Water is a nessessity substance that all living things cannot do without. It is important for: Temperature regulation, aid digestion, nutrient absorption and waste removal etc. Sources of water could be from rain, ocean, streams, rivers, well, borehole etc.
When there is water shortage, adverse effects will occur on health, the economy, and the environment. Water shortages can lead to waterborne diseases, dehydration, drought, heat exhaustion and heat stress particularly when accompanied with high or extreme temperature etc.
DROUGHT
Drought is a major environmental stress that can negatively impact plant growth and development, and is a significant threat to global food security. It is a prolonged period of dry weather that causes a water shortage. It can happen anywhere in the world and can have serious consequences on people, agriculture, the economy, and the environment. It can be caused by natural factors like weather patterns, or by human activity.
Some natural causes include ocean temperatures like El Niño( A phenomenon that occurs when the sea surface temperatures in the central and eastern Pacific Ocean are warmer than average) and La Niña ( cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, such as winds, pressure and rainfall), Lack of water in stores, Soil moisture levels and climate patterns can cause drought in different parts of the world. For example, low precipitation over an extended period of time can lead to drought. Also, Atmospheric conditions such as climate change, changes in the jet stream, and changes in the local landscape are all factors that contribute to drought occurrence.
Human activities that can cause drought include deforestation, soil degradation, over farming, excessive irrigation, erosion and intensive agriculture.
Droughts can have a serious impact on people, including increasing the risk of disease and death, threatening livelihoods, decreased water quantity and quality, increased mortality rates, and adverse mental health. During drought conditions, fuels for wildfire, such as grasses and trees, can dry out and become more flammable. They can also impact agriculture, causing crop failure and leading to food shortages ( food insecurity).
Droughts can last for weeks, months, or years, and sometimes the effects can last for decades.
TYPES OF DROUGHT
Climatological community has defined four types of drought:
1) Meteorological drought,
2) Hydrological drought,
3) Agricultural drought, and
4) Socioeconomic drought.
1. METEOROLOGICAL DROUGHT: This drought happens when dry weather patterns dominate an area.
2. HYDROLOGICAL DROUGHT: It occurs when low water supply becomes evident, especially in streams, reservoirs, and groundwater levels, usually after many months of meteorological drought.
3. AGRICULTURAL DROUGHT: This type of drought focuses on precipitation shortages, differences between actual and potential evapotranspiration, soil water deficits, reduced groundwater or reservoir levels etc. It happens when crops become affected by dry spell. And
4. SOCIOECONOMIC DROUGHT: Relates the supply and demand of various commodities to drought. It usually occur when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply. For example, drought that result in significantly reduced hydroelectric power production because power no longer do depend on streamflow rather than storage for power generation.
Meteorological drought can begin and end rapidly, while hydrological drought takes much longer to develop and then recover.
CLASSIFICATION OF DROUGHTS
For a better understanding of the causes of drought, droughts can be broadly classified into three main categories. They include;
1. CLASSIFICATION OF DROUGHT BASED ON THE SOURCE OF WATER AVAILABILITY
A. METEOROLOGICAL DROUGHT: This is a Drought caused by lack of rain in a particular region. Based on the percentage of rainfall scarcity, meteorological drought can further be divided into three levels which are:
a. SEVERE DROUGHT: Occurs when rainfall is more than 50% lesser than the normal amount.
b. MODERATE DROUGHT: When rainfall is 26-50% less than normal.
c. SLIGHT DROUGHT: When rainfall is 11 to 25 percent lesser than the normal rainfall in a region.
B. HYDROLOGICAL DROUGHT: This is the type of drought that result from extremely low rainfall which result in the drying up of streams, rivers, lakes, ponds in a particular drought-prone region.
C. AGRICULTURAL DROUGHT: This drought is caused by lack of rain and loss of soil moisture. Agricultural yield becomes damaged and farming practices become very difficult.
