Cannabis sativa L. (cannabis, hemp) plants produce several trichome types on leaf and flower surfaces that include both glandular (secretory) and non-glandular types (leaf hairs). The latter type is produced in great abundance on vegetative tissues, including leaves, stems and petioles of cannabis plants and have garnered little attention compared to the glandular trichomes that manufacture and store a range of cannabinoids. Leaf hairs are found in a majority of plant species and several functions have been attributed to them. These include protection against herbivory, reducing direct sunlight and UV radiation on plant surfaces, reducing transpiration to provide a cooling effect, and in some plant species, accumulating and secreting nutrient salts. Specific studies aimed at elucidating the possible functions of non-glandular trichomes in cannabis plants are lacking due to the overwhelming interest in studying the glandular trichomes that have significant economic importance for producers.

In the present study, symptoms of leaf spots and blighting resembling pathogen infection were observed on the foliage of C. sativa plants grown hydroponically. Symptomatic tissues were subjected to whole genome sequencing and polymerase chain reaction with fungal-specific primers to determine if a microbe was responsible for the symptoms. Neither method revealed a potential fungal or bacterial pathogen. Light and scanning electron microscopic studies of affected tissues revealed the consistent presence of a white powdery crystalline material. X-ray microanalysis confirmed the crystals contained calcium, sodium and several other cations, as well as chloride. The salts were extruded directly from the tips and walls non-glandular trichomes (hairs) present on stems and leaves. Following extrusion through the tips and walls, the salts aggregated around the base of the trichomes, forming white crystalline patches, particularly along leaf veins and on stems. Treatment of plants with excess levels of nutrient salts produced similar symptoms. The ability of non-glandular trichomes of C. sativa to extrude nutrient salts under conditions of excessive fertilizer regimes is described for the first time. The potential roles of these trichomes in transporting salts out of plants exposed to toxic levels of nutrients in the environment and in enhancing salt tolerance warrant further investigation.