Question

Which one of the following is a xerophytic plant in which the stem is modified into a flat, green, and succulent structure:
(a)Acacia
(b)Opuntia
(c)Casuarina
(d)Hydrilla

Answer 1

Hint: The plant belongs to the cactus family Cactaceae and is commonly known as Prickly Pear. It is a segmented cactus with spine bearing, blue-green colored, flat, and rounded cladodes.

Complete answer:
Xerophytes (Xero-dry; phyta- related to plants or plants) are the plants that are adapted to survive in dry conditions or regions with less amount of water such as desert or polar regions. Xerophytes such as Opuntia of family Cactaceae have a flat, green, and succulent structure known as Phylloclades (phyllo-leaves; clado-branch) for the function of photosynthesis and resembles branches looking like leaves. Leaves of Opuntia are modified into spines for less transpiration rate and are differentiated into leaves spines and stem spines. The xerophytic plants have several modifications to store water and food for a longer period of time. The succulent structure is the thick & fleshy structure (usually in the form of leaves) for this purpose.
Opuntia is used for the preparation of soup, salads, bread, jellies, etc in many parts of the world whereas in Mexican countries due to its phytochemical properties it is used for medicinal purposes. Its pulp and juices are employed in the wounds and are also helpful in reducing inflammations in the digestive and urinary tracts. Other uses include dye production, biofuel, animal fodder, bioplastic, etc.
So, the correct answer is ‘Opuntia’.

Note: -Acacia and Casuarina are also xerophytic plants and are mostly shrubs or trees with true stems. The former belongs to the plant family Fabaceae while the later to the plant family Casuarinaceae.
-Hydrilla is an aquatic perennial herb and not a xerophyte. It is also known as water thyme. It is a monoecious plant with the true stem growing up to 1 to 2 meters. In comparison to other freshwater aquatic plants, it has been found to have a high resistance to salinity.