Air plants are often mistakenly assumed to be succulents due to their shared reputation for being drought-tolerant and easy to care for. Air plants, belonging to the genus Tillandsia, are not succulents; they represent a completely different biological classification and survival strategy. Succulents store water internally in specialized tissues, while air plants absorb moisture and nutrients externally from the atmosphere. These fundamental differences in anatomy and physiology mean they have distinct care needs despite their similar hardiness.
What Makes a Plant a Succulent
A plant is classified as a succulent based on a structural adaptation called succulence, which involves developing thick, fleshy parts to retain water. This water storage capacity is concentrated in specialized parenchyma cells located within the leaves, stems, or roots. Species like Echeveria and Aloe are primary examples of leaf succulents, where the majority of the stored water is held within the plump foliage.
The primary function of the root system in succulents is twofold: anchoring the plant firmly in the soil and acting as the main pathway for water and nutrient uptake. Because they live in arid environments, many succulents have evolved a shallow but widespread root network to maximize the collection of scarce rainfall. To minimize water loss, many also possess a waxy, protective layer called a cuticle on their surface, which acts as a barrier against evaporation.
Many succulents also employ Crassulacean Acid Metabolism (CAM photosynthesis) to conserve moisture. This process allows the plant’s stomata, the tiny pores used for gas exchange, to remain closed during hot daylight hours. They only open their stomata at night to take in carbon dioxide, drastically reducing water lost through transpiration. This sophisticated internal water management system is a defining characteristic of succulents.
The True Identity of Air Plants
Air plants (Tillandsia) are classified as epiphytes, meaning they naturally grow upon objects like trees, rocks, or utility wires without drawing nourishment from their host. This lifestyle dictates that they cannot rely on a traditional root system for survival, which is the main divergence from succulents. Their roots are primarily used for mechanical support, serving only to anchor the plant to a surface.
The survival mechanism for Tillandsia is external, relying on specialized structures called trichomes that cover the leaves. These microscopic, scale-like appendages give many air plants a silvery, fuzzy, or gray appearance, especially those adapted to drier habitats. When moisture lands on the leaves, the trichomes quickly absorb the water and nutrients directly into the plant.
Trichomes also serve an important protective function, shielding the plant from intense sunlight and reducing the rate of water evaporation after absorption. The more silvery and dense the trichomes are, the more adapted the variety is to sunny, arid conditions. This unique absorption method means the entire surface of the air plant’s leaves functions as the equivalent of a succulent’s root system and storage tissue combined.
Why Their Care Needs Are So Different
The distinct anatomical features of air plants and succulents translate directly into different requirements for successful cultivation. Succulents require a loose, well-draining soil environment to support their anchoring roots and prevent waterlogging. Watering a succulent must be deep and infrequent, allowing the soil to dry out completely between sessions so the plant can draw upon its stored reserves.
Air plants, conversely, will quickly suffer and develop rot if they are placed into soil or kept constantly wet because their roots are not built for constant moisture. Their care demands water be absorbed through the trichomes on the leaves, achieved through regular misting or periodic full-plant soaks. These soaking periods, which can range from twenty minutes to a few hours, simulate the tropical rain or heavy dew from which they naturally draw water.
Air circulation is a greater concern for Tillandsia than for succulents due to the way they absorb moisture. After soaking, an air plant must be allowed to dry fully within a few hours to prevent the growth of fungus or rot at the base. Succulents, with their thick cuticles and internal storage, can tolerate higher levels of direct sun exposure, though this varies by species. Air plants, particularly greener varieties with fewer protective trichomes, prefer bright, indirect light, as intense, direct sun can easily scorch their surfaces.