petiole, the stalk of a plant’s leaf which supports the leaf blade or lamina. Petioles are stem tissue and branch from the main stem of the shoot having similar anatomical features. At both ends of the petiole are swellings that alter the position of the leaf blade according to such stimuli as water stress and low light. Samples of petioles taken at flowering are used as a basis for assessing a vine’s status in terms of vine nutrition
The characteristics of petioles vary with vine variety and growing conditions, being longer on vigorous vines. Between varieties, petiole length varies from 5 to 20 cm (2–8 in), petiole colour varies from green to red, and petioles may vary from smooth to hairy. These features help in the identification of varieties (see ampelography).