Posted by: Kara Harders CSUE and NRCS
[Dictionary definition for prostrate: BOTANY- growing along the ground.]
Common Purslane, Spotted Spurge, Prostrate knotweed and Puncturevine . Can you tell them apart? These four have much in common, but where they differ is very important.
All four are annual weedy forbs (non-grasses). They enjoy many of the same conditions, such as hanging out in lawns, gardens, and sides of roads/paths. You may wonder “If they are so similar does it matter if I can tell them apart?” Read on to learn why!
Prostrate spurge - C. maculata L.
Prostrate spurge is the only toxic plant of the four, its stems produce a milky latex juice when broken, and it is the only plant of the four which is native to North America. This plant has a slight variant within the species, Spotted Spurge, which looks the same but with a small purple spot on each leaf. Leaves are ovate, slightly hairy, and generally dark green. The flowers are tiny and pinkish, which will go unnoticed to an untrained eye. Seedpods are 1/16 inch or less long and the oblong seeds are about 1/25-inch-long. Be sure to wear gloves when hand weeding this plant! See picture below, and notice the milky sap!
Prostrate knotweed - Polygonum aviculare L.
Also a non-native annual, growing 1 to 3 feet tall, with wiry corrugated stems. The leaves of this weed are hairless, alternate, and lance-shaped to oval, 1/2 to 2 1/2 inches long and 1/8 to 1/3 inch wide. Flowers are small and pink, occurring in clusters along the flower stems at leaf axils. Flowering stems compose about half of the height of a mature plant. It was likely introduced to North America with the first colonists and was first collected in Canada in 1821.
See picture below.
Common purslane - Portulaca oleracea
A non-native, fleshy weed with succulent like leaves, this prostrate annual was introduced in the Americas as early as the 16th century and has made its way around the world. A possible reason for its wide distribution is its historic role as a medicinal plant and edible plant, meaning it was likely, at times, spread intentionally. High in a variety of nutrients, this plant in grown intentionally in some places, but its ability to easily reproduce and visual similarity to the toxic Prostrate Spurge has made it undesirable in many lawns, gardens, and fields. Small yellow flowers will produce many small black to brown seeds within a brown seed pod.
*Please note that this article does not contain enough information to teach or instruct people to consume weeds or other herbs for culinary purposes, please do additional research if that is something you are interested in.
See picture below.
Puncturevine - Tribulus terrestris
Another non-native annual, Puncturevine is mat forming, with trailing stems, each can be 1/2 to 5 feet long. With small, hairy, oval leaves, it can look similar to the prostrate spurge. A key identifying figure are its flowers, which are yellow, 1/3 to 1/2 inch wide with 5 petals, And of course, its seed pods. These seed pods develop as a larger pod of 5 sections that break at maturity into tack-like structures with sharp, sometimes curving spines. These seeds will remain dormant in the soil for 4 to 5 years, so even when they appear controlled one year, they may come back the next. This is one of the later flowering weeds, with blooms not coming on until July to October. See picture below.
These four plants do not make up all of the prostrate weeds we have here in Colorado but they should help you distinguish between the most common problematic ones.
When you are trying to identify a weed and are unsure of what you have, try to identify what time of year it grows, the flower size, structure, and color, and other factors so you are better able to research it, or present your problem weed to another person to try to get an ID.
Remember, you can’t properly control a weed until you know what kind it is!