By Mary Ann King
It’s all in the way they are grouped. The gardener only needs to remember the three classifiers of genus, species and cultivar for identification purposes. A genus encompasses a group of species that are closely related.
Species is a more specific classification within the genus group and can produce fertile offspring. For example in the name Sedum glaucophyllum, Sedum is the genus and glaucophyllum the species of Appalachian stonecrop that grows well in rocky alkaline soil.
A cultivar further classifies the sedum that has been selected for desirable traits. With Sedum glaucophullum ‘Dazzleberry’ on the plant tag, the plant may appear burgundy instead of green.
Knowing these classifications will help in understanding the difference between sedum, succulents, and cactus. The word succulent is used to describe the plant characteristic and is not a formal classification. Succulents have some parts of the leaves, roots or stems that are thickened and fleshy, and retain water in arid climates or soil conditions. Within the same genus there may also be plants with succulent attributes and a normal plant stem. Lots of plants have some succulent characteristics that allow them to adapt to dry conditions. Succulents originated in arid regions and have features that allow them to survive drought.
Cactus retains water within the plant structure, which is also a succulent characteristic. Cacti commonly have thorns. Hobby cactus growers often separate cacti from succulents by presence or absence of thorns rather than strictly by the botanical classification that are sometimes harder to see. Cacti are members of Cactaceae family. Because plants may have adaptations to dry conditions that make them appear related, this adds to confusion.
Sedum is a genus of flowering plants that also have the succulent characteristics of water storing leaves and stems. Sedums are part of the Crassulaceae family. Sedum is also commonly called stonecrop because of its stone like appearance. Appalachian stonecrop has a white flower. With 600 species found in the Northern Hemisphere, sedums vary from annuals, perennials, and creeping herbs to shrubs. Sedum and cactus have succulent characteristics but come from two different families within the plant hierarchy.
If a gardener wishes to develop a rock garden or to grow drought resistant plants, seeking cultivars with succulent characteristics would be a good choice. These plants are beautiful and have unique body forms. There are numerous varieties of cultivars that are low growing or tall, flowering and creeping plants that, once established, require minimal care.