Adaptations of Plants: Morphological, Physiological, and Anatomical Adaptations for Class 10th, 11th, and 12Th
Introduction
The environment has a significant impact on how living things respond to it and how they develop. The organisms develop certain morphological, anatomical, physiological, and reproductive traits to resist challenging environmental conditions and make the best use of the environment’s resources (nutrients and other conditions present therein).
Any characteristic of an organism or one of its components that helps it to endure under the environmental conditions of its habitat is referred to as Adaptation. Every organism grows into its environment, and the same is true of a population or society. A sequence of adaptations with survival value leads to the culmination of an organism’s life cycle or the stabilisation of a community.
Features that prevent the deterioration of an organism’s essential vegetative tissues and aid in the massive creation and effective spread of reproductive bodies are considered adaptations of survival value. Warming (1895) first recognised the impact of regulating or limiting forces on the vegetation in ecology. He divided plants into several ecological groupings based on their needs for water as well as the type of substrate they grew on.
According to the type of substratum (soil), warming divided plants into five groups:
1. Acid-loving plants (Oxylophytes)
2. Plants were grown on salty soil (Halophytes)
3. Grass on the sand with plants (Psammophytes)
4. Plants that grow on the outside of rocks (Lithophytes)
5. Plants that flourish in rock fissures (Chasmophytes).
Since epiphytes do not have a long-term link to the soil, they are not included in the aforementioned group (substratum). Based on how the plants relate to water, Warming divided the plants into two categories in 1909. In actuality, the elements that elicit significant changes in plant shapes and plant life are the water supply to the plants and the control of transpiration.
The plants have been divided into the following groups according to their needs for water and the types of soil they prefer:
1. Hydrophytes: Plants that grow in or close to the water
2. Xerophytes: Plants that have evolved to thrive in environments with extremely limited water availability.
3. Mesophytes: Mesophytes are plants that grow in a medium-to-high humidity environment.
Hydrophytes: Also known as aquatic plants, hydrophytes are plants that thrive in moist environments or water, either partially or completely submerged. Utricularia, Vallisneria, Hydrilla, Chara, Nitella, Lotus,
The aquatic environment offers a matrix for plant growth where temperature variation is at a minimum and nutrients are largely found in a dissolved condition. However, as water bodies get deeper, light and oxygen become lacking. Aquatic vegetation is zoned according to depth as a means of maximising the use of light.
Water movements, ranging from weak currents to small vertical circulation, are present in the aquatic environment. Streams travel in a single direction and frequently in a reversible direction. The vegetation that lives there is frequently abraded by the water currents, therefore several adjustments are needed to endure this abrasive activity. All biological processes are directly impacted by water because it makes up a significant component of plants’ and animals’ bodies (70 to 90% of their cell protoplasm is water).
The amount of available water has an impact on the speed and scope of photosynthesis, respiration, nutrient absorption, growth, and other metabolic activities in plants. Low relative humidity reduces transpiration and interferes with plant growth. On the other hand, plants in areas with high moisture levels exhibit decreased transpiration.
Classification of hydrophytes
The hydrophytes are divided into the following categories based on how they interact with water and air:
(1) Submerged hydrophytes
(2) Floating hydrophytes
(3) Amphibious hydrophytes
(1) Submerged hydrophytes
Submerged hydrophytes are plants that grow below the water’s surface without coming into touch with the atmosphere. Examples include aquatic bacteria as well as the plants Vallisneria, Hydrilla, Potamogeton, Najas, Ceratophyllum, Mynophyllum, Utricularia, Chara, and Nitella.
(2) Floating hydrophytes
Floating hydrophytes are plants that float on top of the water or just below it. Both water and air are in contact with these plants. They might or might not have roots in the ground. The floating plants on this surface have been split into two groups.
(1) Free-floating hydrophytes
Although they are not rooted in the dirt, these plants float freely on the water’s surface. Examples include: Trapa bispinosa, Lymnanthemum, Eichhornia crassipes (water hyacinth; colloquial name: Jalkumbhi), Salvinia (a fern), Wolffia arhiza and Wolffia microscopica (rootless and minute duckweed), and Azolla (a water fern)
(2) Floating but rooted hydrophytes
While the roots of some submerged plants are buried beneath the murky water in ponds, rivers, and lakes, their leaves and blooming branches float on top of the water or just beneath it. They belong to the category of “floating but rooted hydrophytes.” Water lilies, lotuses, Ceratopteris thalictroides (a hydrophytic fern of the Parkariaceae family), and others.