2. CLASSIFICATION OF DROUGHT BASED ON THE TIME OF OCCURRENCE
A. SEASONAL DROUGHT: Referred to a prolonged dry period that occurs in climatic areas with distinct wet and dry seasons. These kinds of droughts occur in well-defined dry climates and wet climates too. This can be mainly seen in areas having monsoon types of climate. To overcome this type of drought, farmers do adjust their planting schedules so as to take advantage of the rainy season.
B. PERMANENT DROUGHT: This type of drought occurs in the driest climates, where the vegetation is adapted to aridity and agriculture is only possible with continuous irrigation. Such areas experiencing permanent drought are turned into deserts and the natural vegetation of the place are completely changed and replaced with cactus, Xerophytes, thorny shrubs, etc.
C. CONTINGENT DROUGHT: Many places may experience drought due to irregularity and variation in the amount of rainfall they receive in a particular season. The same areas may experience a lot of rain in the future. Agriculture takes a serious hit due to these droughts.
3. CLASSIFICATION OF DROUGHT BASED ON A MEDIUM
A. SOIL DROUGHT: Result of soil moisture depletion due to droughts.
B. ATMOSPHERIC DROUGHT: Drought is experienced due to certain atmospheric conditions like low humidity, low rainfall, etc.
CHARACTERISTICS OF DROUGHT
Characteristics of drought include impacts, intensity, duration, spatial extent, and timing.
Intensity commonly refers to the severity of the precipitation deficit and how quickly it develops. Magnitude accounts for the combination of a drought’s intensity and duration. Each drought is unique, but common features of the most severe droughts that have far-reaching human and ecological impacts include long duration, large moisture deficits, and large areal extent, particularly when these impacts occur during a climatological wet season
HEAT STRESS
STRESS
Stress is defined as an external factor that exert a disadvantageous influence on plants. Or it can also be defined as an external condition which adversely affect plant growth, metabolism, development and or productivity of the plant.
CLASSIFICATION OF STRESS
There are two classes of stress . They are:
A. STRESS BASED ON THE MEDIUM THAT CAUSES IT
1. Biotic stress
2. Abiotic stress
BIOTIC STESS: This is the type of stress that occur due to interaction between living organisms. Or can be defined as biological insults that a plant may be exposed to like pathogens infection, insects, parasitism or mechanical damage by herbivores.
ABIOTIC STRESS: These are Physical or chemical factors that the environment imposes on a plant, such as temperature, light, drought, flooding, salinity, and heavy metal toxicity. This stress occur as a result of different changes in the environment. This stress can further be divided into various substresses:
a. Water stress: Drought and flood
b. Metal stress which result in deficiencies and toxicity of nutrients
c. Ultraviolet stress
d. Oxygen stress
e. salinity stress
All these stress directly or indirectly result in oxidative stress. Oxidative stress is the stress due to creation of ROS (Reactive oxygen species).
B. STRESS BASED ON LENGHT OF OCCURRENCE
1. Short term stress
2. Long term stress
SHORT TERM STRESS: This type of stress is also called low stress. It is a period of stress that last within minutes to hours. It makes the plant to be more tolerant to stresses especially if they experience a similar stress later in their development. However, if the stress is too strong or chronic, it can cause considerable damage and eventually lead to cell and plant death. This stress can easily be overcome by impaired mechanisms.
LONG TERM STRESS: It is a stress that result from prolonged period of unfavorable conditions that can cause significant damage and eventually lead to plant death. This type of stress causes extreme damage to plants which result in impairable injuries or death of the plant.
Note that Plants can develop stress tolerance mechanisms and adapt to some stress, but long-term stress can overwhelm their repair and coping mechanisms.
