The oldest public wildflower garden in the United States
Euphorbia corollata L.
Late Summer to Autumn
Flowering Spurge grows up to 3 or 4 feet high; the bright green stem is unbranched below the inflorescence. Juice of the plant is milky and acrid, as in most spurges.
Leaves are alternate on the lower stem and just below the inflorescence is a distinctive whorl. They are oblong, up to 5/8 inches wide and 6x longer than wide, sessile or with very short stalks. There is a prominent mid-vein, the top side is a medium green, the underside paler in color due to very fine surface hair. In autumn the leaves and stem can pick up a very colorful pinkish-red to scarlet color.
The inflorescence is a many-branched loose panicle above a distinctive whorl of leaves. The panicle usually has 5 main branches but six branches are not uncommon. The number of leaves in the whorl beneath the inflorescence also varies, many times there are six, sometimes only 5 and when the main branching is 6 branches there is usually a 7th. Each main branch of the panicle can repeatedly subdivide, usually into fewer branches than the division below it, but sometimes repeating, until only 1 branch remains - i.e. 5 then 4 then 3 then 2 and sometimes one. This is not rigid, 4 seems to be skipped a lot, 3 and 2 seem to be repeated a lot. Branching may stop at any point without getting down to 1. Subtending each of these divisions is a set of small leaves, usually, but not always, equal to the number of divisions, ending with one under a single flower. The flowers are all terminal - at the end of the branch that does not divide any further. See the photo below for an illustration.
Flowers: The small 1/3 inch wide flowers are of a structure unique to the Euphorbia genus. The flower parts are grouped together in a structure called a cyathium. Inside at its base are 4 to 5 nectar glands (greenish-yellow in this species) and these have outward flaring appendages that look like white petals but are instead white bracts. The underside of all this looks like a cup. From this base around the nectar glands appear the male flowers which have one stamen each with a yellow anther. Arising from the center of the cyathium is the stalk of the female flower, which has a green 3-lobed ovary with 3 divided styles emerging. The nectar glands turn reddish as the flower matures.
Seed: Fertile flowers produce 3 oval brown seeds that are released when the dried ovary splits open. Seeds require 30 days of cold stratification for germination. The plant will self-seed.
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. 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.
Habitat: Flowering Spurge grows best in full sun with dry to moderate moisture in loamy soils. It will tolerate partial shade. It grows from a deep woody taproot which makes it hard to eliminate, but it is a beautiful plant.
Names: The genus name, Euphorbia, is said to refer to Euphorbus, the Greek physician of King Juba II of Numidia. Euphorbus found medicinal uses of certain plants of this genus. Carl Linnaeus named the genus after him. The species name, corollata, is Latin meaning 'like a corolla', referring to the appendages of the nectar glands that look like the petals of a normal corolla. The author name for the plant classification - 'L.' is for Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: Another Euphorbia found in Minnesota that has a yellow inflorescence is the non-native invasive Leafy Spurge, Euphorbia virgata. Also look at the Wild Poinsettia, Euphorbia cyathophora.
Above: Flowering Spurge is a sparkle of white in an otherwise non-white late-Summer and Autumn native plant landscape. It blooms August into September. 2nd photo - there are greenish-yellow nectar glands surrounding the center of the cyathium. 3rd photo - note the characteristic whorl of leaves at top of stem just where the inflorescence branches.
Below: The branching of the inflorescence. This plant has 5 main branches above the whorl of leaves. Each branch subdivides, mostly into 3 sub-branches with 3 leaves at the division point. Sometimes the next division is also into 3 and most of those sub-branches have ended in a 2-division branch, with two leaves at the division point. Note that the main branch furthest away in the center of the photo had its first division into only 2 sub-branches. There are no rigid rules here. Small leaves within an inflorescence are frequently called 'bracts'.
Below: 1st photo - The underside of the cup-like cyathium. 2nd photo - Fall color can be a pinkish-red to almost scarlet.
Below: The Euphorbias have a rather different flower system 1st photo - Prior to fertilization the styles with yellow divided tips are visible. 2nd photo -Here you see the fertilized green female ovary rising on its stalk above the male parts of the flower. See above notes for details.
Below: 1st photo - A 3 inch section of the tap root is sufficient to start a new plant that will bloom same year. 2nd photo - Seen here are several intact ovaries that have not yet split open and several that have split along the 3 divisions releasing the brown oval seeds.
Below: A stem leaf: 1st photo - top side, 2nd photo - underside which is paler in color.
Notes: Eloise Butler first recorded planting Flowering Spurge in the Garden on July 27, 1910 and again on Sept. 10, 1910 with plants obtained in Lake City, MN. In 1915 she found it growing in a different part of the Garden. More plants were added in 1922, '24 and '25. Martha Crone planted it in 1948 and 1953. Cary George reported planting it in 1995 and 1998. It is native to Minnesota in counties along the East side of the State from Pine south to the SE corner plus St. Louis County and Renville. General U.S. distribution is the eastern half of the country. 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 of those.
Eloise wrote of this plant: "On dry or sandy soil by the roadsides and on the prairies, throughout the rest of the season, will be found the flowering spurge, Euphorbia corollata. On account of its white, filmy, lace-like inflorescence, it is much used by florists to set off other flowers in bouquets. What seem to be petals in the flower cluster are colored bracts. The flowers themselves are inconspicuous. The Euphorbias form a large family of highly specialized plants, including the small-leaved, pestiferous weedmats [or sandmats], poinsettias and trees in the tropics. One of the characters is a milky sap, which is, in the rubber tree, now indispensable to man." Published July 30, 1911, Minneapolis Sunday Tribune
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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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"