Rachis
/ˈreɪkɪs/
Definition
Rachis is the main axis of a compound structure in plants, especially the central stem-like part of a compound leaf or an inflorescence, the flower cluster stalk. Leaflets or smaller branches attach along it, which distinguishes it from a simple leaf stalk, or petiole. In ferns, the term also refers to the continuation of the frond stalk above the base, where the leaf blade divisions are attached.
Function in Plants
- Support in compound leaves: In many compound leaves, rachis holds the leaflets in place and helps space them so each leaflet can capture light and shed water efficiently.
- Axis of many flower clusters: In inflorescences, the main flower-bearing axis can be a rachis, and its length and branching pattern influence how flowers and later fruits are displayed.
- Useful for plant identification: Botanists often compare features of the rachis, such as whether it is winged, hairy, grooved, or flexible, when separating similar species or describing varieties.
- Clue to damage and stress: Bending, splitting, spotting, or collapse along the rachis may point to mechanical injury, pests, disease, or water stress, especially in ferns, palms, and plants with compound leaves.
Related Terms
Pinna
Pinna refers to one primary division of a compound leaf or frond, especially in ferns and some palms. It is a distinct…
Pinnae
Pinnae are the primary leaflets or divisions arranged along each side of a central axis in a compound leaf or frond…
Leaflet
Leaflet refers to one of the individual blade-like sections of a compound leaf, where a single leaf is divided into…
Midrib
Midrib refers to the main central vein of a leaf blade. It runs from the leaf stalk, or petiole, toward the tip and is…
Spike
Spike refers to a type of inflorescence, or flower cluster, in which individual flowers are attached directly to the…