STRESS RESISTANT MECHANISMS
1. STRESS RESISTANT PLANTS: This is a plant that is able to tolerate the stress.
2. AVOIDANCE: Avoidance is a plant’s ability to prevent or weaken the effects of a stressor on its cells. It is a resistant mechanism that helps plants escape the damaging effects of environmental stresses. For example, Plants use avoidance strategies to balance water uptake and loss, such as closing stomata to reduce water loss. This mechanism is of two types. Adaptation and Escape
ADAPTATION: Plants have evolved a variety of adaptations to help them resist stress. Adaptation causes permanent changes in the characteristics of the plant that enables the plants to survive. For example; Hydrophytic and Xerophytic Adaptation.
Xerophytic adaptation include: Reduced/rolled culled leaves, thicker waxy cuticles, stomata in pits with hairs, utilize CAM physiology, and lower growth on ground. Examples of adaptation include: Anatomical changes, Physiological and biochemical responses, Molecular responses, Defensive adaptations and Cold acclimation.
ESCAPE: The plant can escape the stress by growing when the conditions are normal and not growing during stress situation. For example, plants growing in specific seasons.
3. ACCLIMATION: Plants can also adapt to environmental changes throughout their lifetime through a process called acclimation. These are the non heritables with temporary physiological modification. It involves the adjustment of the plants in response to changing environmental factors including processes like osmotic adjustment in the plant. It allows plants to cope with the constant variation in their environment. It involves the differential expression of specific genes in response to a particular stress. Plants can develop tolerance, resistance, or avoidance mechanisms to overcome environmental stresses.
Both Adaptation and acclimation results from integrated events occurring at morphological to cellular ( cellular response) to biochemical ( biochemical response) and molecular ( molecular Response) level.
a. CELLULAR RESPONSES: This is a cell’s reaction to environmental signals, which allows plants to adapt to changes in their environment. This include changes in cell cycle, changes in cell division, and changes in cell wall
b. BIOCHEMICAL RESPONSES: These are the changes that occur in a plant’s biochemical processes when it adapts to different environments. This include changes in osmoregulatory compounds such as production of proline and Glycine
c. MOLECULAR RESPONSES: Plants have several molecular responses to environmental changes which including:
Heat stress response, Cold acclimation, perception of stress signals, altered pattern of gene expression etc.
TEMPERATURE/ HEAT STRESS
Plants can adapt to heat stress in two ways:
1. BASAL HEAT TOLERANCE (BHT): The plant’s natural ability to tolerate heat stress
2. ACQUIRED HEAT TOLERANCE (AHT): It is also known as priming or acclimation. This is when the plant acquires the ability to withstand extreme heat .
Heat tolerance is a highly specific trait, and even closely related species may vary significantly in their ability to tolerate heat
CATEGORIES OF TEMPERATURE STRESS
There are two categories of temperature stress:
1. High temperature stress
2. Low temperature stress
HIGH TEMPERATURE STRESS
This is also known as heat stress. It is a major environmental stress that limits plant growth, metabolism and productivity. Plants are unable to survive above 45°C. Although, pollen grains can survive up to 120°C and the seeds can survive up to 70°C. The CAM (crassulacean acid metabolism) plants such as obuntia and Cacti are adapted to high temperature and tolerate up to 65°C.
Plants exposed to high temperature stress suffer from severe and sometimes lethal, adverse effects. The response of plants to high temperature (HT) vary with the degree and duration of HT and the plant type.
EFFECTS OF HIGH TEMPERATURE STRESS
1. During high temperature, the membrane stability reduces due to excess fluidity of lipids in the membrane. thus, there is disruption of membrane and cell compartment.
2. Disruption of water splitting or oxygen evolving system of photosystem 11
3. Both photosynthesis and respiration are inhibited at high temperature
4. Chloroplast enzymes become unstable
5. High temperature can lead to loss of 3-D structure of certain enzyme.
ADAPTATION OF PLANTS TO HIGH TEMPERATURE STRESS
Plants produce structures to adapt to high temperature stress. Such adaptive structures include:
1. Reflective wax on leaf surface
2. Plants produce small leaves dimension
3. Presence of sunken stomata
4. Vertical orientation of leaf
5. Other structures: Plants can have spines instead of leaves, or develop buds and fruit that drop during extreme heat stress.
