**5. Variability and classification**

There is great variability in the secreted materials of glandular trichomes: polysaccharides, sugars, salts, lipids, essential oils, resins, proteins, etc. Uphof [6] proposed to classify glandular trichomes according to the nature of their secretory products. Fahn [7] classified secretory substances in plants in general into two groups:


The difficulty with this type of classification is that some glands secrete more than one type of substance. For example, the glands of *Inula viscosa* secrete lipophilic substances, polysaccharides, and proteins at different stages of life and by different organelles [8]. In some carnivorous plants, the same glandular hairs produce both seductive (nectar) and digestive substances (enzymes).

In Lamiaceae, in addition to lipophilic substances, relatively large amounts of polysaccharides, which vary in amount between species, are secreted by certain capitate glands [8]. Many of these secreted materials are phytotoxic.
