Trichomes, as a plant protective barrier against natural hazards such as herbivores, ultraviolet (UV) irradiation, pathogen attacks and excessive transpiration, play a key role in development of plants and occur widely in various plants. Trichomes may be unicellular or multicellular and are derived from aerial epidermal cells in leaves, stems and floral organs. They are classified as either glandular or non-glandular: the former can contribute to the accumulation and secretion of some alkaloids to resist insects, such as nicotine and terpenoid alkaloids, and the latter can strengthen the role of resistance in abiotic stress by promoting normal plant growth, under condition of extreme high or low temperature, drought and UV irradiation. The origination and spatial and temporal distribution of trichomes are well suited mechanisms for studying cell differentiation, fate choices and morphogenesis. Over time, some previously unknown mechanisms have been elucidated.
Trichomes are a model system for cell differentiation, cell cycle regulation, cell polarity and cell expansion, according to different distributions on leaves, and can be divided into three categories: large, small and glandular trichomes. Large trichomes are commonly observed on the abaxial surface, above the vascular bundles and along the margins, small trichomes in stomatal Para cellular and glandular trichomes, which are regularly distributed wholly or partly in sub epidermal tissue of the leaf surface.