Hydrophytes and xerophytes

1. Anatomical adaptations
🌿 HYDROPHYTES- Hydrophytes are the plants which live completely
or partially submerged in fresh water.Such plants donot face any
problem of water shortage.

2. There are some types of hydrophytes:
Submerged plants:
🍂 Plants which grow below the
water surface and not in contact
with atmosphere and are not
rooted in mud are called as free
floating submerged hydrophytes.
Example-Utricularia etc.
🍂Few plants are submerged but
are rooted in mud.
Example- Hydrilla etc.
Amphibious plants:
🍂These plants grow in shallow
water.Their roots ,some parts of
stem and leaves are submerged in
water. But some flowering shoots
spring well above the water
surface. These plants are adapted
to both aquatic and terrestrial
modes of life’s .
🍂 Example- Limnophylla, Typha.

3. Floating leaves plants:
🍂Free floating-These plants float
freely on the surface of water but
are not rooted in soil. These plants
are in contact with water and air.
🍂 Example- Eichhornia, Pistia,
🍂Rooted- Floating but are rooted in
mud,their leaves and flowering
shoots float on water surface.
🍂Example- Nelumbium, Marsilea.

4. Lets have a detail study of anatomy of hydrophytic
plants(in different- different parts):
🌼 EPIDERMIS: In aqautic plants the epidermis is not for protection but
absorbs gases and nutrients directly from water. The epidermis in
typical hydrophte has an extremely thin cuticle and thin cellulose walls
permit ready absorption from surrounding water. Commonly the
chloroplasts are found in the epidermal cells of leaves, specially when
leaves are thin,these chloroplast utilize the weak light under water for
photosynthesis. In submerged plants stomata are not present and the
exchange of gases is directly done by cell walls. The floating aqautic
plants have abundant stomata on the upper surface.

6. 🌼LACK OF SCLERENCHYMA:
Submerged plants usually have
few or no sclerenchyma tissue.
The water itself gives support to
the plant and protect it to some
extent from injury. The thick walls
of tissues,their density and
presence of collenchyma in some
plants gives some rigidity.

7. 🌼 MINIMUM DEVELOPMENT OF VASCULAR TUSSUE : In vascular
tissues,the xylem shows the greatest reduction and in many aquatic
plants consists of few elements even in stele and main vascular
bundles. In some aqautic palnt’s the stele and largebbundlesnand
frequently in small bundles xylem elements are lacking. In these plants
there is well developed xylem lacuna in position of xylem. The lacuna
resembles typically air chambers. In aquatic plants the phloem is fairly
well developed as compared to xylem. The endodermis is present
around the stele,but it’s also weekly developed.

8. 🌼 REDUCTION OF ABSORBING TUSSUE: The root system in
hydrophytes is feebly developed and root hairs and root cap are
absent. In some aquatic floating plants such as Utricularia,
Ceratophyllum etc.no roots are developed and in submerged plants
such as Vallisneria , Hydrilla etc. Water dissolved minerals and gases are
absorbed by their whole surface. In hydrophytes the root system is
cheifly as holdfast or anchors and a large part of absorption takes place
by the leaves and stems.

9. #Minimum developed vascular tissues. # Reduction of absorbing tissue.

10. 🌼 DEVELOPMENT OF AIR CHAMBERS: Chambers and passages filled with
gases are commonly found in the leaves and stems of hydrophytes. The air
chambers are large usually regular, intercellular spaces extending the leaf
and often for a long distances through stem. The spaces are usually
separated by partition of photosynthetic tissue only one or two cells thick.
The chambers prepare an internal atmosphere for the plant. These air
chambers on the one hand gives buoyancy to the plant for floating and on
one other hand they serve to store up air( oxygen and carbon dioxide). The
carbon dioxide that is given off in respiration is stored in these cavities for
photosynthesis and again the oxygen that is given off in photosynthesis
during day is stored for respiration. The cross partition of air passages is
called as diaphragm, prevent folding. The diaphragms are provided with
minute perforations through which gases but not water can pass.

11. Another specialized tissue frequently
found in aquatic plants that gives
buoyancy to the plant s parts is
arenchyma. The presence of
arenchyma is the characteristic
feature of Decodon, Lythrum
species.However term arenchyma is
applied to any tissue with many
intercellular spaces but such
arenchyma is quite distinct from
typical arenchyma.

