trichomen

Trichomen, commonly referred to as trichomes, are specialized epidermal outgrowths found on the surfaces of many land plants. They range from single-celled, hair-like projections to complex multicellular structures and can be non-glandular (for physical protection) or glandular (for secretion). Trichomes occur on leaves, stems, fruits, and, in some species, seeds.

There are several major forms of trichomes. Non-glandular trichomes are often simple or branched hairs that provide a physical barrier against herbivores and reduce water loss by altering the boundary layer of the leaf surface. Glandular trichomes secrete substances such as essential oils, resins, or mucilage, which can deter pests, attract pollinators, or play a role in plant–microbe interactions. Examples include glandular trichomes that produce cannabinoids in cannabis and essential oils in many aromatic herbs.

Functions attributed to trichomes include defense against herbivory, protection from ultraviolet radiation, reduction of transpiration, and temperature regulation of the leaf surface. They can also influence leaf reflectance and appearance, and in some crops, trichome density or type affects pest resistance and market value. Some seed trichomes, such as the long fibers of cotton, are commercially important as textile fibers.

Development and variation: trichomes develop from epidermal cells and their formation is influenced by genetic regulatory networks as well as environmental factors such as light, temperature, and humidity. Species differ markedly in trichome density, size, shape, and chemical secretions, making trichomes useful markers in taxonomy and plant identification.

In summary, trichomen are diverse epidermal structures that contribute to a plant’s protection, interaction with the environment, and, in some species, economic value.