This so-called ‘weed’ is colorful, gets by on very little water and seems determined to survive

Lowcountry gardeners love purslanes because of their colorful flowers and affinity for hot, dry conditions. Nurseries often carry several versions, sometimes marketed as portulaca or moss rose.

But other purslanes also grow wild in the Southeast. These include common purslane (Portulaca oleracea), which is actually a “parent” of some of the cultivated varieties. Native to western Asia, the species may have been introduced into the United States as a food plant by early European colonists.

Common purslane is a low, sprawling plant with small, yellow flowers. Less showy than its cultivated relatives, it’s often regarded as a troublesome weed.

Ecologists, though, use the term “weed” in a different sense—to refer to a diverse group of plants adapted for survival in disturbed or otherwise inhospitable sites where other species can’t grow.

Common purslane, for example, thrives everywhere from rich garden soil to parched, trampled ground and even sidewalk cracks.

Rigorous weeding isn’t necessarily a deterrent for this tenacious plant. Bits of broken stem can still develop roots and keep growing. And any purslane seeds left in the ground may stay viable for several decades.

One feature helping common purslane colonize dry habitats is a long taproot that probes deeply into the ground for water. Succulent stems and leaves store moisture, too.

Also, when water is scarce, the plant keeps its stomates (leaf pores) shut during the daytime, reducing water loss in the hot sun. At night, when dehydration is less of a problem, the stomates open up, collecting carbon dioxide gas – one of the basic ingredients needed for photosynthesis.

Overnight, purslane stores the gas by converting it into an organic compound called malic acid. During the daytime, malic acid is broken down to release the captured carbon dioxide, which is then made available for photosynthesis.

Common purslane is one of some 16,000 drought-resistant plants, including cacti and many succulents, that show this sort of adaptation, called CAM photosynthesis.

Aside from its interest to biologists, common purslane has been valued for centuries as a raw and cooked vegetable. Traditionally the stems, leaves, and flower buds have been part of a variety of dishes in Europe, Mexico, Asia, and the Middle East. The plant is said to have a sour, salty flavor.

This story was originally published August 7, 2017 at 8:19 AM with the headline "This so-called ‘weed’ is colorful, gets by on very little water and seems determined to survive."