What characterizes a pinnate leaf?

A pinnate leaf is characterized by having leaflets that are attached directly to a central stalk, which is known as the rachis. This arrangement resembles the structure of a feather, where multiple smaller leaflets branch off from a central axis. This configuration allows for more surface area for photosynthesis while maintaining structural efficiency.

In contrast, leaves with leaflets that are attached to the end of the stalk do not exhibit the pinnate arrangement, as they might represent other forms such as palmate leaves, where leaflets originate from a single point at the end of the petiole. A single leaf at each node is indicative of simple leaves rather than compound leaves, which include pinnate types. Finally, leaflets that form a circle around the stem describe a whorled pattern, which is distinct from the linear arrangement characteristic of pinnate leaves. Understanding these differences helps in identifying various leaf structures in plant biology.