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.

Growing from a taproot, crown vetch puts forth branching stems which 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 generally stands upright at heights of one to two feet (0.3 to 0.6 metres), although stems reaching six feet (1.8 meters) in length also occur. Underground, its rhizomes, which sprout roots and shoots, may attain lengths of 10 feet (3.04 meters).

Because they are in the legume family, they produce seeds in pods, which are one to two inches (2.5 to 5 centimeters) in length. Seed pods, which are segmented, are borne as crown-like clusters. Seeds, which are numerous, have a cylindrical shape with a brownish color.

Crown vetch leaflets are lanceolate, meaning that, having the shape of a lance, their length exceeds their width. Their coloring is dark green.

Leaflets alternate and are odd-pinnate (imparipinnate), i.e., two rows of leaflets with a terminal leaflet. Leaflets may total anywhere from fifteen to twenty-five on a stem.

Crown vetch produces small half-inch (1.27 centimeters) flowers, colored pink and white or lavender-purple and white. Clustered on a stalk at the tips, flowers bloom from early in the spring to late in the autumn.

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).

Because of its rapid growth and spread, by both rhizomes 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.

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.

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.

Control methods include

• herbicides for large infestations
• burning
• manual removal, and
• mechanical removal by mowing.

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.

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Pohick Creek, Fairfax County, northern Virginia: dw_ross, CC BY 2.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:20100603e2.jpg; MostlyDross, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/dw_ross/4669114245/

near Přerova, northeastern Czech Republic: Rigel7, Public Domain (CC0 1.0), via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:PP_Na_Popovickem_kopci_019_cf_Securigera_varia.jpg

Steve Hurst, ARS Systematic Botany and Mycology Laboratory: Steve Hurst/ARS, Public Domain, via USDA-NRCS PLANTS Database @ https://plants.usda.gov/home/plantProfile?symbol=SEVA4

Gallagator Trail, Bozeman, Gallatin County, northwestern Montana: Matt Lavin, CC BY-SA 2.0, via Flickr @ https://www.flickr.com/photos/plant_diversity/5181772127/; Matt Lavin, CC BY SA 2.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Coronilla_varia_(5181772127).jpg

New Observatory Woods State Natural Area, Dane County, south central Wisconsin: Joshua Mayer (wackybadger), CC BY-SA 2.0, via Flickr @ https://www.flickr.com/photos/wackybadger/4315475240/

Millennium Park, Kent County, west central Michigan: Rachel Kramer (rkramer62), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/rkramer62/7182326125/

Bodenheim, western Germany: Vera Buhl (VBuhl), CC BY-SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:2010-06-26_(23)_flower.JPG

SEVA4: USDA Natural Resources Conservation Service, Public Domain, via USDA PLANTS Database @ https://plants.usda.gov/home/plantProfile?symbol=SEVA4&mapType;=distribution

purple crown-vetch Securigera varia (L.) Lassen: following curve of highway guard rail: James H. Miller, USDA Forest Service, Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5379526

Millennium Park, Kent County, west central Michigan: Rachel Kramer (rkramer62), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/rkramer62/7188586311/

Lisbon, west central Portugal: Joaquim Alves Gaspar (Alvesgaspar), CC BY-SA 3.0, via Wikimedia Commons @ https://en.wikipedia.org/wiki/File:Cichorium_intybus-alvesgaspar1.jpg

umbel head of crown vetch's inflorescence: Audrey (audreyjm529), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/audreyjm529/169216074/

Crown vetch's fernlike leaflets alternate on each leafstalk in an odd-pinnate arrangement, with one leaflet at the top: Patrick J. Alexander, Public Domain, via USDA PLANTS Database @ https://plants.usda.gov/home/plantProfile?symbol=SEVA4&mapType;=distribution

closeup of crown vetch's umbel-shaped inflorescence: Schnobby, CC BY-SA 3.0, via Wikimedia Commons @ https://fr.wikipedia.org/wiki/Fichier:Coronilla_varia.jpg

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.

USDA NRCS Plant Materials Program. "Crownvetch Coronilla varia L." USDA Plants Database > Plant Fact Sheet. February 1, 2002. United States Department of Agriculture Natural Resources Conservation Service. Web. plants.usda.gov

• Available at: http://plants.usda.gov/factsheet/pdf/fs_cova2.pdf