12. 🌿XEROPHYTES:
🍂 These plants grow in deserts or in
very dry places,they can withstand a
prolonged period of drought. The
xerophtic plants have to guard against
the excessive evaporation of water,this
do by reducing the evaporating surface.
Plants produce a long tap root which
goes deep into the soil in search of
moisture. To retain water,leaves and
stems become thick and fleshy,this is
further facilitated by abundance of
mucilage.Multiple epidermis may
develop in leaf sometimes.

13. The characteristic anatomical features of xerophytes are as following:
🌼 EPIDERMIS AND THICK CUTICLE: Heavy cutilarisation and extreme
cutinization of the epidermis and even sub epidermal cells are common
in xerophytes. The thickness of cuticle shows various gradations. In
certain cases the thickness of cuticle is only slightly greater than
normal, like that of plant’s semixerophytic habitats. In extreme
xerophytes the cuticle may be thick even more than diameter of
epidermal cells. In addition to presence of thick cuticle,the epidermal
cells become cutinized. Along with well developed cutinized layers the
epidermal and sub-epidermal cells also become lignified. In certain
cases the covering of wax is formed on the epidermis. The epidermal
cells are usually radiated elongated. In leaves of Nerium and Ficus the
epidermis becomes multilayered.

14. 🌼HAIRS: In many xerophtic plants
especially plants in strong wind
prone areas a covering of matted
epidermal hairs on the underside of
leaves prevents water loss. Hairs may
be abundant all over the aerial plant
parts. The thick matting of hairs also
prevents rapid evaporation. The
xerophytes that posses abundant
hairs ,on Thier leaves and stems are
commonly known as trichophyllous.
🌼 SCLERENCHYMA: The xerophytes
commonly have a larger portion of
sclerenchyma in their leaf structure.
The sclerenchyma is found in groups
or in continuous sheets(in Banksia
continuous sheet is present b/w
hypodermis mesophyll).The sheets of
sclerenchyma check excessive
transpiration to some extent and
also gives mechanical strength to
plant body. The xerophytes that
posses heavy sclerification of leaves
are known as sclerophyllous. There is
also abundant pallisade parenchyma
and is compactly arranged.

15. #Sclerenchyma:

16. 🌼 STRUCTURE OF STROMATA: The stomata are very minute openings
formed in the epidermal layer in green aerial parts of plants. The
stomata are essential for intake of carbondioxide and oxygen and for
inward and outward passage of other gases. The evaporation of surplus
water takes place through stomata. The xerophytes may posses less
stomata,either by reduction of leaf surface or of stomatal number per
unit area to reduce excessive transpiration,the stomata that remain
sunken in pits are formed and hence called as sunken stomata. Usually
the depressions contain hairs in them which protect the stomata from
direct attack of wind.

17. #Stomata:. #Epidermis:

18. 🌼ROLLING OF LEAVES: The leaves of many xerophtic grasses,roll tightly
under dry conditions. In grasses the stomata are confined to the central
surface of the leaf,so that when leaf edges roll inward, the stomata are
effectively shut away from the outside air. As the stomata are located
on inner surface of the leaf, the air enclosed by rolled leaf soon
becomes saturated with water under outward water diffusion stops.In
Ammophila arenaria there is tight upward folding of leaf reducing the
air movement over stomatal areas. Special motor cells (hinge) on the
upper surface of leaf are responsible for the inward rolling of leaves. In
xerophtic plants the motor cells are well developed.

19. #Rolling of leaves:

20. 🌼 REDUCED LEAF SURFACE : In
many xerophytes the reduction of
leaf surface prevents the water loss
because the total exposed surface of
plant body is relatively small as
compared to that of normal
mesophytes. In such xerophytes the
leaves are either scale like or very
small size. In such plants the
photosynthesis takes place by stem.
Xerophytes with reduced leaves are
called as microphyllous.
🌼WATER STORAGE TISSUE: Many
fleshy xerophytes posses water
storage tissues and mucilaginous
substance in them. In leaves such
tissue are located beneath the upper
epidermis or upon both sides of leaf.
Storage cells are often large sized
and thin walled. The storage tissue
actually serve as reserve source of
water during drought. The
xerophytes that posses fleshy leaves
or stems are known as
malcophyllous.

21. #Reduced leaf surface: # Water storage tissue:

22. 🌼LATEX TUBES: In many
xerophytic stems and leaves the
laticiferous canals are present
(Euphorbia, Calotropis). Due to
viscosity of latex the transpiration
is reduced to some extent.