Euphorbia cyparissias is an herbaceous to semi-woody perennial that is 15-30 cm (6-12 in.) tall. This plant has an extensive underground root system which allows it to reproduce vegetatively via lateral root buds. When broken, the stems and leaves exude a white latex that characterizes this plant family. The plant has numerous bright green linear leaves that are located alternately along the stem and in whorls where they subtend the inflorescence. The leaves are 1-3 cm (0.4-1 in.) long and 1-3 mm (0.04-0.1 in.) wide. The flowers open in May and can persist through August. The flower structure of E. cyparissias is complex. The flowers are located in a cyme at the top of the plant. The true flowers are small, and lack sepals or petals. They are clustered in a structure called a cyathium which consists of many staminate flowers (male) clustered around one pistilate flower (female). This cyathium is in turn enclosed by an involucre that has four horned glands that are yellow green when young and turn to an orange brown with age. From this involucre come two cordate (heart-shaped) bracts which are a conspicuous bright yellow green turning to purple red as they age. The bracts are 4-6 mm (0.25 in.) wide. The fruit is three lobed and contains 1-3 egg shaped smooth gray seeds that measure 1.5-2 mm (0.08 in.). Page References Bailey 618, Fernald 968, Gleason & Cronquist 338, Holmgren 317, Magee & Ahles 703, Newcomb 408, Peterson & McKenny 162,374. See reference section below for full citations.
Euphorbia esula L. (Leafy spurge). E. esula is another invasive species that looks similar to E. cyparissias. The most obvious difference between these two plants is that E. esula is much taller and more robust than E. cyparissias. E. cyparissias has many more linear shaped leaves that measure 1-3 mm wide (0.04-0.1 in.) as opposed to the fewer and wider (3-8 mm (0.1-0.3 in.)) leaves of E. esula. Finally, E. cyparissias has smaller bracts than E. esula.
Euphorbia cyparissias can reproduce both sexually and vegetatively. Some of the plants in the United States and Canada are in fact sterile, though there are reports of both types of plants in New England. There is some evidence that the plants are self-sterile, thus colonies that are offspring of a single seed are barren, while colonies that are from multiple seeds are reproductive. The fruit of E. cyparissias are explosively dehiscent, and seeds are known to be dispersed by ants. The plant reproduces vegetatively via lateral root buds, forming extensive clonal populations.
Euphorbia cyparissias is found from England to Siberia, though the actual native range of this plant in Eurasia is not known. In the United States, this plant has been reported from all states with the exception of Nevada, New Mexico, Arizona, Texas, Louisiana and Mississippi. It has been reported from all New England states.
It is not known exactly how E. cyparissias was introduced into New England. It was likely introduced from England into North America as an ornamental at sometime in the mid-1800s. It was noted by Gray (1867) to have escaped from gardens and naturalized in Essex County, Massachusetts. It was introduced into Ontario, Canada in 1870.
Euphorbia cyparissias is most often a threat along edges, in yards and other severely disturbed areas. This plant can be present in huge numbers in some of these disturbed areas. The capability of this plant to reproduce vegetatively makes it a greater threat than if it were dependent on seeds for reproduction. Euphorbia cyparissias is considered to be an agricultural pest because it is potentially toxic to horses and cattle. Humans can also be sensitive to the latex contained in the plant.