The term “periwinkle” refers to two completely different organisms: a flowering plant and a marine snail. Despite sharing a common name, these organisms belong to separate biological kingdoms and possess unique characteristics. The plant is a popular horticultural groundcover, while the animal is a common mollusk inhabiting coastal areas. This article clarifies the differences between these unrelated species.
The Botanical Periwinkle
The plant known as periwinkle belongs to the genus Vinca and is a member of the dogbane family, Apocynaceae. The two main species used in landscaping are Vinca minor (lesser periwinkle) and Vinca major (greater periwinkle). This perennial is valued for its trailing, subshrub habit, which quickly forms a dense, evergreen ground cover. The stems root at the nodes as they creep along the soil, allowing the plant to spread rapidly by vegetative propagation.
The glossy, dark green leaves provide year-round color in gardens. Vinca minor leaves are typically smaller than those of Vinca major. In the spring, the plant produces distinctive, five-petaled, phlox-like flowers that are commonly violet-purple or lavender-blue, though white cultivars also exist.
Often called “creeping myrtle” in the United States, periwinkle is widely used as a low-maintenance, shade-tolerant ground cover. It is a popular choice for planting under trees or on slopes where turfgrass struggles to grow. Its dense growth habit is effective at suppressing weeds and is valued in ornamental gardening.
The Marine Periwinkle
The marine periwinkle is a type of sea snail classified as a gastropod mollusk within the genus Littorina. The common periwinkle, Littorina littorea, is frequently encountered in the intertidal zone of rocky coasts and tide pools. These small snails possess a spiral, rounded shell that varies in color from brown to gray, often reaching about one inch in length.
A defining physical trait is the operculum, a hard, trapdoor-like structure that seals the shell opening when the snail retracts. This structure allows the periwinkle to resist desiccation and survive long periods out of the water during low tide.
As a grazer, the periwinkle uses a ribbon-like structure called a radula, covered in tiny teeth, to scrape algae and detritus from rock surfaces. Periwinkles are resilient, tolerating wide fluctuations in temperature and salinity necessary for life in the harsh intertidal environment. They move by gliding on a muscular foot coated in mucus, which helps them adhere firmly to rocks, resisting the force of crashing waves.
Ecological Roles and Human Interaction
The two periwinkles have distinct functions in their respective ecosystems and different relationships with humans. The botanical periwinkle is frequently planted for its ability to stabilize soil on slopes and banks, making it a functional choice for erosion control. However, the same vigorous growth contributes to its potential as an invasive species in non-native regions, such as North America.
In forest understories, the Vinca plant can spread rapidly, forming dense, low-growing mats that suppress and displace native wildflowers and ground cover. This vegetative spread allows it to dominate the forest floor, reducing local plant diversity. The leaves are also unpalatable to most grazing wildlife, further contributing to its unchecked growth.
The marine periwinkle plays a crucial role in coastal food webs as a primary consumer. By constantly grazing on microalgae, the snails help prevent any single species of seaweed from dominating the rocky shore. The common periwinkle (L. littorea) is non-native to North America, introduced from Europe, and its intense grazing may have altered intertidal habitats by competing with native species. Beyond its ecological function, the sea snail is considered a traditional culinary delicacy in many coastal cultures, especially in Europe, where it is hand-harvested for human consumption.