Ecological groups

ECOLOGICAL GROUPS‘Groups of plants growing under the same set of environmental factors constitute ecological groups’

In 1895 warming classified plants into ecological groupsOn the basis of ;Type of substratumAdaptic factors of the soil

Ecological groups of plants

Hydrophytes Xerophytes Epiphytes Halophytes

HYDROPHYTES

HYDROPHYTES

• Grow in water or in soil which is saturated with water

• Water may be fresh or saline• Lakes ,ponds,pools,rivers,etc. Constitute fresh

water bodies• Phytoplanktons ;non vascular hydrophytes• Vascular hydrophytes may arranged to 3

natural groups they are,

1. Rooted and Submerged plants

• Anchored (rooted) hydrophytes• Completely submerged in water• Restricted to shallow areas where

they get adequate supply of light

They are of two types1.Plants with long stemsThey bear small leaves at the nodes

hydrilla ceratophyllum

potamogetoa

2.Plants with tuberous stemThey bear cauline leaves .the leaves are thin and ribbon shaped.

Vallisneria nymphaea

2.FLOTING PLANTSThey are of two typesFree floating forms• Not attached to the soil• Floating• Grow in large numbers• Some forms have very large leaves and rise

above water eg.water hyacinth

•Some smaller forms are

Pistia salvinia

azolla

•Plants like utricularia normally remain just below the surface of water and are rootless

Floating but rooted forms• Rooted in mud• Possess floating leaves• Grow in shallow regions

Water lilly lotus(nelumsium)

Victoria regia

3.AMPHIBIOUS PLANTS

• Inhibits shallow water• Form the marshy or shallow vegetation• The basal part is submerged in water and

shoots extends well above the soil

typha sagittaria

hydrophylla

ADAPTATIONS OF HYDROPHYTES

• Roots are reduced in size,unbranched and without root hairs

• Stem is thin and delicate due to the lack of mechanical tissues

• Leaves are reduced in size and are thin,linear,or ribbon like to escape the effects of strong water currents

1.SUBMERGED PLANTSMORPHOLOGICAL ADAPTATIONS

Hydrilla with small leaves,small roots,and tuberous stem

ANATOMICAL ADAPTATIONS• They lack cuticle or suberin• Conducting elements are very few and non

lignified• Large number of air cavities for gas exchange

and storage• Mesophyll is undifferentiated to palisade and

spongy tissue• It is mostly of spongy type• Chloroplasts are present in the epidermal cells

•Stomata is absent or non functional•Absence of sclernchyma and collenchyma

2.FREE FLOATING PLANTS

• Extremely reduced roots• Root hairs are absent,special structures known

as root pockets are present insted of root caps

MORPHOLOGICAL ADAPTATIONS

Azolla plant with extremely reduced roots

• Roots are absent in wolffia,utricularia,ceratophyllum etc.

• Stem is extremely reduced but leaves are quite well developed

Water hycinth with small roots but well developed leaves

ANATOMICAL ADAPTATIONS

• Well developed air cavities are present in stems ,leaves, and roots

• Collenchyma and sclerenchyma are completely absent

• Vascular tissues are poorly developed• Stomata are present at the upper surface of

leaves• Palisade parenchyma is developed towards

the upper surface

FLOATING BUT ROOTED PLANTS

• Poorly developed roots• Roots are produced from horizondal stems,

rootstocks or tubers• Elongated and well developed petiole

MORPHOLOGICAL ADAPTATIONS

Well developed petioles

ANATOMICAL ADAPTATIONS• Well developed air cavities are present in

petioles• Leaves are covered with wax• Stomata are present on the upper surfaces of

leaves• Palisade parenchyma is developed but the

spongy parenchyma is in far excess. the later enclose large air cavities

• Mechanical and vascular tissues are extremely reduced

3.AMPHIBIOUS PLANTS

• Well developed root system• Plants have rhizomes which lie in the mud and

may show hydric and xeric adaptations • Heterophylly(presence of more than one type

of leaves) is exhibited, submerged leaves are normally disected and the lobes are linear and thin

MORPHOLOGICAL ADAPTATIONS

ANATOMICAL ADAPTATIONS

• Aerenchyma and storage parenchyma are present

• Mechanical and conducting elements are present

• Thick walled endodermis to check loss of water

• Large air chambers are present. which are separated by diaphragms

XEROPHYTES

XEROPHYTES

• Plants which grows in xeric habitat such as * places like deserts, plain peaks, sand hills * shortage of water *high rate of transpiration• they are modified to withstand unfavourable

conditions

Classification of xerophytes

• Depending upon the ability of xerophytes to withstand unfavourable situation they are classified as;

1.drought escaping 2.drought evading 3.drought enduring 4.drought resisting

1.Drought escaping (ephemerals)

• They are annuals• Very short growing and flowering season• Complete their life cycle in 4-6 weeks• Found growing in semi arid region having

a brief rainy season

Arabidopis thaliana Alyassum alyssoides

2.Drought evading

• Very small in size• Have restricted growth and require very

low amount of water for growth and development

• They conserve whatever little amount if light they get and evade drought

Ambrosia dumosa Encelia farinosa(white bursage) (brittle bush)

3.Drought enduring(non-succulents)

• Slow growing shrubs• They are small and have stunted growth• They endure long dry periods when there is

acute shortage of water• Extremely restricted growth• Leaves wilt and fall down during unfavourable

season• Resume growth in turn of favourable growth

Larrea tridentata (creosote bush)

