Snow-on-the-Mountain
Euphorbia marginata
Spurge family (Euphorbiaceae)

Description: This adventive or introduced annual plant is 1-3' tall, branching frequently and often having a bushy appearance. The round stems are initially dull green, but become light brown with age. Young stems have abundant white hairs, while older stems become more glabrous with age. The alternate leaves are up to 3½" long and 1" across. They are ovate or obovate, glabrous, smooth along the margins, and sessile or nearly so. The upper surface of the leaves often has a white margin of varying width; this white margin has a tendency to become broader and more conspicuous as the leaves approach the flowers. The leaves (or leafy bracts) immediately below the flowers are smaller in size and often opposite or whorled, otherwise they are similar to the other leaves. As a plant matures, there is a tendency for the lower leaves to turn yellow and fall off the stems, particularly during dry weather.

The upper stems terminate in small clusters of flowers. The structure of these flowers is typical of members in the Spurge family, although their size is larger than average. Both the male and female flowers develop within a cyathium, which is about ¼" long and shaped like a cup. This cyathium is covered with white hairs on the outside and has 5 glandular appendages along its rim at the top. Each petal-like appendage is white and more broad than long. The male flowers are without sepals or petals, consisting of stamens with anthers that are not exerted significantly from the cyathium. Each female flower is without sepals or petals, consisting of a 3-valved pistil with 3 divided styles. The pistil of the female flower is about 1/3" across and is strongly exerted from the cyathium from a short stalk that is either nodding or erect. Like the cyathium, the pistil is covered with white hairs, and its valves are well-rounded. The blooming period occurs from mid-summer to early fall and lasts about 2-3 months. There is no noticeable floral scent. Both the cyathia and male flowers wither away, while each female flower becomes a 3-celled seed capsule. Each of these cells contains a single seed. The seeds are oval in shape, and their surface is reticulate and rather bumpy (tuberculate). They can be flung several feet from the mother plant by mechanical ejection. The root system consists of a stout taproot. This plant spreads by reseeding itself.

Cultivation: The preference is full sun and mesic to dry conditions. This plant also adapts to slightly moist soil (if flooding doesn't occur) and isn't particular about the type of soil. It has few problems with pests and disease, and is quite drought resistant.

Range & Habitat: Snow-on-the-Mountain naturalizes occasionally in scattered counties across Illinois, particularly in the NE and west-central regions of the state. This plant is adventive from an area that lies west of Illinois, where it is native to the Great Plains. It also escapes from cultivation occasionally. Habitats include dry upland areas of prairies, hill prairies, areas along railroads and roadsides, pastures and fallow fields, dumps and landfills, and waste areas. The seeds often survive earth-moving operations and can germinate wherever the soil is dumped. Snow-on-the-Mountain is often grown in gardens because of its attractive foliage. In the Great Plains states, this species is regarded as a pest because it has a tendency to spread in pastures. In Illinois, Snow-on-the-Mountain appears to be less aggressive and persistent, more often occurring in waste ground and other highly disturbed areas.

Faunal Associations: The flowers attract small to medium-sized bees, including Augochlorella striata (Green Metallic Bee sp.), Nomia nortoni (Norton's Alkali Bee), and Melissodes comptoides (Miner Bee sp.). It is also possible that various flies and wasps are attracted to flowers. The seeds are eaten by Mourning Doves. The foliage contains a toxic and irritating white latex that deters mammalian herbivores. More information is available about the floral-faunal relationships for this species, but it is applicable to the Great Plains and Western states, rather than the Midwest.

Photographic Location: A garden at Meadowbrook Park in Urbana, Illinois. The above photograph was taken during the early autumn when the leaves were starting to fall off the stems. The hairy cyathia with their white appendages and the developing seed capsules can be observed in this close-up.

Comments: Snow-on-the-Mountain has a distinctive appearance because of the white-margined foliage. It can't be confused with any other plant species.

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