Secretory structures of Santolina ligustica Arrigoni (Asteraceae), an Italian endemic species

Abstract

Santolina ligustica Arrigoni (Asteraceae) shows two different types of secretory structures: secretory ducts and glandular hairs. Ducts consist of a lumen varying in width surrounded by one or two layers of secretory cells. The size of the ducts varies in length and width, depending on the organ in which they are present. Hairs are multicellular and biseriate. They consist of two basal, two stalk, and six head cells. Ducts are located in the receptacle, interfloral and involucral bracts, in the stigma, in the leaves, stem, and root. They are absent in the corolla. Glandular hairs are present on the corolla, on the involucral and interfloral bracts, and in the stem and leaves. The histochemical analyses of the secretion of ducts and hairs show the presence of lipids, sesquiterpene lactones, alkaloids, and flavonoids. Although similar, the two secretions differ in the lipid composition: ducts produce both essential oils and resins, while hairs produce essential oils. Pectin-like substances and tannins seem to be produced by glandular hairs only.