I have always called this plant “spurge”. An annual native, spurge is found in open and disturbed areas throughout all of the United States and much of Canada. A prolific seed producer, spurge becomes a problem along walkways and roadways and in lawns, gardens, orchards and amid vegetable crops. Because it is difficult to control, spurge is considered a noxious weed.
For such a common plant, I never gave it much thought and believed doing a post on spurge would be simple. Wrong!! The taxonomy of “spurge” is very confused. There are several spurge species that are similar in general appearance and habitat. I finally decided that this specimen was prostrate spurge (Euphorbia maculata), only to encounter more confusion. Some taxonomists classify Euphorbia maculata in the genus Chamaesyce. So the literature refers to the same plant as either Euphorbia maculata or Chamaesyce maculata. And there is more. Spotted spurge differs from prostrate spurge in having a dark spot in the center of each leaf. However spotted and prostrate spurge are often classified together as E. maculata. Figuring out what plant I was actually dealing with was not simple. I am still not certain of the absolute correctness of my identification.
Prostrate spurge grows flat or partially erect when in competition with other plants, often forming mats. Rising from a taproot, the stems turn pale red in the sunlight. When the stems are broken, the acrid, milky latex exuded can be irritating to the skin and cause rash. The latex is also poisonous and carcinogenic. The opposite pairs of leaves are dark green, oblong in shape and smooth or slightly toothed.
Prostrate spurge has a type of “false flower” or pseudanthium – an inflorescence or group of flowers that collectively resemble a single flower. Five fused bracts form a cup-like structure inside of which are stamens (the male flower) surrounding a stalk holding the ovary (female flower). Four nectar glands with petal-like extensions along the upper edge are near the edge of the cup. As it matures the ovary stalk bends back and becomes a three-chambered fruit. Each chamber contains one seed. This whole inflorescence is called a cyanthium. A prostrate spurge cyanthium has neither petals nor sepals.
The nectar glads of prostrate spurge attract bees, flies and wasps. Many gamebirds eat the seeds, particularly morning doves.
Prostrate spurge is also called milk purslane and milk spurge among other common names.
These prostrate spurge samples were growing in our gravel driveway (Modoc County CA).