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Plants of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

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Common Name
Leafy Spurge (Wolf's Milk)

 

Scientific Name
Euphorbia esula L.

 

Plant Family
Spurge (Euphorbiaceae)

Garden Location
Upland - subject to control

 

Prime Season
Late Spring - Summer

 

 

Leafy Spurge is an invasive perennial plant that is considered a Noxious Weed with prohibited seed distribution. It has smooth stems that are 2 to 3-1/2 feet high, erect and branching near the top.

Leaves are alternate on the stem, linear, with pointed to obtuse tips. On the upper stem below the inflorescence they become more lance-like (wider at the base) and there is usually a small whorl of leaves beneath each flower cluster accompanied by a pair of opposite leaves below the whorl. Within the inflorescence there are a few leaves that are more lanceolate in shape (linear by widest at the middle). The stems, flowers and leaves will emit a white milky toxic sap if broken.

The inflorescence is a terminal umbel, up to 5 inches wide. Stemmed flowers also grow from the leaf axils below. The umbel contains 5 to 17 branches.

The flowers are very small, yellowish-green and are borne above a showy yellow-green bract that forms early in the season on each branch of the umbel. The bract has a special name - a cyathium. Plants of the Euphorbia genus are somewhat unique in this regard. A cyathium is a cup-like structure and inside at its base are nectar glands (greenish-yellow in this species) and these have outward flaring appendages that look like petals. From this base around the nectar glands appear the male flowers, 11 to 20 in this species, which have one stamen each. Rising from the center of the cyathium is the stalk of the single female flower, which has a green 3-lobed ovary with a three-branched style emerging.

Seed: Mature female flowers eventually produce 3 oval seeds, 3 to 5mm long. Seeds disperse up to 15 feet, explosively from a seed capsule, have a high germination rate and will survive up to 7 years in the soil. While it is non-native, it is commonly found throughout Minnesota after introduction from Europe.

It is invasive and toxic. (see below).

 

Habitat: Leafy Spurge grows from a stout caudex which has a deep vertical root and reproduces from seeds and primarily from the underground crown and root buds, which are numerous. Tilling the soil and breaking up the root results in greater growth of the population as a single root bud will create a new plant. It is a common plant of roadsides, dry fields and hillsides and is most aggressive in dry areas. It is allelopathic, that is, it has chemicals that inhibit other forbs from growing near it. Like many invasive plants, it is an early spring starter.

Names: The genus name, Euphorbia, is said to refer to Euphorbus, the Greek physician of King Juba II on Numidia. Euphorbus found medicinal uses of certain plants of this genus. Carl Linnaeus (the author name on the plant classification) named the genus after him. The species, esula, is said to be derived from a Celtic word that meant 'sharp' referring to the acrid juice of the plant. The Euphorbias are a large world-wide genus. There are 14 members of the genus with known populations in Minnesota and several others were once reported but there are no collected specimens.

Comparisons: Another Euphorbia that is native to Minnesota, not invasive, and grown as an ornamental for its many late summer white flowers is Flowering Spurge, Euphorbia corollata L. Another Euphorbia found at Eloise Butler is the Wild Poinsettia, Euphorbia cyathophora.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

plant Leafy Spurge

Above: 1st photo - Note the yellowish-green bracts which show off the small flowers. 2nd photo - Leafy Spurge growing invasively within a community of other plants.

Below: 1st photo - Flower buds developing. 2nd photo - Each branch of the umbel bears a cyathium - a cup-like structure. As shown here these can have a first level with a second series rising from the first - in this case two additional cyathium are rising on stalks from the first, which has in its center a set of male flower parts. The upper sections are developing their own reproductive parts.

buds Flower

Below: 1st photo - In the center of the lower cyathium are yellow-green nectar glands, each with a pair of outward flaring appendages. Beneath these are the male flowers which each put up a single stamen; and flopped over on its side is the female ovary with the three-branched style. 2nd photo - The fertilized ovary has swollen in size showing the characteristics 3 chambers. Below are the remains of the nectar glands and above is the decaying style. To the upper right is a second cyathium with its own ovary and styles, but development looks aborted.

cyathium green seed capsule

Below: When the seed capsule is mature it splits open explosively and dispels the seed. Each ovary can produce 3 seeds. At left are the pieces of a seed capsule, a green immature seed and an almost mature brown mottled seed.

Seeds

Below: 1st photo - The narrow linear leaves of the stem below the inflorescence. 2nd photo - The characteristic whorl of leaves just below the branching of the inflorescence with a pair of opposite leaves below the whorl.

Leafy Spurge leaves Leafy Spurge upper whorl

Below: When uncontrolled, Leafy Spurge will form large masses, blocking sunlight from other plants and secreting a chemical that prevents other plants form growing.

patch of leafy spurge

Notes:

Noxious Plant Notes: The plant is generally classified as a noxious weed and in Minnesota as invasive, thus it is regulated by being on the list of Prohibited Noxious Weeds. 22 states have the plant on some type of control list. The seed capsule can emit seeds explosively up to 15 feet from the plant. The seed remain viable for up to seven years. Like most noxious weeds it is tolerant of a wide range of habitats with the main threat being to prairies and savannas where it can quickly displace native species. In 1982, then Garden Curator Ken Avery recruited volunteers to help control it in the Garden. Prescribed burning with an application of glyphosate and 2,4-D works, but not in a native plant area. The Minnesota DNR states that the most effective eradication method for a small patch is with Picloram, but only as a last resort as the chemical persists in the environment. Certain root boring beetles are known to provide biological control as explained below. It is believed the plant arrived in the U.S. in the early 19th century as a seed impurity. It was first recorded in Massachusetts in 1827.

Toxic: The milky latex juice of the plant has toxic effects on humans and animals. Foraging on the plant has been known to be deadly to animals. They can't digest it and it produces a stomach ache. Goats and sheep, however, eat it. There is some concern that the toxin is carcinogenic to humans. Kinghorn, in his book, Toxic Plants (Ref. #15), devotes an entire chapter to the carcinogenic and irritant properties of the Euphorbiaceae and details some of the chemicals found in this species.

Control experiment: In the western grasslands Leafy Spurge has infested almost 800,000 hectares in Montana, the Dakotas and Wyoming. Grazing domestic sheep helps control the plant if the sheep have access to it early in the plant's life cycle. The plants then produce fewer flowers and seeds. An study by Eva Masin, University of Montana, determined that grazing sheep preferred non-native forbs such as Leafy Spurge when they were in abundance compared to native forbs. In her study area, sheep grazed 89% of the non-native forbs vs 28% of the native forbs. This of course, may be due to the higher non-native population to begin with, but it does show that infestations on rangeland can be mitigated by grazing. (Info from Kelseya, Winter 2011, Montana Native Plant Society)

Other control methods involve using the Flea Beetle and the Leafy Spurge Stem-boring Beetle, which lays eggs in the roots and the hatching larva eat the roots. Simply taking the time to cut down the stalks before seed production will greatly reduce numbers over time. (Info from Kelseya, Fall 2014, Montana Native Plant Society)

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.

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