(3) Amphibious hydrophytes
Both the aquatic and terrestrial lifestyles of these plants are suitable for them. In shallow water or on a muddy substrate, amphibious plants can flourish. The term “halophytes” refers to amphibious plants that thrive in saline-marshy environments. These plants may have roots that are submerged in water or sections of their stems and leaves that are buried in the mud, yet some of their foliage, branches and blooming shoots emerge from the water’s surface or may spread across the land.
These amphibious plants exhibit mesophytic or occasionally xerophytic characteristics in their aerial portions, whilst their underwater parts develop full hydrophytic characteristics. Amphibian hydrophytes include several types of rice (Oryza sativa), Marsilea, Sagittaria, Alisma, Jussiaea, Neptuma, Commelina, Polygonum, etc. Some of these plants have roots that are submerged in water-lodged soil or mud, but their shoots are entirely exposed to the air like those of land plants. They’re referred to as marsh plants. Common marsh plant types include Cyperus, Typha, Scirpus, Rumex, etc.
These are listed below:
(a) Temperature of water
(b) Osmotic concentration of water
(c) Toxicity of water
The quantity and type of chemical compounds dissolved in water determine the osmotic concentration and toxicity. The alteration in water’s osmotic content has a significant impact on aquatic plants’ physiology. Due to water’s poor heat conductivity, aquatic plants are exposed to fewer temperature extremes (i.e., it takes a long time its heat and cool). Since there is no chance of plant tissue transpiring, hydrophytes are less impacted by high temperatures.
Adaptive features of hydrophytic
The aquatic environment is consistent throughout, hydrophytes only develop a few adaptive traits. The following headings highlight key traits of these plants:
Morphological Adaptations
Hydrophytes have weakly developed root systems, which is submerged hydrophytes may or may not be branched. The plant body, which is in direct touch with water, acts as an absorptive surface and absorbs water and minerals, rendering the roots useless. This may be the cause of the diminished or nonexistent roots in hydrophytes. Hydrophytes that float have highly underdeveloped root hairs.
Although the roots of floating plants lack genuine root caps, they frequently produce root pockets or root sheaths that serve to shield their tips from harm. However, the precise roles played by these root pockets remain unclear. Even though some rooted hydrophytes, such as Hydrilla, Valhsnena sp., Elodta Canadensis, etc., obtain their nutrients from water through their body surfaces, they nevertheless rely in part on their roots to absorb minerals from the soil.
Some plants, such as Ceratophyllum, Salvinia, Azolla, Utricularia, etc., are completely devoid of roots. Two types of roots, some of which are floating roots that are negatively geotropic and spongy, form in Jussiaea repens when the plants grow on the water’s surface. The plants float thanks to their floating roots.
The stems of aquatic plants are extremely delicate and either green or yellow. It can occasionally be altered to become a runner, rhizome, etc.
Leaves
The leaves of floating plants are often peltate, long, round, light or dark green, thin, and extremely smooth. While their lower surfaces typically come into contact with water, their upper surfaces are open to the air. The petioles of the leaves of the lotus plant exhibit unbounded growth potential and continuously support the leaf laminae on the water’s surface.
Heterophylly
Two distinct leaf kinds can be seen on some aquatic plants. We refer to this phenomenon as heterophylly. Examples, are Sagittaria sagittaefolia, Ranunculus aquatilis, etc. The leaves that float on or above the water’s surface in this occurrence are typically large, round, or somewhat lobed, whereas the leaves that are submerged are typically linear ribbon-shaped or deeply dissected. The following physiological trait behaviour of these aquatic plants is likely linked to the presence of heterophylly.
Quantitative reduction in transpiration
1. The broad leaves on the water’s surface cover the dissected leaves that are submerged and restrict the amount of light that reaches the submerged leaves, which need very low-intensity light.