6. Behavior: Plants can go dormant to avoid growing during the hottest part of the year.
7. Physiological: Plants can alter their metabolism to change cell water and salt content, proteins, and phytohormones.
In response to sudden rise in temperature, plants produce heat shock proteins.
HOW PLANTS RESPOND TO HEAT STRESS
a.. Plants can perceive changes in temperature through sensors in different cellular compartments.
b. Chloroplasts are considered sensors of heat stress because they change the dynamics in response to ROS/redox changes at the cellular level.
C. One of the best known means of responding to potential damage caused by high temperatures is through the synthesis of HSPs.
d. Heat stress in crop plants has also been associated with an increase in antioxidative capacity with the synthesis of various enzymatic and nonenzymatuvq ROS scavenging and detoxification system.
e. short term response include, leaf orientation, transpirational cooling and changes in membrane lipid composition.
MECHANISMS OF HEAT STRESS TOLERANCE IN PLANT
Heat stress can negatively affect plant growth and production by impacting photosynthesis, respiration, water balance, and membrane stability.
a. Heat shock proteins
b. Antioxidant enzymes.
long term morphological adaptations
C. Hormones
d. short term avoidance or acclimation mechanism
e. High temperature tolerance mechanisms
f. thermosensors
a. HEAT SHOCK PROTEINS:
When plants experience heat stress, they increase the production of heat shock proteins (HSPs), which are chaperone proteins that help repair proteins and maintain metabolic processes. The proteins function as molecular chaperones and regulate protein folding, assembling, translocation and degradation. Examples of HSPs include: HSP 100, HSP 90, HSP 70, HSP 60, HSP 40 and small HSPs
b. ANTIOXIDANT ENZYMES
Plants produce enzymes that scavenge reactive oxygen species (ROS), such as superoxide, hydroxyl radicals, and hydrogen peroxide. These enzymes include superoxide dismutases, catalase, monodehydroascorbate reductase, and glutathione reductase.
c. HORMONES
Plants produce hormones, such as brassinosteroids (BRs), Cytokinins (CKs), Ethylene (ET), Abscisic acid (ABA), Salicylic acid (SA),Jasmonic acid (JA), Melatonin and Isoprenoids. , that act as chemical messengers to help plants respond to heat stress.
d. SHORT-TERM RESPONSES
Plants can respond to sudden heat stress with short-term mechanisms, such as changing leaf orientation, transpirational cooling, and altering membrane lipid composition.
e. LONG-TERM ADAPTATIONS
Plants can evolve long-term adaptations to heat stress, such as changing leaf orientation, transpirational cooling, or altering membrane lipid composition.
f. THERMOSENSORS
Thermosensors are proteins that detect elevated temperatures and alter their structure or activity to signal the cell. They are activated directly by heat and do not require upstream signaling components. They may be made up of DNA, RNA, protein, or lipids. Examples of thermosensors include: Unfolded protein sensors, Phychrome B (phyB), TWA1, and TT3.1 etc.
HEAT STRESS AVIODANCE MECHANISM
Plants uses a number of mechanisms to avoid heat stress. Such mechanisms include: Short-term avoidance
(Plants can change their leaf orientation, reduce water loss by closing stomata, and alter their membrane lipid), Early maturation, Reducing solar radiation, larger xylem vessels, and cooling through transpiration, compositions etc.
