Euphorbia hypericifolia | Pest Rating Proposals and Final Ratings

California Pest Rating for

Graceful spurge | Euphorbia hypericifolia L.

Malpighiales: Euphorbiaceae

Pest Rating: A | Proposed Seed rating: N/A

PEST RATING PROFILE

Initiating Event:

This plant given a Q rating as a potential invasive weed on 11/2/2017 (PDR 19TPO6465546).

History & Status:

Graceful spurge (Euphorbia hypericifolia, synonym Chamaesyce hypericifolia) is an upright perennial herb with arching, openly branched flowering stems to 60 cm tall, but often low when mowed. The leaves are opposite, ovate, with small teeth. The flowers are small, even by spurge standards (0.5 – 1 mm) and are borne in dense heads in the axils of the upper leaves. Seeds are expelled forcefully from capsules up to 4 meters away. Cattle avoid foraging on spurge when possible, but goats and sheep are generally immune to its irritant properties and may develop a preference for it. It grows in disturbed areas, in evergreen woodland and in crop fields. It is also found in nurseries as a weed. The common horticultural container plant Euphorbia ‘Diamond Frost’ is sometimes attributed to Euphorbia hypericifolia. Nevertheless, it is not closely related to this species, nor is it weedy. Therefore, this attribution is in error and should not be used for regulatory action, regardless of labelling.

Official Control: Graceful spurge was just recently detected in recently imported nursery stock, and, although weedy, it is native to the southeastern U.S. So, there is no official control.

California Distribution: It is not yet fully established in California, although it has been detected in weedy situations several times.

California Interceptions: Vouchered specimens are known from San Diego County as weeds.

United States: It is native to the Southeastern U.S.

International: Graceful spurge is native to the New World as a tropical to subtropical weed. It is introduced in warmer areas of the Old World.

This risk Carnation spurge would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: The plant has adapted to warm, well-watered areas throughout the world, so it could spread widely as a nursery weed, but is not otherwise likely to spread except to irrigated situations. Graceful spurge receives a Low (1) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Host Range: Risk is High (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Graceful spurge produces via numerous seeds that are able to spread via nursery stock and other means. The seed bank is moderately persistent. Graceful spurge receives a Medium (2) in this category.

Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Graceful spurge can lower nursery productivity, and require more intensive weed control activities in nurseries. If is escapes into horse paddocks and other irrigated pastures, it could poison livestock. Graceful spurge receives a High (3) in this category.

Evaluate the economic impact of the pest to California using the criteria below. Score:

Economic Impact: A, B, D, F

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Graceful spurge is not likely to spread widely beyond disturbed, human-mediated landscapes, as California is too dry to favor its growth. Graceful spurge receives a Low (1) in this category.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 1

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Graceful spurge: Medium (10)

Add up the total score and include it here.

–Low = 5-8 points

–Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Graceful spurge has been found in in several counties in California, but does not seem to be well established. It receives a Low (-1) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

–Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score

The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (10)

Uncertainty:

Graceful spurge has not yet widely established in California due to the paucity of appropriate habitat. Nevertheless, it has shown its ability to spread and thrive in similar climates to those it is found in in Florida as a nursery or garden weed. It could almost certainly do the same in California.

Conclusion and Rating Justification:

Graceful spurge is a significant nursery weed. It deserves an A rating as the nursery industry in California would be harmed by the establishment of this weed; its rarity in California raises the possibility of excluding it by timely regulation.

References:

Brunel S, G. Schrader, G. Brundu & G. Fried. 2010. Emerging invasive alien plants for the Mediterranean Basin. Bull OEPP/EPPO Bull. 40:219–238.

Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/).

Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford.

Gregor T. & L. Meierott. 2013. Report 72. Euphorbia hypericifolia L. – P. 277. In: Vladimirov V., Dane F., Stevanovič V., & Tan K, eds. New floristic records in the Balkans: 22. Phytol Balcan.19: 267-303.

S. Sciandrello, S., G. Giusso del Galdo & P. Minissale. 2016. Euphorbia hypericifoliaL. (Euphorbiaceae), a new Alien Species for Italy. Webbia 71: 163-168.

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6650; plant.health[@]cdfa.ca.gov.

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