The plant commonly known as periwinkle is a familiar sight in gardens across the world, instantly recognizable by its vibrant, often blue or purple, blooms. This single common name applies to two distinct types of flowering plants that share a similar appearance and belong to the same plant family. While both are widely cultivated, one is a trailing groundcover prized for its evergreen foliage, and the other is an upright, bushy plant used as a vibrant seasonal annual.
Clarifying the Botanical Identity
The primary confusion surrounding the name periwinkle stems from two separate plant genera within the Apocynaceae, or dogbane, family. The first group is the genus Vinca, which includes the Lesser Periwinkle (Vinca minor) and the Greater Periwinkle (Vinca major). These species originate from Europe and western Asia and are woody, perennial groundcovers known for their long, trailing stems.
The second group is the genus Catharanthus, represented most famously by Catharanthus roseus, commonly called Madagascar Periwinkle or Annual Vinca. This plant is native to Madagascar and grows as a herbaceous subshrub with an upright, bushy habit. The historical confusion is compounded because Catharanthus roseus was originally classified as Vinca rosea in the 18th century before later taxonomic revisions separated it into its own genus.
The Distinctive Botanical Look
The defining characteristic that unites both Vinca and Catharanthus roseus is their flower structure, which is the main reason for their shared common name. Both produce a flower with five fused petals that form a flattened, pinwheel shape. The flowers of Vinca species are typically blue, violet, or white, appearing singly on short, erect stems that rise just above the foliage. Vinca minor flowers measure about one inch across, while Vinca major produces blooms up to two inches wide.
The leaves of the Vinca species are dark green, glossy, and arranged oppositely along the stem. Vinca minor leaves are smaller and more leathery than those of Vinca major. In contrast, Catharanthus roseus is an erect subshrub, reaching heights of 10 to 24 inches, with a dense, bushy appearance. Its flowers exhibit a wider color range, including pink, rose, red, and white, often featuring a contrasting “eye” or throat of a darker color. The leaves of Catharanthus are oblong to elliptic and glossy, but they are generally deciduous in cooler climates, whereas Vinca leaves are evergreen.
Growth Habits and Environmental Impact
Vinca species, the perennial groundcovers, are characterized by aggressive, trailing stems (stolons) that root easily wherever they touch the soil. This rooting ability allows them to spread rapidly and form dense, weed-suppressing mats. They are highly valued for erosion control on slopes and for covering difficult, shady areas, thriving in the understory of trees where many other plants struggle to grow.
This aggressive spreading is why Vinca major and, in some regions, Vinca minor are classified as invasive species. They can escape cultivation and aggressively colonize natural areas, forming monocultures that smother native wildflowers and tree seedlings, thereby reducing local biodiversity. Conversely, Catharanthus roseus, the Madagascar Periwinkle, grows as an upright annual bedding plant in most temperate climates because it is not cold-hardy. It thrives in full sun and high heat, making it a popular choice for summer containers and garden borders.
Chemical Significance and Cautions
Beyond their ornamental appeal, certain periwinkle plants possess a significant chemical profile that has influenced modern medicine. Both Vinca and Catharanthus genera contain indole alkaloids, nitrogen-containing compounds synthesized by the plant. The most scientifically notable of these are the vinca alkaloids, such as vincristine and vinblastine, which are isolated from the leaves of Catharanthus roseus.
These compounds function as anti-mitotic agents, meaning they interfere with the cell division process, making them highly effective in chemotherapy. Vincristine and vinblastine are used in the treatment of various cancers, including leukemia and lymphoma. Other alkaloids are found in Vinca minor, such as vincamine, which has been studied for its potential vasodilatory properties. All parts of both Vinca and Catharanthus roseus are considered poisonous if ingested, and any use of these plant compounds for medicinal purposes must be performed under strict pharmaceutical control.