Hydrophyte

In the syllabus and the exam

Hydrophyte is examined as the water-habitat counterpart to xerophyte, and candidates are expected to explain how a described or drawn plant's features solve problems specific to living in or on water rather than in dry soil. Typical features include large, thin leaves that float on the surface to maximise light capture, stomata positioned only on the upper leaf surface (since the lower surface sits on water and gas exchange there would be blocked), extensive air-filled aerenchyma tissue running through the stem and leaf, which both keeps the plant buoyant and lets oxygen diffuse down to submerged roots growing in oxygen-poor mud, and a poorly developed or absent cuticle, since water loss is not a problem when the plant is surrounded by water. A frequent mistake is describing a feature that would actually help the plant conserve water, such as a thick cuticle, which contradicts the whole logic of a hydrophyte's adaptation and is penalised. Another common slip is failing to explain why stomata are restricted to the upper surface, simply stating 'stomata are on top' without linking this to gas exchange being blocked on the submerged lower surface. Candidates should also distinguish floating-leaved hydrophytes, such as a water lily, from fully submerged hydrophytes, such as Hydrilla, which instead have thin, finely divided leaves that reduce resistance to water currents and increase surface area for gas exchange directly with the surrounding water.

Example

A water lily has broad, flat floating leaves with stomata only on the upper surface, and air-filled aerenchyma tissue running through its stem, hydrophytic features that keep the leaf afloat and let gas exchange continue above the waterline.

Related terms

AdaptationXerophyteStoma

Source:SRC-DSKP-EN