Chapter 5 Solutions — Morphology of Flowering Plants

In a compound leaf, the incisions of the lamina reach all the way to the midrib, breaking it into a number of separate leaflets. Compound leaves are of two types based on how the leaflets are arranged.

Pinnately compound leaf:

- Leaflets (pinnae) are arranged on both sides of a common central axis called the rachis.

- The rachis represents the midrib of the original leaf.

- Example: Neem (Azadirachta indica).

Palmately compound leaf:

- Leaflets are all attached at a single common point at the tip of the petiole (like fingers from a palm).

- There is no rachis; all leaflets radiate from one point.

- Example: Silk cotton (Bombax ceiba).

Key difference: In pinnate leaves, leaflets are arranged along a rachis (feather-like); in palmate leaves, all leaflets arise from a single point (hand-like).

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. There are three main types:

1. Alternate phyllotaxy:

- A single leaf arises at each node alternately.

- Successive leaves are arranged in a spiral pattern up the stem.

- Examples: China rose (Hibiscus rosa-sinensis), mustard (Brassica), sunflower (Helianthus).

2. Opposite phyllotaxy:

- A pair of leaves arises at each node, lying opposite to each other.

- The two leaves in a pair are on directly opposite sides of the stem.

- Examples: Calotropis procera, guava (Psidium guajava).

3. Whorled phyllotaxy:

- More than two leaves arise at each node and form a whorl (ring) around the stem.

- Example: Alstonia scholaris (devil's tree).