The genus Sedum, commonly known as stonecrop, is a succulent. This large group of plants, comprising between 400 and 500 species, has evolved specific features to survive in dry conditions. Stonecrops are known for their hardiness and ability to thrive where other plants struggle. They are native primarily to the Northern Hemisphere, extending into mountainous regions and the tropics.
Defining Succulent Characteristics
A succulent is classified by physiological and morphological traits that allow for water storage. The primary feature is specialized water storage tissues, often resulting in thick, fleshy leaves or stems. These tissues enable the plant to swell and shrink as water is taken up or used.
Succulents also minimize water loss, a process known as transpiration. They possess a thick cuticle, a waxy layer on the surface of the leaves and stems that prevents evaporation. Many succulents, including Sedum, utilize Crassulacean Acid Metabolism (CAM), a modified form of photosynthesis. This adaptation means the plant opens its stomata, the tiny pores for gas exchange, only at night when temperatures are cooler, significantly reducing water loss during the day.
The Sedum Genus and Classification
The Sedum genus belongs to the plant family Crassulaceae, which is known as the stonecrop family. This family is dominantly succulent, clearly establishing Sedum’s identity. The classification confirms that the genus shares the fundamental, water-retaining strategy common to all succulents.
Sedum species are categorized as leaf succulents because they primarily store water in their thick, fleshy leaves. These leaves have a high cellular elasticity and a low surface-area-to-volume ratio, which is highly efficient for water storage. This internal water reservoir allows the plant to be temporarily independent of external water supply.
The leaves of stonecrops are coated with a protective, thickened cuticle and often display a waxy coating, known as farina, which further limits water loss. Many Sedum species employ the CAM photosynthetic pathway. By opening the pores only at night to take in carbon dioxide, the plant conserves its stored moisture, allowing it to endure periods of drought.
Diversity of Sedum Forms
The Sedum genus is diverse, encompassing a wide range of growth habits, which can sometimes confuse those new to the plant. The genus includes species that are low-growing, mat-forming groundcovers, as well as taller, upright varieties. Despite these visual differences, the underlying physiological trait of succulence remains consistent across the entire genus.
Creeping Sedum varieties, such as Sedum acre or ‘Angelina’, are typically low to the ground and spread horizontally, making them excellent ground cover. Upright varieties, like the popular ‘Autumn Joy’ or Sedum spectabile, grow taller and form clumps, often reaching heights of one to two feet. Both forms rely on their fleshy, moisture-taining leaves to survive in dry conditions. This means that regardless of whether a Sedum is a tiny trailer or a robust clump, it has the inherent drought-avoidance strategy of a succulent.