The surface of a plant often has a fine coating of hairs, giving it a fuzzy or frosted appearance. These microscopic structures are known as trichomes, which are outgrowths of the plant’s epidermis, or skin. The term “trichome” originates from the Greek word for “hair,” and these appendages vary in shape, size, and density across different plant species. They can be single-celled filaments or complex, multicellular structures that interact with the environment.
Glandular vs. Non-Glandular Trichomes
Trichomes are classified into two main categories: non-glandular and glandular. Non-glandular trichomes are primarily structural. These can appear as simple, straight hairs, star-shaped (stellate) structures, or sharp, pointed spikes. They form a dense, fuzzy barrier on the surface of leaves and stems, creating a physical impediment for insects and other organisms.
Glandular trichomes, on the other hand, function as microscopic chemical factories. These structures consist of a stalk that elevates a glandular head, which is a cluster of secretory cells. It is within this head that the plant synthesizes and stores a wide array of chemical compounds. The morphology of these glandular trichomes can differ among plant species, reflecting their specialized functions.
The Functions of Trichomes
The purposes of trichomes are diverse. One of their primary roles is physical defense, where the dense matting of non-glandular trichomes can make it difficult for herbivores to consume plant tissue. Sharp or hooked hairs can deter smaller insects, while some glandular trichomes produce sticky substances that physically trap insects.
Trichomes also offer protection from environmental stressors. A thick layer of these hairs can shield the plant from intense sunlight and harmful UV radiation by reflecting light. This same layer helps to reduce water loss by creating a boundary of still air at the leaf’s surface, which traps humidity and slows the rate of transpiration. This adaptation is particularly useful for plants living in windy or arid conditions.
Glandular trichomes are also central to a plant’s chemical interactions. The compounds they produce, including terpenoids and flavonoids, can be toxic or repellent to pests and pathogens. Conversely, the aromatic compounds released from these trichomes can attract pollinators or beneficial predatory insects that help protect the plant.
Trichomes on Common Plants
Many common plants offer clear examples of trichome functions. The tomato plant, for instance, has a noticeable fuzz on its stems and leaves composed of various trichomes. When brushed against, its glandular trichomes rupture and release oils, producing the plant’s characteristic sharp aroma that can deter certain pests.
Stinging nettles provide a dramatic example of a trichome-based defense mechanism. Their trichomes are structured like tiny hypodermic needles that, upon contact, break off and inject a cocktail of irritating chemicals into the skin, causing a painful sting. On the other end of the sensory spectrum is the lamb’s ear plant, known for its soft, woolly leaves. This dense mat of non-glandular trichomes is an adaptation that helps the plant conserve water in sunny and dry climates by reducing evaporation from the leaf surface.
The cannabis plant is perhaps one of the most well-known examples regarding trichome function. Its compounds, including cannabinoids like THC and CBD, as well as the aromatic terpenes, are all synthesized and stored within the capitate-stalked glandular trichomes. These mushroom-shaped structures are concentrated on the plant’s flowers, and their appearance is often used by cultivators to gauge the optimal time for harvest.