4.Drought resisting(succulents)

• They have thick and fleshy stems or leaves• They store large amount of water and resist

drought• Have well extended root system for water

absorption• With the help of stored water they continue

their growth, flowering and fruiting

Agave Aloe

Euphorbia opuntia

MORPHOLOGICAL ADAPTATIONS• They are provided with

a very deep and extensive root system for water absorption. it is almost 129 feet below the soil

• The stem is stunted in growth and form a bushy appearance

• Presence of underground stems to tide over the dry season eg.saccharum

• Presence of hard and woody stems eg.acacia,prosopis,zizyphus

• Capparis aphylla have completely dispensed with leaves to check transpiration Prosopis with woody

appearance

• Leaves are reduced to small scaly or spiny structures eg.ruscus,asparagus,casaurina

• Microphyllus leaves are present in many xerophytes

• Plants like nerium have shining surfaces to reflect away light and heat

Asparagus

• The leaves of many xerophytic plants have a waxy coating on the upper surface. they are also covered with a dense mass of hairs

ANATOMICAL ADAPTATIONS• Presence of thick cuticle on the upper and

lower surface of leaves• Thick epidermal walls• Presence of multiple epidermis on leaves

eg.nerium• Stomata are greatly reduced in number and is

restricted to lower surface • Stomata are situated in deep pits and those• pits are filled with hairs eg.nerium

• Sclerenchymatous hypodermis eg.pinus needle

• The spongy parenchyma cells are comparatively fewer and have very small inter cellular spaces

• Presence of small cells and small vacuoles to maintain protoplasmic stability

• The protoplasam is not easily pulled away from the cellwall and therefore the plasmodesmata do not get ruptured

• Well developed xylem and phloem

Physiological adaptations• Thick cell sap

HALOPHYTES

• Inhabit in saline soils• Tolerant to a high concentration of soluble

inorganic salts• The plants are affected by these dissolved

inorganic salts• The effect may be partially osmotic and

partially chemical• To maintain turgidity cell sap is much more

concentrated

SALIENT FEATURES OF HALOPHYTES

• A vast number of halophytic flora are succulents

• Leaves may be thin ,small leathery, and spiny to minimise loss of water in transpiration

• They have evergreen leaves which have water storage tissue, prominent palisade cells, and thick cuticle

• They are provided with negatively geotropic pneumatophores for gaseous exchange eg.mangrooves

• Some halophytes exhibit vivipary ie,seeds germinate before the fruits break off the plants

• Salt glands are presesnt

TYPES OF HALOPHYTES

• They grow on rocks near the rocks

1.LITHOPHILOUS

2.PSAMMOPHILOUS

•They grow on sandy region

3.PELOPHILOUSThey grow in places where the saaline soilloam with a predominance of clay

4.SALT SWAMP AND SALT DESERT• They grow in calm water and muddy spots

5.MANGROVES• Mangroves or littoral swamp forest grow on

sea shores in tropical and sub tropical regions

MANGROOVES

• In tropical and subtropical regions halophytes form a typical sea shore vegetation called mangrooves

• Mangroves are present in suderbans,on the coasts of Mumbai and Kerala,

• Their osmotic potential is maintained at a low level to facilitate absorption of water from sea

MANGROOVES IN KERALA• In Kerala mangroves are distributed in all the

districts except Idukki, Pathanamthitta, Palakkad and Wayanad.

• Maximum extent is reported from Kannur district.

• The total extent of mangrove forests in the state is estimated to be less than 50km2 (Mohanan 1997) .

MAIN SPECIES• Acanthus cillicifolius, • Acrostichum aurem,• Aegiceras corniculatum, • Avicennia officinalis,• Azima tetracantha,• Bruguiera gymnorrhiza,• B. cylindrica, • B sexangula, • Excoecaria agallocha, • E indica,• Kandelia candel,• Rhizophora apiculate, • R mucronata,• Sonneratia caseolaris,• Calophyllum etc.

ADAPTIC FEATURES OF MANGROOVES

• STILT ROOTS • PNEUMATOPHORES :special negatively

geotropical roots for absorbing atmospheric oxygen

• VIVIPARY :seeds start germinating while fruit is still attached to the mother plant

• SHRUBY AND WOODY NATUER• SALT GLANDS; salt glands are present

EPIPHYTES

EPIPHYTES• Plants which grow on other plants• But will prepare their on food unlike parasites• Grow in places where there is regular rainfall

and plenty of humidity in the atmosphere• They bears three types of roots,clinging

roots,velamen roots,and areal roots• They produce large amount of seeds

ADAPTATIONS TO CHEK TRANSPIRATION

• Few leaves• Thick leathery or

succulent leaves• Thick cuticle• Sunken stomata

Classification of epiphytes

• A number of species of family Asclepiadaceae,Pepromia,and a few ferns drive their nutrition from the host and atmosphere

1.Proto epiphyte

2.Hemi epiphyte•Their epyphytism is linked to their early developmental stages which they complete on certain hosts

•Later they grow on ground with their on roots and behave as completely independent plants•Eg.ficus,fig trees etc.

3.Nest epiphyteMany orchids form net like structures to collect large quantities of humus and water

4.Tank epiphyte•The leaves are modified to pocket,funnel,or spoon like structures to absorb humus and mineral nutrients which accumulate in the bark surface crevices of the host support.• Peltate scaly hairs present on the base of the leaves to absorb nutrients•The root as are concerned only with the anchorage of the epiphyte on the host

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