Introduction

The Euphorbia species most familiar to readers of the Monthly Weed Post is likely leafy spurge (E. esula), but 1,600 to 2,000 Euphorbia species exist worldwide, mainly in tropical regions, but also in temperate regions including 15 to 17 (depending on the source) in Montana. Species in Montana include annuals and perennials; native and non-native; and small, ground-hugging species (e.g., corrugate-seed broomspurge (E. glyptosperma)) to tall, erect species (e.g., leafy spurge). At this time of year, at least in floral departments, a particularly bold and beautiful Euphorbia appears in northern climates like Montana, E. pulcherrima, commonly called “poinsettia.” Latex-like sap is a key characteristic of “Euphorbs” along with fascinating inflorescences that often are showy due to large and colorful bracts, which are leafy-like structures surrounding the base of the flower. Three species are described in more detail below.

Native

A close-up of a plant with yellowish-green flowers. Green grass is in the background.

Warty spurge. Photo: Matt Lavin, Flickr.

A native species with a particularly descriptive common name is warty spurge (E. spathulata). In Montana warty spurge is primarily found east of the Continental Divide, and it tends to inhabit sparsely vegetated areas at lower elevations. This plant has a few distinctive characteristics to help set it apart from leafy spurge. First, it is an annual and will have a small taproot compared to leafy spurge’s extensive root system. Like leafy spurge it has oppositely arranged leaves and white, sticky sap, but the leaves are oblong, meaning they are more rounded in shape. Finally, once plants are mature enough to have a seed capsule, you will see warty appendages that give this plant its common name.

Non-native and Invasive

A green plant with yellow flowers.

Leafy spurge. Photo: Jane Mangold, MSU.

Leafy spurge is a widespread noxious weed in Montana and is problematic for displacing native plant communities, reducing crop yields and cattle forage production, and toxicity to livestock and humans.  It is a long lived, perennial forb that grows 8 to 36 inches tall and, true to a Euphorb, has showy bracts. The bracts are yellowish-green and surround small clusters of yellow flowers. Leaves are narrow and lance-shaped. Leafy spurge is adapted to many habitat types from dry hillsides to riparian areas and often infests rangelands, pastures, roadsides and disturbed areas in Montana. Leafy spurge is difficult to control for a variety of reasons including a deep and perennial root system, seed capsules which explode dispersing seeds up to 15 feet away, and seeds which can remain viable in the seed bank for up to 15 years.

Ornamental

A close-up of red flowers with small, yellow centers. Dark green leaves surround the red flowers.

Poinsettia. Photo: Iowa State University Extension

Poinsettia is native to southern Mexico where it can grow to be a large, woody shrub reaching 10 feet tall. Many decades of breeding led to the ornamental varieties available today in white to pink to red colors, which are due to the bracts changing in color in response to shorter winter days. Actual flowers are small, green to yellow, and clustered at the center of the showy bracts. The sticky, white sap can cause a skin rash and contact with it should be avoided while this bold and beautiful species decorates the house.  

Further Information

For more information about this month's weed post, contact Extension Invasive Plant Specialist Jane Mangold. Past posts are available in the Monthly Weed Post Directory.

THis weed post is also available as a printable PDF (248 KB).