Question

Phyllotaxy is decussate in
A. Nerium indicum
B. Pisum sativum
C. Hibiscus rosa-sinensis
D. Catharanthus roseus

Answer 1

Hint: The plant stem bears the leaves which are the sites of photosynthetic activities. Leaves give rise to the foliage of the plant. They are the principal appendages of the plant. The arrangement of leaves on the stem follows a distinct pattern.

Complete answer:
Phyllotaxy can be described as the distribution or arrangement of the leaves present on the stems or branches of the trees. The definite arrangement of the leaves are species specific and ensures the maximum availability of sunlight which is needed for the process of photosynthesis.
Phyllotaxy occurs in three basic types which are alternate, opposite or whorled phyllotaxy arrangement. In alternate phyllotaxy, the leaves arise from different points but they are opposite to each other. The arrangement of leaves in which all the leaves are arranged at the base of the shoot with small internodes. In opposite phyllotaxy, the leaves arise from the same point on the stem and the leaves appear at right angles to each other.
When the arrangement of the leaves appears at the exact right angle to each other on the stem is known as decussate phyllotaxy. This is a type of opposite arrangement of leaves. The leaves appear to be at opposite angles when they are viewed from the top. The leaves arise from a single point.
The decussate phyllotaxy is seen in Catharanthus roseus. It is commonly known as periwinkle. The plant is a subshrub with oval and oblong leaves. The leaves are arranged in opposite pairs and the phyllotaxy is decussated.
Nerium indicum is an evergreen flowering shrub and the phyllotaxy is whorled in which the leaves arise from the single node but are more than two leaves and form a whorl like structure.
Pisum sativum is the pea plant and phyllotaxy is alternate as one leaf is present per node along the stem.
In Hibiscus rosa-sinensis, the leaves are simple and are arranged in the alternate phyllotaxy arrangement.

Hence, the correct answer is option (D).

Note: The leaves on a stem of the plant are arranged in a distinct pattern. This system of arrangement of the leaves in a plant is known as phyllotaxy. In Catharanthus roseus or periwinkle, two leaves arise from the same point on the leaves. This type of arrangement is called decussate phyllotaxy.