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Weed Alert!

Hypericum canariense L.
(Canary Island St. Johnswort)

Summary: new plant of unknown characters
Hypericum canariense has recently been observed invading natural areas in San Mateo, Santa Barbara and San Diego counties in California. It is thought to have escaped from cultivation, as it has traits desirable to horticulturists (i.e. attractive, ornamental foliage and large, bright orange flowers). Native to the Canary Islands, it has been found growing in the wild in disturbed places, coastal sage scrub, and in grassland habitats up to 100 meters in elevation in coastal areas of California. H. canariense has the potential to extend its range inland from its present coastal distribution.

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Small plants

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Big infestation
Photos compliments of John Wade; JWSavsLand(at)aol.com

Hypericum canariense is a shrub in the Hypericaceae (formerly Clusiaceae) - St. Johnswort family. H. canariense can grow up to 5 meters tall and has simple, opposite leaves that are oblong-lanceolate, with tapered bases. They range in size from 2 to 7 cm long. The yellow-orange flowers are large and showy with petals (12 to 15 mm in size) and stamens that persist after flowering. The sepals are ovate with pointed tips and have ciliate hairs along their margins. The fruits are leathery capsules that open at maturity (Hickman 1993). Although the plant has features desirable to horticulturists and is thought to have escaped from cultivation (CDFA 2001), it is currently not widely grown as a garden or landscape plant. A web search in November 2001 revealed that it is kept at the Los Angeles Arboretum and that seeds are offered for sale on the internet (Platt 2001), but on the whole the plant does not seem to be widely offered at wholesale or specialty nurseries in North America.

Scientific and Common Names:
The genus name Hypericum is derived from the Greek hyper, meaning over, and eikon, meaning an icon or apparition (over an apparition). It was thought to have been able to protect one from evil spirits and has been used in several Greek names such as Hyperion or Hyperides. The species epithet canariense means "of the Canary Islands." The common name of St. Johnswort is from its association of St. John the Baptist. There are currently no accepted synonyms for H. canariense.

The overall impacts of this new invader are unknown, but H. canariense appears to outcompete and exclude nearly all other vegetation once it has invaded. In coastal California areas that have become infested, H. canariense can comprise up to 90 to 100% of the vegetation cover, and it outcompetes and excludes both the native scrub vegetation (Baccharis spp., Toxicodendron diversilobum) as well as other non-native vegetation such as jubatagrass (Cortaderia jubata). The only native plants that persist after H. canariense invasions are trees that are over 1.5 m tall (J. Wade, personal communication). In favorable conditions, infestations of H. canariense can spread at a rate of up to 45-90 meters per year.

Native Range:
H. canariense is native to the Canary Islands, where it is often located in xerophytic scrub or forested zones, from 150 to 800 meters in elevation. It can be very common locally (Bramwell & Bramwell 1974).

Range As An Invader:
In North America, H. canariense occurs as an invader in Hawaii and in California (USDA-NRCS 2001). Previous reports from California list this species as being present only in San Diego and Santa Barbara counties in southern California (CalFlora 2001). The Jepson Manual: Higher Plants of California (Hickman 1993) lists the species as uncommon in disturbed places below 100 m in the South Coast subregion of the state. In San Diego, H. canariense has escaped cultivation as an ornamental near the Point Loma military cemetery (M. Kelly, pers. comm.).

In San Mateo County in northern California, H. canariense currently covers approximately 25 to 40 hectares (62-99 acres) near Gazo Creek (J. Wade, pers. comm.). John Wade of the Pescadero Conservation Alliance reports that there are several populations of H. canariense along the coast, and that they are all rapidly expanding in range.

Furthermore, an infestation of at least 2-3 acres was reported in January 2003, on Angel Island, Marin County (P. Warner, pers. comm.).

Reproduction and Methods of Dispersal:
H. canariense produces large amounts of viable seed. Many seedlings have been found just downslope of mature shrubs in San Diego County (M. Kelly, pers. comm.).

Little information is available on successful control methods for H. canariense. It could be difficult to manually remove with a weed wrench unless the ground is very soft because of its large root system. Such mechanical approaches may not be successful unless the entire root and stem portions are completely removed, as it may resprout (J. Wade, pers. comm.).

Mike Kelly (personal communication) has been successful controlling H. canariense by using the cut-stump herbicide application method. He first cut the stems with a chainsaw, then applied the herbicide glyphosate (brand name RoundUp) at full strength to the cut-stump. Mike suspects that a less-concentrated solution of herbicide might also be effective, but has not tested the efficacy of differing amounts of herbicide on H. canariense control.

1. Bramwell, D. and Z. Bramwell. 1974. Wildflowers of the Canary Islands. Stanley Thornes, Ltd., London.
2. CDFA. 2001. California Department of Food and Agriculture-Weed Management (http://pi.cdfa.ca.gov/weedinfo/HYPERICU2.html)
3. Hickman, J.C. (ed.). 1993. The Jepson Manual: Higher Plants of California. University of California Press, Berkeley.
4. Kelly, M. 2001. California Exotic Pest Plant Council. Personal communication.
5. Platt, K. 2001. The Seed Search (http://www.seedsearch.demon.co.uk/), site accessed November 2001.
6. USDA, NRCS. 2001. The PLANTS Database, Version 3.1 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
7. Wade, J. 2001. Pescadero Conservation Alliance. Personal communication.
8. Warner, P. 2003. California Dept. of Parks & Recreation. Personal communication.

--Mandy Tu/Wildland Invasive Species Team (original author, November 2001)
--Barry Rice/Wildland Invasive Species Team (updates: January 2003)

Updated January 2005
©The Nature Conservancy, 2001