Rachis

Rachis

With the term rachis, in botany, we mean the central axis, in continuity with the petiole, of compound leaves, on which the leaflets are inserted, or the main axis of an inflorescence.
The rachis is therefore the axial cauline organ, from which short ramifications originate according to a bilateral symmetry.

The rachis is present, for example: in the inflorescence of the Poaceae, and is the main axis of the ear; in compound leaves, the extension of the petiole on which the leaflets are inserted or, in place of these, other secondary rachidae.
The secondary rachis is called rachilla, like that of the spikelets of the Poacee, each of which is in turn inserted on a main spine.