2. Submerged leaves serve as water-absorbing organs, plants don’t respond very much to drought stress because they don’t need enough water throughout the drought.
3. The diversity of environments and life forms
4. The hydrostatic pressure within the plant body is controlled by broad leaves that are situated on the water’s surface.
5. The smooth, shiny, and frequently wax-coated leaves of free-floating hydrophytes have this characteristic. In addition to shielding the leaves from physical and chemical harm, the wax layer also prevents stomata from becoming blocked by water.
6. Water hyacinth, Trapa, and other floating plants have distinctively inflated, spongy petioles that give them buoyancy.
7. Submerged hydrophytes typically have narrow, tiny leaves. Some plants, such as Myriophyllum, Utricularia, Ceratophyllum, etc., allow for finely dissected leaves. The thin, split-leaf segments’ malleable segments provide little resistance to the water’s currents. Plants experience less mechanical stress and water stress in this way.
8. The leaves of the amphibious hydrophytes exhibit typical mesophytic characteristics and are more durable than the leaves of other hydrophyte groups.
9. Water is used to accomplish fruit and seed pollination and distribution. Fruits and seeds can readily float on the surface of the water since they are low in weight.
10. In hydrophytes, vegetative reproduction is a frequent means of propagation. Either winter buds or the fragmentation of common shoots can do this. Zoospores and other specialised motile or non-motile spores are primarily responsible for reproduction in living things.
Physiological adaptations in hydrophytes
The cell sap of the aquatic plants has a low osmotic concentration and a low compensation point. Cell sap has a similar or slightly greater osmotic content as water. The general plant surface is how the submerged plants acquire nutrients. The surface cells allow the gases to be exchanged from the water. The gases created during respiration and photosynthesis are partially stored in the aerenchyma’s air chambers to be used as and when necessary. The submerged hydrophytes don’t transpire at all. Emergent plants and hydrophytes that float freely, however, transpire excessively quickly. To prevent the plant body from rotting while submerged, mucilage cells and mucilage canals exude mucilage.
Xerophytes
Xerophytes are plants that thrive in xeric or dry environments. Xeric environments are places where the amount of available water is insufficient.
Xeric habitats may be of the following types
Dry habitats (where the water-retaining capacity of the soil is very low and the climate is dry, e.g., desert, rock surface, wasteland, etc.).
Physiologically dry habitats (areas where water is abundant but cannot be readily absorbed by plants). These environments could be very hot, overly cold, or excessively acidic. Habitats become literally and physiologically dry, such as the side of mountains.
Xerophytes are plants that are typically found in the desert and semi-arid environments, but they can also flourish in mesophytic environments when there is enough water available. Extreme dryness, low humidity, and high temperatures are all circumstances that these plants can tolerate.
These plants develop unique structural and physiological traits when growing in unfavourable settings, primarily focusing on the following goals:
(a) absorb as much water from the environment as possible
(b) retain water in their organs for a very long period
(c) limit transpiration rate to a minimum
(d) prevent excessive water consumption.
Xerophytes are divided into several types based on how well they can withstand drought. The following are these groups:
Drought escaping plants
These xerophytes have a brief lifespan. They persist in the form of seeds and fruits with tough and durable pericarps and seed coverings during very dry periods. The seeds sprout into new, tiny plants that finish their life cycles in a matter of weeks when favourable conditions (which are of extremely short duration) appear. Before the dry situation arrives, the seeds reach maturity.
In this approach, harsh weather has no impact on plants. Ephemerals, drought evaders, or drought escapers are terms used to describe them. In semiarid regions with brief rainy seasons, these plants are quite prevalent. Examples include (Papilionatae), a few unassuming Compositae (such as Artemisia), members of the Zygophyllaceae and Boraginaceae families, as well as several types of grass.
Drought enduring plants
These are tiny plants with the ability to withstand or tolerate drought.
Drought resistant plants
These plants acquire specific adaptation traits that enable them to withstand extreme droughts. Various habitats support the growth of xerophytes. Some plants (Lithophytes) thrive in rocky soils, whereas others flourish in deserts, on sand and gravel, or even on waste ground (Eremophytes). While some xeric environment plants do not produce structures for storing water, others do.
