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Euphorbia esula, commonly known as the Green Spurge or Leafy Spurge, is a species of spurge native to central and southern Europe (north to England, the Netherlands, and Germany), and eastward through most of Asia north of the Himalaya to Korea and eastern Siberia.[1][2][3]
Detail of flowers and immature seeds
It is a herbaceous perennial plant growing to 1-1.2 m tall, with several stems branched from the base. The stems are smooth, hairless or slightly hairy. The leaves are small, lanceolate, 4-8.5 cm long and up to 1 cm broad, with a slightly wavy margin. The flowers are small, produced in umbels with a basal pair of bright yellow-green petal-like bracts. Clusters of the bracts appear in late spring, while the actual flowers do not develop until early summer. All parts of the plant contain a toxic white milky sap.[3][4]
It reproduces readily by seeds that have a high germination rate and may remain viable in the soil for at least seven years. The seed capsules open explosively, dispersing seed up to 5 m from the parent plant, and may be carried further by water and wildlife. Leafy Spurge also spreads vegetatively from the root system, which is complex, reported to reach 8 m into the ground and 5 m across, and may have numerous buds.[5]
There are two subspecies and a hybrid subspecies:[1][3]
- Euphorbia esula subsp. esula. Leaves broadest near apex; umbel bracts 5-15 mm. Throughout the range of the species.
- Euphorbia esula subsp. tommasiniana (Bertol.) Kuzmanov (syn. E. waldsteinii (Sojak) A.R.Smith; E. virgata Waldst. & Kit.). Leaves broadest at the middle; umbel bracts 12-35 mm. Eastern Europe, western Asia.
- Euphorbia esula nothosubsp. pseudovirgata (Schur) Govaerts. Hybrid between the above two subspecies.
As an invasive plant
Leafy Spurge was transported to the United States possibly as a seed impurity in the early 1800s. First recorded from Massachusetts in 1827, Leafy Spurge spread quickly and reached North Dakota within about 80 years. It now occurs across much of the northern U.S., with the most extensive infestations reported for Montana, North Dakota, Nebraska, South Dakota, and Wyoming. It has been identified as a serious weed on a number of national parks and on reserves of The Nature Conservancy in eleven northern states. It is now classified as an invasive species by the United States Department of Agriculture.[6][5] It is also naturalised in Canada and parts of South America.[1]
It displaces native vegetation in prairie habitats and fields through shading and by usurping available water and nutrients and through plant toxins that prevent the growth of other plants underneath it. It is an aggressive invader and, once present, can completely overtake large areas of open land.[5]
Because of its persistent nature and ability to regenerate from small pieces of root, Leafy Spurge is extremely difficult to eradicate. Biological control offers a highly promising management tactic for Leafy Spurge. Goats, apparently able to graze on the plant without ill effect, have been used on rail trails in Idaho to clear leafy spurge from the trail shoulders.[7] The U.S. Department of Agriculture has shown success using six European insects that feed on Leafy Spurge. These include a stem and root-boring beetle (Oberea erythrocephala), four root-mining flea beetles (Aphthona spp.) and a shoot-tip gall midge (Spurgia esulae). Large scale field-rearing and release programs are carried out cooperatively by federal and state officials in many northern states. The results are not as immediate as when herbicides are used but, if pesticide use is kept to a minimum, large numbers of these insects build up within a few years and have shown impressive results.[5]
Several systemic herbicides have been found to be effective if applied in June, when the flowers and seeds are developing, or in early to mid-September, when the plants are moving nutrients downward into the roots. Preliminary research suggests that chemical treatment in the fall followed by a spring burn to reduce seed germination may be an effective strategy for reducing Leafy Spurge infestations. Multiple treatments are necessary every year for several years, making leafy spurge control an extremely expensive undertaking. If left uncontrolled for a single year, Leafy Spurge can reinfest rapidly. Prescribed burning, in conjunction with herbicides, may also be effective.[5]
As a model weed
Leafy spurge is being developed as a model to answer fundamental questions of weed biology. Over 55,000 ESTs have been sequenced from all plant tissues including tissues from plants that were cold-stressed, drought stressed, and plant being attacked by both flea beatles and gall midges. Analysis of the EST sequences indicated that 23,000 unique sequences representing more than 19,000 unigenes were obtained. These sequences are now available on Genbank. The unigenes have been used to develop cDNA microarrays that also include more than 4,000 additional cDNAs from cassava (another Euphorb related to leafy spurge). These microarrays are being used to identify physiological processes and signals that regulate bud dormancy (one of the main reasons leafy spurge is difficult to control), and invasiveness.
References
- ^ a b c Germplasm Resources Information Network: Euphorbia esula
- ^ Flora Europaea: Euphorbia esula
- ^ a b c Blamey, M. & Grey-Wilson, C. (1989). Flora of Britain and Northern Europe. ISBN 0-340-40170-2
- ^ Huxley, A, ed. (1992). New RHS Dictionary of Gardening. ISBN 0-333-47494-5
- ^ a b c d e U.S. National Park Service description
- ^ InvasiveSpecies.gov
- ^ "War on Weeds," Rails to Trails Magazine, Spring 2004, p. 3
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