HEAT STRESS TOLERANCE MECHANISM
Some major tolerance mechanisms include:
a. Heat shock rotein
b. ion transporters
c. late embryogenesis abundant ( LEA) proteins
d. osmoprotectants
e. antioxidant defence, and factors involved in signaling cascades and
f. transcriptional control
g. Gene expression
All these are essential significant to counteract the stress effect.
a. HEAT SHOCK PROTEINS (HSPs): HSPs are expressed when plants sense heat shock, and they reduce protein misfolding and aggregation.
b. Ion TRANSPORTERS: These help offset biochemical and physiological changes caused by stress.
c. ANTIOXIDANT ENZYMES: These enzymes detoxify reactive oxygen species (ROS) like hydrogen peroxide, hydroxyl radicals, and superoxide. They are found in every cell of all plant types. The enzymes include :
Superoxide dismutase (SOD) -( removes superoxide radicals by converting them to hydrogen peroxide and oxygen ), Catalase (CAT)- ( removes hydrogen peroxide by converting it to water and oxygen ), Peroxidase (POX)- (Scavenges hydrogen peroxide in the extracellular space ), Glutathione peroxidase (GPX) -(Reduces hydrogen peroxide and hydroxyl radicals to water and lipid alcohols ) and others include Glutathione reductase (GR) and Ascorbate peroxidase (APX) etc.
d. OSMOPROTECTANTS: These are small, organic molecules that help plants survive extreme osmotic stress. They are found in the cytoplasm and can help plants tolerate heat stress. They include proline, glycine betaine, and trehalose.
e. HORMONES: These include abscisic acid, gibberellic acids, jasmonic acids, brassinosterioids, and salicylic acid.
f. CELL MEMBRANE STABILITY: Cell Membrane Stability is the most important physiological parameter often used as a screening tool for heat tolerance. Plants maintain cell membrane stability to resist heat stress. When plants are exposed to heat, the cell membrane can become damaged, which can lead to a number of issues such as ion leakage, increased permeability, enzyme inactivation and protein denaturation etc.
g. GENE EXPRESSION: Heat stress changes the expression of genes that protect plants from heat stress. These genes code for proteins that detoxify, transport, and regulate osmotic balance. Some of the gene expression mechanism include : Heat shock transcription factors (HSTFs) and heat shock proteins (HSPs), Hormone-related genes like MYB, EIN3, LOX2, AOC, OPR3 and JMT, Epigenetic regulation, and Genes involved in raffinose biosynthesis.
ANTIOXIDANT DEFFENS IN RESPONSE TO HEAT -INDUCED OXIDATIVE STRESS
It has been observed that catalase (CAT) , ascorbate peroxide (APX) and superoxide dismutase (SOD) showed an initial increase in activities before declining at 50°C, while peroxide (POX) and glutathione reductase (GR) activities decline at all temperatures ranging from 20 to 50°C. In general, total antioxidant activities is at a maximum at 35 to 40°C in the tolerant varieties and at 30°C in the susceptible ones.
MECHANISM OF SIGNAL TRANSDUCTION AND DEVELOPMENT OF HEAT TOLERANCE
. To generate response in specific cellular compartments or tissue against a certain stimuli, interaction of cofactor and signaling molecules are required.
. Signaling molecules are involved in activation of stress responsive genes. There are various signaling transduction molecules related to stress responsive gene activation
. some broad group of those are the Ca-dependent protein kinase (CDPKs) , mitogen-activated protein kinase (MAPK/MPKs) , No, sugar, phytohormones.
. These molecules together with transcriptional factors activate stress responsive genes.
MOLECULAR AND BIOTECHNOLOGICAL STRATEGIES FOR DEVELOPMENT OF HEAT STRESS TOLERANCE IN PLANTS.
HEAT SHOCK PROTEINS
In response to sudden rise in temperature, plants produces proteins called heat shock proteins(HSPs). The proteins are of different sizes depending on the rise in temperature. The proteins can be expressed during heat, cold, salinity and pathogen stresses.
FUNCTIONS OF THE PROTEINS
1. CELL PROTECTION: HSPs help cells survive stressful conditions, such as infection or inflammation. Thus, protect cells from severe damage
2. THERMOTOLERANT: They protect cells from high temperature called thermotolerance
3. PROTEIN FOLDING: Interact with other proteins to create a folding of proteins
and prevent them from aggregating.