Xerophytes on this surface can be categorised into two groups, which are as follows:
1. Succulent xerophytes.
2. Non-succulents, also called true xerophytes.
Succulent xerophytes.
Succulent xerophytes are plants that actively accumulate water inside of certain of their organs, causing them to swell and become fleshy. In other words, the majority of the plant’s body is made up of tissues that store water. When the soil runs out of available water during a severe drought, the water stored in these tissues is used up.
Xerophytic Adaptations
Dry environments encourage the development of specific structural devices in plants. There could be two different forms of these structural changes in xerophytic plants.
1. Xeromorphic characteristics are xerophytic traits that are inherited and genetically fixed. No matter the environment—whether they are growing in humid climes or deserts—they will show up in xerophytes. Despite growing in damp environments, halophytic mangroves and many other evergreen trees always exhibit xeromorphic traits.
2. These characteristics are always connected to dry conditions because they are caused by drought. No one ever inherits them. If all the ideal circumstances are provided for them, these traits might vanish from plants.
Mesophytes
Common terrestrial plants known as mesophytes thrive in conditions that are neither too moist nor too dry. These plants are unable to grow in wet or water-logged soils or dry environments. In other words, mesophytes are the plants that grow in favourable soils and climates. This category includes the vegetation found in forests, meadows, and cultivated fields. The most basic mesophytic community consists of grasses and plants, whereas more complex communities have bushes and trees (rainforests in the tropics).
Types of Mesophytes
1. Communities of grasses and herbs.
(2) Communities of woody plants.
Communities of Grasses and Herbs:
Herbs and grasses, whether annual or perennial, are among them. The grasslands are located in a region with annual rainfall ranging from 25 to 75 cm. Many nations around the world, including the United States, Canada, Australia, Southern Russia, Africa, and India, experience them over sizable interior regions.
Mat-grasslands, mat-herbage, and the Arctic and the Alps These societies are only found in mountaintops and the polar regions. The plants are soft, tiny shrubs, and there are no under-shrubs at all. Lichens do not appear, but mosses may coexist.
This group is subdivided into two:
(a) Mat grassland (Gramineae)
(b) Mat herbage
Meadow
Mesophytes and hydrophytes are connected by this because they both thrive in soils with a moisture content of 60–83 per cent. Plants have tall, stemmed perennial herbs. Due to plant overgrowth, the soil is undetectable. The majority of plants have rhizomes. The leaves are thin, wide, flat, and glabrous, which are mesophytic characteristics. There are several members of the family Gramineae, Ranunculaceae, Papilionatae, and Compositae.
Pasture on cultivated land
In comparison to a meadow, pasture vegetation is shorter and more open. It is frequently disturbed by grazing. Grass, dicot plants, and various mosses are frequently found in the vegetation.
Communities of Woody Plants (Bushland and Forests)
These are classified as follows
Mesophytic bushlands
Such a mesophytic community develops when temperature and other variables are too favourable for herbage vegetation growth yet unfavourable for the growth of forests. There are various locations where xerophytic and mesophytic bushlands converge. The key plants in bushlands include Salix, Arabis, Lathyris, Vicea, etc.
Deciduous forests
These woods can be found in regions with moderate temperatures and sufficient, uniformly distributed rainfall (about 75 to 150 cm per year). Trees in these types of woods lose their leaves for a portion of the year. About five to eight months go by before the foliage disappears. In temperate and frigid climates (where the winters are long) as well as in the tropics (where the summers are long), this phenomenon of repeated foliation and defoliation of trees is common. Dorsiventral leaves have a variety of forms and architectures.
The trees have a lot of branches. There are mycorrhizae on the roots. On the outside of the trees, epiphytic mosses and lichens proliferate in great numbers. The wind pollinates the majority of the plants. The microflora in the soil is quite diverse. The major trees in those specific communities are used to name the deciduous forests, such as Quercus-Oak forest, Betula-Birch forest, FagusBeach forest, and so on.
