Flowers of Securigera varia
Securigera varia, also known as Coronilla varia, is a tough, aggressively-spreading, low-growing legume (to 60cm (~2 ft.)). Known for its beautiful crown-like inflorescence, its other names include crown vetch and purple crown vetch. The native range of crown vetch is Eurasia and northern Africa, but it has become established in Australia, Canada, New Zealand, and the USA (including British Columbia).
Due to its complex system of creeping rhizomes, crown vetch is often used for erosion control on embankments, roadside plantings, and shorelines. It can also tolerate urban environments, requiring little to no fertilization or mowing. Its deep taproots and sprawling vegetative mass also contribute to it being an excellent competitor. Although it has a long germination period of six months, once plants have established in an area, they can become invasive. Plants can spread rapidly by both seed and rhizome. While the thick foliage prevents other plant species from establishing, it also provides shelter to meadow voles, ground-nesting birds and rabbits.
Small clusters of 1cm (~0.5 inch) bi-coloured leguminous flowers bloom in early summer to late autumn. It is typical for them to have white lower petals and pink upper petals, as in today’s photograph. These mildly fragrant blossoms are clover-like, borne in an inflorescence of 10-25 flowers at the end of a leaf-free stem around 15cm (6 in.) in length. The flowers are cross pollinated by long-tongued bees, such as honeybees, who feed on the nectar secreted from the outer surface of the calyx. The foliage consists of pinnately-compound, dark-green alternating leaves, with each leaf having 11-25 leaflets. The fruit of Securigera varia is a grouping of finger-like thin legumes.
Crown vetch is toxic to non-ruminant mammals like humans and horses. The toxins include the cardiac alkaloid, coronillin, which can cause paralysis or even death when consumed. However, ruminants have the capability to degrade the aliphatic nitro compounds; for mammals like cows, sheep, goat, elk, and deer, crown vetch can be grazed or incorporated into hay and provide suitable nutrition. The root nodules of this perennial also fix atmospheric nitrogen to the soil in association with rhizobial bacteria, and can thereby aid in soil rehabilitation.
Many years ago, when I was naive about invasive species, I planted Crown Vetch along a steep eroding clay bank above Lake Huron. It did the job. Some years later, I was amazed to find my garden above the bank full of Indigo Duskywing butterflies. Although the duskywing caterpillars normally feed on wild indigo (Baptisia tinctoria), they managed to switch to the Eurasian invader, vetch.
Oh that the Law of Unintended Consequences was always so benign, if not rewarding 🙂
One of my favorite roadside attractions.
I actually harvested a dried seed pod from the embankment of the Museum of Anthropology, and have been growing a crown vetch in a hanging basket for 2 years. Just today it bloomed for the first time. I had no idea what it was until it now, beyond that it was a vetch, as they had all finished blooming when I got the seeds.