4. PROTEIN DEGRADATION: HSPs carry old proteins to the proteasome for recycling. 5. Immune system: HSPs play a role in the immune system, including antigen presentation and tumor immunosurveillance.
5. STRESS TOLERANCE: HSPs help plants tolerate biotic and abiotic stress.
6. REACTIVE OXYGEN SPECIES: HSPs detoxify reactive oxygen species (ROS) by regulating antioxidant enzymes.
TYPES OF HEAT SHOCK PROTEINS
In plants, Heat Shock Proteins (HSPs) can be grouped into five different families
1. HSP100 (or ClpB)
2. HSP90
3. HSP70 (or Dnak)
4. HSP60 (or GroE) and
5. HSP 20 ( or small HSP, sHSP)
The HSP 70 and HSP60 proteins are among the most highly conserved proteins in nature, consistent with a fundamental role in response to heat stress.
LOW TEMPERATURE STRESS
Low temperature stress can negatively impact plant life. Some of these impacted areas include: cell survival, cell division, photosynthesis, water transport, growth, development, and reproduction.
Some of the events used by plants to help them tolerate low temperatures, including: Gene expression changes, Activation of the ROS scavenging system, and Biochemical and physiological modifications.
TYPES OF LOW TEMPERATURE HEAT STRESS
There are two types of low temperature stress.
a. Chilling
b. Freezing
CHILLING: When the temperature is low for normal growth but not low enough to form ice. The temperatures between 0–15°C can injure plants without forming ice crystals. Chilling temperatures can vary depending on the plant’s tolerance and the air temperature and wind speed.
EFFECT OF CHILLING
1. Slow growth
2. Discolouration or necrosis of tissues
3. Germination: Chilling stress can severely impair germination and seedling vigor.
4. Leaf development: Chilling stress can delay leaf development and cause necrotic lesions on leaves.
5. Flowering: Chilling stress can delay flowering and disturb pollen and gametophyte development.
6. Loss of membrane function
7. Decrease in photosynthesis: Chilling stress can inhibit a plant’s photosynthetic capacity.
7. In chilling sensitive plants, the saturated lipids is higher which tends to solidify at low temperature leading to membrane damage.
8. Reactive oxygen species: Chilling stress increases reactive oxygen species (ROS) in plant metabolic pathways.
9. Chlorophyll decomposition: Chilling stress can accelerate chlorophyll decomposition in leaves.
PROTECTION: exposure to cool but non freezing temperature.
FREEZING:
Temperatures below 0°C that cause ice to form within plant tissues.
EFFECT OF FREEZING
1. Ice formation in intercellular spaces resulting in cellular water movement towards ice.
2. Shrinkage of protoplasm
3. Destruction of chlorophyll
4. Change in membrane potential
5. Reduced growth: Freezing stress can restrict plant growth and development.
6. Reduced yield: Freezing stress can reduce crop yield, especially during the reproductive phase of the plant life cycle.
7. Delayed maturity: Freezing stress can delay the maturity of crops.
PROTECTION STRATEGIES
Anti-freezing proteins/thermal hysteresis proteins (THPs). They bind to ice surface preventing their growth
SOME DROUGHT TOLERANT AND PLANTS TOLERANT TO HEAT STRESS
1. AGAVE (Agave americana): This plant is also called century plant. The specie is a monocot native to the arid regions of the Americas. It is primarily known for its succulent and xerophytic species that typically form large rosettes of strong, fleshy leaves and they resemble pineapple leaves. Most agaves are monocarpic, meaning that they die after flowering. They possess shallow roots which they use to absorb any drop of water in the soil. Their flowers are spiked
2. PRICKLY PEAR( OPUNTIA): Prickly pear cactus, is a genus of flowering plants in the cactus family Cactaceae. They are known for their flavorful fruit and showy flowers. They are well-adapted to aridity This Cacti specie produce white, yellow or red flowers. They possess waxy skin that protect then from the sun. They also produce fruits. They possess high water storage capacity in their leaves which is spineous and can survive in USDA planting zones.
