa-sinensis var. rosa-sinensis (L.)
Malayalam Name(s): Ayamparathi, Chembarathi
English name(s): Chinese hibiscus, Chinese rose,
Hibiscus, Rose of China, Shoe flower, Tropical Hibiscus
Description: Shrubs, to 4 m high; stems woody and
glabrous. Leaves alternate, ovate to ovate-lanceolate, truncate or somewhat
tapering at base, serrate, crenate or entire, sometimes dentate towards apex,
acute to acuminate at apex, 5-11 x 3-6 cm, 3-5 nerved at base, glabrous to
sparsely stellate-hairy on nerves beneath; petioles 1.5-4 cm long,
simple-hairy; stipules 36 lanceolate or subulate, 3-11 mm long, glabrous.
Flower axillary, solitary; pedicels 2-8 cm long, jointed above middle, glabrous
or pubescent. Epicalyx lobes 5-8, connate at base, lanceolate, 5- 15 mm long,
sparsely stellate-pubescent. Calyx campanulate, 1-3 cm long; lobes connate to
middle, lanceolate, 1.5-2 cm long, stellate and glandular-pilose outside.
Corolla infundibular, 6- 12 cm across, red, white, pink, yellow or orange
yellow; petals obovate and entire. Staminal column to 5 cm long, exserted
beyond corolla, antheriferous in upper half. Capsules oblong-rounded (rarely
formed).
Uses: Medicinal
Habitat: Grown as ornamental plant
Distribution: Native of Pacific Islands; cultivated in
Tropical and Subtropical countries.
FAMILY: STERICULIACEAE
6. Theobroma cacao L.
Malayalam Name(s): Kokko
English name(s): Cocco, Cacao, Cocoa Tree, Chocolate
Nut tree
Description: Small, evergreen trees. Leaves alternate,
large, elliptic-oblong or obovate, entire, abruptly acuminate, 15-30 cm long,
leathery; short-petioled with a well-marked pulvinus at each end. Flowers
cauliflorous, small. Petals hooded at base. Staminal tube short with 5 petaloid
elongate staminodes and 2 or 3 sessile anthers. Ovary sessile, 5-loculed;
ovules many in each locule; stigma 5-lobed. Fruit a large woody drupe,
ellipsoid-ovoid, ca 30 cm long, smooth or ribbed, reddish yellow, 5-loculed
each with a double row of almond-like seeds embedded in white-pinkish or
brownish mucilaginous aromatic pulp.
Uses: Food, Chocolate
Habitat: Cultivated
Distribution: Widely cultivated in the tropics; native
of Tropical America.
FAMILY: OXALIDACEAE
7. Averrhoa bilimbi L.
Malayalam Name(s): Bilibi, Bilimbi, Chemmeenpuli,
Chimbili, Irumbampuli, Keerichakka, Pulinchi, Vilimbi
English name(s): Bilimbi, Cucumber tree, Tree Sorrel,
Kamias, Belimbing buloh
Description: Tree, to 15 m tall; young parts pale
yellow to rusty-velvety. Leaves usually terminally tufted; rachises 15-55 cm
long; leaflets 5-19 pairs, variable, acute to acuminate at apex, to 12 x 4 cm;
lateral nerves 6-14 pairs. Panicles cauliflorous from tubercles on main trunk
to ground level and on main leafless branches, fascicled and pendulous, to 18
cm long, rarely axillary; solitary and erect; pedicels 4-15 mm long; jointed
near middle. Sepals elliptic to lanceolate or spatulate, acute or obtuse, 3-8 x
1.5-3 mm, sparsely puberulous outside near base, yellowish green to purplish
green. Petals free, lanceolate-spatulate, 10-20 x 3-4 mm, glabrous 40 inside,
dark pink; claw 3-6 mm long. Stamens all fertile; filaments 2-12 mm long,
unequal. Ovary ellipsoid, ca 4 mm long, densely appressed-pale-strigose; ovules
4-7 in each locule; styles to 9 mm long. Fruits cylindric, obtuse, obtusely
angled, to 10 x 5 cm; seeds to 14, 6-7 x 4-6 mm, exarillate.
Uses: Food
Habitat:
Cultivated
Distribution: Native of Malaysia, cultivated in other
Tropical countries.
CONCLUSION
Exotic plants comprise a substantial
portion of the floristic diversity. Exotic plants appear to contribute positive
to some biodiversity functions, but may impact native communities over longer
time frames. There are many are many factors which can affect plant invasions.
Some of them can promote invasions of plants, while other factors can inhibit
invasions. All factors can be divided into internal and external factors. The
effects of exotic species to ecosystems are mainly on the productivity, soil, water,
disturbance, community structure and dynamics. Exotic plants can directly and
indirectly influence natural ecological communities by modifying the structure,
decreasing diversity and altering ecosystem function.
An invasive alien plants is any
species that is not native to that ecosystem and is capable of propagating
itself, whose introduction causes or is likely to cause harm to the
environment, economy, or human health, as well as other species, are affected
by climatic changes. Predicted environmental changes, such as changing in
precipitation and temperature, nutrient availability and soil disturbance, may
enhance the susceptibility of habitats to invasion by non-native plant species.
Many studies have tried to predict future distributions of invasive species
taking different approaches. Since introduced species are more spread in
disturbed ecosystems with reduced competition, it is crucial to consider the
natural and human factors, such as economic activity, urbanization, land use,
overpopulation, migration etc., associated with the occurrence. In general, the
invasion process is a complex series of event, reliant upon both the invasive
capabilities of the species and the invisibility of the ecosystem. Global
environmental changes additionally complicate a continuous battle of
governments and managers to detect and control invasive species.
Comments
Post a Comment