Crown Vetch Nightmare

The common names of Securigera varia (L.) Lassen are crown vetch or purple crown vetch.

A synonym for Securigera varia is Coronilla varia. The synonym’s genus name, a diminutive form of the Latin word corona (“crown”), recognizes the annular (“ringlike”) arrangement of the flowers on their stalk. The common name links crown, for the coronal floral arrangement, with vetch, a corruption of the Latin word vicia (“bean plants”), recognizing that Securigera varia is in the legume family, Fabaceae.

Native to northern Africa, southwest Asia, and Mediterranean Europe, Securigera varia was introduced into the United States and Canada in the 1950s as ground cover in erosion control.

What crown vetch looks like

Crown vetch reaches a height of one to two feet. Small half-inch flowers, colored pink and white or lavender-purple and white, cluster on a stalk at the tips from early in the spring to late in the autumn.

Growing from a taproot, its branching stems rise vertically and also trail horizontally. As it vines along the ground, it creates a canopy of dark green esthetically interspersed with its pastel flowers. Crown vetch stands upright at heights of one to two feet (0.3 to 0.6 metres).

Because they are in the legume family, they produce seeds (numerous, brown, cylindrical) in pods, which are one to two inches (2.5 to 5 centimetres) in length.

Its leaflets are lanceolate, meaning that, having the shape of a lance, their length exceeds their width, and that they end in a pointed tip.

Leaflets alternate and are odd-pinnate (imparipinnate), i.e., two rows of leaflets with a terminal leaflet.

Horses: Clover slobber is preferred to Crown vetch paralysis

Whereas the Rhizoctonia leguminicola fungus, an extrinsic plant pathogen, is the culprit in equine slobberings after grazing on clover, nitroglycosides that are intrinsic to Securigera varia may retard growth in horses, paralyze their hind quarters, or even cause their death. Nitroglycosides are plant toxins, of which coronarian is toxic to horses and other single-stomached (nonruminant) animals. Coronarian inhibits succinate dehydrogenase, an enzyme that is critical for equine energy metabolism. Fatal toxicity occurs with the development of methemoglobinemia, wherein the horse’s blood is unable to carry oxygen to its tissues, producing abnormal levels of methemoglobin (oxygen-carrying protein hemoglobin with its iron in the ferric state) in the blood and tissue hypoxia (oxygen deprivation).

Proliferation

Because of its rapid growth and spread, by both rhizomes (underground stems that sprout roots and shoots) and seeds, crown vetch effectively counters soil erosion in damaged soils. Crown vetch is not disturbed by eroded soil. As a member of the legume family Fabaceae, crown vetch establishes a symbiotic (Greek: sýn "with" and bíōsis “living”) relationship with rhizobia as its host plant. Rhizobia are soil bacteria that are classed as diazotrophs because they effectuate the essential process of nitrogen fixation. The process entails converting nitrogen gas, which they have extracted from the air, into a form of nitrogen that the host plant is able to use. As a result of this symbiotic relationship, crown vetch rehabilitates the soil content to acceptable levels for its survival.

The negative extreme of its easy proliferation is that Securigera varia quickly establishes control of areas, thereby banishing other desirable species. Its planting for purposes of erosion control along roadsides and rights-of-way and in open fields has provided crown vetch with a strong base of operations from which to spread. The hardy plant flourishes in poor soil, where there is little competition, and keeps extending its territory. Its seeds retain their viability in soil for several years, which increases not only their timeline for propagation but also their opportunities.

Crown vetch invasion

Soon Securigera varia borders and then tackles gardens and lawns, weakening and oftentimes eliminating cultivated plants. As such, crown vetch is now considered to be an invasive species: their domination of their environment disrupts the habitat balance by adversely affecting the floral profile.

With this impairment in biodiversity, the ecosystem suffers imbalances and even abandonment. So a new kind of erosion --- the erosion from the plethora of polyculture to the paucity of monoculture --- is established.

Distribution in Canada and the United States

Crown vetch, which is not native to the United States of Canada, has become naturalized extensively throughout these two North American countries.

In Canada, Securigera varia is found in all of the provinces. Although crown vetch has been reported on Newfoundland, it is not yet documented in Labrador. Crown vetch is not found in any of the three territories, so far.

In the United States, crown vetch has been documented in all states except Alaska and North Dakota. Securigera varia has been sighted in the nation’s capital, Washington, D.C. but it has not been reported in Puerto Rico nor has it been recorded in the U.S. Virgin Islands.

How to control Securigera varia

Control methods include

*** herbicides for large infestations

*** burning

*** manual removal, and

*** mechanical removal by mowing.

Spring’s Securigera varia in my lawn

Purple crown vetch has made an impromptu appearance along the entire south side of my house. Specimens have also clustered around the west side of my house, to the south of the back stoop.

Moreover, purple crown vetch now arcs around the southwest curve of the ornamental rocks that bolster my house number at the opening into the eastern expanse of my yard. Situated a few feet from the road and from the entrance to my driveway, Securigera varia is readily visible to all passersby.

That welcome glimpse previously was proferred by chickory (Cichorium intybus), for which we fondly named my house Chickory Cottage. Chickory’s peaceful blue flowers blazed from a diminished number of plants last summer. Apparently crown vetch was already casting covetous rhizomes and seeds in the direction of the gentle chickories, which have beneficial uses, in addition to their loveliness, that have been enjoyed in the United States since their naturalization here in the 1700s.

The nightmare invasion by Securigera varia has been progressing with great determination, unbeknownst to me.

But now I know, and there is no way that my house is being renamed Vetch Cottage.

“Crown vetch.” Plant Fact Sheet. U.S.D.A. Natural Resources Conservation Service-Plant Materials Program. February 1, 2002. http://plants.usda.gov/factsheet/pdf/fs_cova2.pdf

“Crown Vetch Coronilla varia.” Invasive Plant Species Fact Sheet. Invasive Plant Species Assessment Working Group. Indiana Department of Natural Resources-Division of Forestry. October 2006. http://www.in.gov/dnr/files/Crown_vetch.pdf

Knight, Anthony P., and Richard G. Walter, eds. A Guide to Plant Poisoning of Animals in North America.  Jackson WY: Teton NewMedia, 2001.

Panda, H. Handbook on Medicinal Herbs with Uses. Delhi, India:  Asia Pacific Business Press, 2004.

My special thanks to talented photographers who make their fine work available on the internet:

***  Dan Tenaglia, Missouriplants.com, Bugwood.org,  for “Flower: Crown Vetch” and for “Foliage Securigera varia (L.) Lassen”

***  Bogdan of Bucureşti, România for “Securigera varia”

***  Joaquim Alves Gaspar (Alvesgaspar)of Lisboa, Portugal for "Blue wild flower of Cichorium intybus"

Copyright April 19, 2011 by Derdriu