3. MOSS ROSE ( Portulaca grandiflora): This is a succulent flowering plant in the purslane family Portulacaceae, native to southern Brazil, Argentina, and Uruguay and often cultivated in gardens. It has many common names, including rose moss, eleven o’clock, Mexican rose, moss rose, sun rose, table rose, rock rose, and moss-rose purslane. It is a popular bedding plant. It possess beautiful bloom of flowers which are purple, yellow and red in colour. They have thick fleshy leaves that make them survive in places where other plants do not survive. In most conditions, they disperse seeds on their own which gives reasons for their wide spread in nature.
4. LAVANDER (Lavandula spica): The common name is lavender, a Drought tolerant plant especially when established. They provide great aroma that helps cleans the mind and body. They are drought tolerant when they get pass their first year and become hardy. They can also survive in USDA growing zones. They produce stunning blue purple flowers with silvery aromatic leaves.
5. TRUMPET VINE ( Campsis radicans) : The trumpet vine,is also called several names such as yellow trumpet vine or trumpet creeper (also known in North America as cow-itch vine or hummingbird vine), is a species of flowering plant in the trumpet vine family Bignoniaceae, native to eastern North America, and naturalized elsewhere. It grows up to 10 metres (33 feet), it is a vigorous, deciduous woody vine, notable for its showy trumpet-shaped flowers which are orange in coloure. They grow quickly and need to be occasionally cut back. Under shoddy areas, they will do well. Once established, they do not need much water.
6. HEN AND CHICKS ( SEMPERVIVUM): Hen and chicken is a common name for several unrelated groups of plants. The name refers to the tendency of certain of these species to reproduce vegetatively by means of plantlets. These tiny plants are produced by the mother plant, and take root on touching the ground. They are rossetts that grow close to the ground and in crevices. They can survive in poor soils with low drainage.
Some of the general include Sempervivum , Echeveria and Jovibarba,
7. CREEPING THYME (Thymus serpyllum): This plant is also known by different common names such as: Breckland thyme, Breckland wild thyme, wild thyme, creeping thyme, or elfin thyme. It is a species of flowering plant in the mint family Lamiaceae, native to most of Europe and North Africa. It is a low, usually prostrate subshrub growing to 2 cm (1 in) tall with creeping stems up to 10 cm (4 in) long. The oval evergreen leaves are 3–8 mm long. The strongly scented flowers are either lilac, pink-purple, magenta, or a rare white, all 4–6 mm long and produced in clusters. They are native to drought and hot condition areas. For example, meditanaerian. They produce green foliage and resembles a carpet afar. They are good for stone pathways and produce beautiful aroma.
8. BOUGAINVILLEA: Bougainvillea is a flowering plants, native to South America, and in the Nyctaginaceae family. They are woody vines with a scrambling habit. It is an excellent choice for drought, heat and saline areas. It produce red, pinch yellow, purple or creamy coloured flowers. They prefer warm, dry and well drained soil conditions and love heat.
9. BLANKET FLOWERS: They are called flamedazers because they produce a flower with red interior and yellow petal round it that resembles a flame. They can also be of any shade of yellow, orange, red, purplish, brown, white, or bicolored. They are found in wild and some tamed to grow in home gardens. They are annual or perennial herbs or subshrubs, sometimes with rhizomes. The stem is usually branching and erect to a maximum height around 80 centimeters (31.5 inches). They do well in full sun and poor soils.
10. CALIFONIA LILAC ( Ceanothus spp) : This is a nitrogen-fixing shrubs and small tree in the buckthorn family (Rhamnaceae). It has several common names in the genus such as buckbrush, California lilac, soap bush, or just ceanothus. This plant produce small dark green leaves with light blue or white flowers. They do not need water under hot weather conditions.
