In hydrophytes stem is long. Slender spongy and flexible which often covered with mucilage.CORRECT OPTION IS (B).

Excessive aerenchyma is a characteristic feature of hydrophytes.

Explanation:

Aerenchyma is a specialized tissue in plants that contains air spaces, which help in the exchange of gases between roots and the atmosphere. Hydrophytes are plants that grow in water or in soils that are waterlogged for most of the year. These plants have evolved several adaptations to survive in waterlogged environments, and excessive aerenchyma is one such adaptation.

Excessive aerenchyma in hydrophytes serves the following functions:

1. Improved gas exchange: The air spaces in aerenchyma tissue allow for better diffusion of gases like oxygen and carbon dioxide. This is crucial for the survival of hydrophytes as they grow in waterlogged environments where the supply of oxygen is limited.

2. Reduced weight: Hydrophytes need to be lightweight to float or stay submerged in water. The presence of aerenchyma tissue reduces the weight of the plant, making it easier for it to stay afloat or submerged.

3. Buoyancy: The air spaces in aerenchyma tissue provide buoyancy to the hydrophyte, helping it to stay afloat in water.

4. Storage: Aerenchyma tissue can also serve as a storage tissue for nutrients, allowing hydrophytes to survive in nutrient-poor environments.

In contrast, mesophytes, heliophytes, and xerophytes have less aerenchyma tissue as they do not grow in waterlogged environments and do not require excessive gas exchange or buoyancy adaptations.

Aerenchyma helps hydrophytes to float in water as they increase their buoyancy