Aim: Study of morphological and anatomical Adaptations in Hydrophytes
Hydrophytes are the plants which grow in habitats where water is abundant. They are further
divided into the following six groups.
1. Free floating: These plants float freely and independently on water surface; e.g., Eichhornia,
Lemna, Pistia etc.
2. Floating and possessing roots: These plants float on the surface of water. These plants attach
themselves to the bottom with the help of their roots; e.g., Nymphaea, Trapa etc.
3. Submerged: These plants occur below the water surface, but they do not attach themselves
to the bottom; e.g., Ceratophyllum, Najas etc.
4. Submerged and possessing roots: These plants occur below the water surface and also remain
attached to the bottom of water reservoir; e.g., Hydrilla, Vallisneria etc.
5. Ambhibious and possessing roots: These plants grow in waterlogged soils. Examples are,
Polygonum, Marsilea etc.
6. Emergent and possessing roots: These plants grow in shallow waters and remain attached
to the bottom. A part of the plant is below the water surface and a part above it. Examples are,
Cyperus, Typha etc.
Morphology of Hydrophytes
Hydrophytes have some special adaptations. Following are some of the external features.
Roots: In hydrophytes roots do not play an important role in water absorption. 1. Roots are
either completely absent (e.g., Ceratophyllum) or poorly developed (e.g., Hydrilla).
2. Root pockets are present instead of root caps (e.g., Eichhornia, Lemna, Pistia etc.).
3. Some plants develop floating roots in addition to normal adventitious roots (e.g., Jussiaea
repens)
Stems: The stem of hydrophytes shows the following adaptations.
1. In most of the hydrophytes the stem is long, slender, spongy and flexible; e.g., Hydrilla,
Potamogeton etc.
2. The stem may float horizontally on water surface (e.g., Azolla) or may be thick, short and
stoloniferous; e.g., Eichhornia. It may be attached to the bottom of the pond by a rhizome (e.g.,
Nymphaea).
Petiole The petioles have special modifications to suit the aquatic environment. Following are
some of the modifications.
1. Long, slender and delicate petioles are present in hydrophytes with their leaves floating on
water surface (e.g., Nymphaea).
2. In some plants petiole is swollen to form a bulb like structure to help the plants to float on
water (e.g., Eichhornia).
Leaves: The leaves of hydrophytes show the following characteristics:
1. In submerged hydrophytes the leaves are thin, long and in the shape of a ribbon, (e.g.,
Vallisneria) or finely dissected (e.g., Ceratophyllum).
2. Floating leaves are large, entire and flat (e.g., Nymphaea). These leaves have a coat of wax.
The leaves may also have hairs (e.g., Salvinia).
3. The leaves of emergent and amphibious hydrophytes are heterophyllous, i.e., the leaves
below the water are long, narrow and dissected while those outside the water are entire and
broad. This is also termed as dimorphism of leaves. Heterophylly is shown in plants such as
Ranunculus, Limnophila heterophylla, Sagittaria, Sagitifolia etc.
Anatomy of Hydrophytes Following anatomical characters are common to all
hydrophytes.
1. All hydrophytes show presence of large air chambers. The tissue that forms air chambers is
termed as aerenchyma.
2. Mechanical tissue, i.e., sclerenchyma is either poorly developed or absent.
3. Vascular tissue, particularly xylem is poorly developed.
4. Cuticle is absent.
5. Stomata are absent in submerged hydrophytes.
Roots Epiblema is not cuticularised. Cortex is mostly parenchymatous. Aerenchyma may also
be present. Xylem is poorly developed in comparison to phloem. Amphibious hydrophytes
show xerophytic characters in addition to hydrophytic characters. The roots of these plants have
well developed mechanical and vascular tissues, besides aerenchyma.
Stem Cuticle is absent in epidermis. Cortex is large and parenchymatous. It is largely made of
aerenchyma. Xylem is poorly developed in comparison to phloem. The vascular tissues are so
reduced that these form a single vascular bundle.
Leaves The leaf epidermis does not have cuticle. However, in floating leaves wax or hairs
cover the upper epidermis. Stomata are present only in the upper epidermis. Stomata are absent
in the in the submerged leaves. Large air chambers and spongy parenchyma are present in the
leaves. Palisade parenchyma is generally absent.