Tropophytes (changing plants), This group of mesophytes can include the fascinating group of tropical plants known as tropophytes (changing plants). In most tropical places, the weather is rather consistent throughout the year, however, in some tropical areas, the weather alternates between damp and dry, chilly conditions. Plants that grow in the humid, heterogeneous climate of the tropics adapt their structural makeup in some way to withstand the cyclical nature of favourable and unfavourable seasons. In other words, during the rainy season, tropophytes behave like mesophytes, and during the cold, dry season, they act like xerophytes. The onset of winter or the summer are both potential times for leaf shedding.
These plants have three key adaptation traits:
(a) better winter bud protection
(b) thick bark coating on the stem
(c) formation of a subterranean stem that shields perennating buds from severe drought.
Evergreen forests
These forests can be found in the southern hemisphere’s tropical and subtropical areas as well as the cold temperate zones. These woodlands have evergreen plants (i.e., they retain their leaves for more than one year until new foliage appears). In these forests, very few species may exhibit leaf-fall.
Evergreen forests are of three types
Antarctic forests
These woods cover the mountains in New Zealand and a few other nations where the yearly temperature ranges from 5° to 70°C and there is a lot of rainfall all year long. These woods contain important plant species such as conifers, Myrtaceae, and Hymenophylaceae. There might also be liverworts and mosses.
Subtropical forests
These forests can be found in areas with a considerable amount of rainfall but less extreme seasonal temperature variations. Rain rarely falls during the winter. The plants reach a height of nearly 30 metres. Oaks, magnolias, tamarinds, and mosses can all be found in these forests. Eastern U.S.A., South Brazil, South Africa, East Australia, Southern China, and Japan are countries that have subtropical woods.
Tropical Rain forests or Tropical Evergreen forests
Low-lying areas near the equator with an annual rainfall of 180 cm or more are home to tropical rain forests. The term “primitive forest” refers to a form of forest that is the densest and least affected by biotic agents. The world’s peak vegetation is represented by the rain forests. Such a forest’s climate is characterised by:
(1) High humidity (air saturated with 95% humidity)
(2) High temperature
(3) Daily rains
(4) No distinct dry season
(5) Soil is very rich in humus, black in colour, and porous.
The plants have multiple levels and exhibit luxuriant growth. “Forest is stacked atop forest,” as Humboldt so aptly put it, with the tallest trees making up the top layer roughly 40 to 50 metres above, followed by a layer of short trees, a layer of low palms and trees, ferns, and finally a layer of strewn herbs and shrubs (4 to 5 metres in height). Selaginella, mosses, etc.
Rafflesia, Balanophora, Monotrapa, and other plants may have saprophytes and parasites living on their roots. In these woodlands, lianas and epiphytes are highly prevalent. The forests are impenetrable due to the extremely dense growth of bushes and climbers. Plants typically develop into trees. For the stability of their massive trunks, the majority of them grow root buttresses. They exhibit cauliflory, which has stipules, leaf sheaths, petioles, and other protective structures around the buds. Flowers grow high over the heads and come in a variety of colours.
Plants don’t exhibit foliation and flowering cycles. Every species has a unique timing for flowering and foliation. The leaves come in practically any form, and they often face upward to let the excess water drain off. The cutinized and silica-impregnated leaf surface shields the plants from heavy rainfall. There may be channelled nerves and drippy tips on the leaves (i.e., they have long and narrow apices). The bark of trees becomes thick.
Tropical rain forests frequently contain plants from the groups Leguminoceae, Lauraceae, Myrtaceae, Moraceae, etc.
In the tropical rainforest, vegetation succession occurs in the order described below:
The initial colonisers are deciduous plants, which are eventually replaced by semideciduous vegetation that only lasts for a brief time until semievergreen plants arise. Some evergreen plants eventually blend in with the semi-evergreen vegetation and take over. The climax forests grow in this way. Only if the biotic elements are not allowed to significantly impact the vegetation is this sequence of events feasible.
Central and southern America, central Africa, the Pacific Islands, Malaya, and many other equatorial nations all have tropical rain forests. These woods can be found in India on the western slopes of the Nilgiri Mountains, portions of Assam, and the southeast Himalayas. The economic importance of tropical rainforests to people is enormous. High-quality timber is produced by them.