Cyclospermum leptophyllum aka Marsh Parsley

Cyclospermum leptophyllum is an annual herb: it lives for one year. It belongs to the carrot family, Apiaceae. People call it marsh parsley, slender celery, or fir leaf celery. Kew and NC State trace its home from Mexico to tropical South America. Useful Tropical Plants says it may first have come from Brazil. It now grows wild through much of the tropics. It also grows in warm temperate zones on several continents. Its sites include fields, thickets, ditches, and ground that people disturb.

Plants form loose mounds with branched stems. The stems stand upright or spread out. NC State gives height and width as 0.5–2 feet [0.15–0.61 metres]. Useful Tropical Plants gives a height near 1.6 feet [0.5 metres]. A taproot holds the plant in place. Green stems have no hairs, with grooves along their length. Their lines range from pale green to yellow-green. Compound leaves split into fine parts, giving a fine texture. Leaves grow in turn along the stems, not in pairs. They get smaller near the top of the plant. Their thin parts help explain the name fir leaf celery.

Small white flowers have a pink tint and grow in umbels. In these groups, flower stalks spread from a shared point. NC State lists a long bloom season in summer and fall. Each flower is less than half a millimetre across. The fruit is a schizocarp and holds two seeds. Young fruits start pale green, then turn brown and drop. New plants can sprout from mid-spring through mid-autumn. Several rounds of plants may grow in one year. Young plants can look much like young wild carrots.

When grown in gardens, this plant needs full sun. It likes moist ground and grows in clay, loam, or sand. It also copes where water often stands on the ground. This includes plots that people water to grow plants. Wild records show it in both wet and dry sites. It grows fast and seeds itself with ease. These traits make it a troublesome garden weed. Plants can escape beds and spread into lawns or nearby ground. NC State warns that it may become invasive in some settings. Its fine leaves and long bloom season add visual interest. Yet growers need to watch its spread.

People gather wild plants for food and medicine. Some use the leaves in place of parsley. The leaves may have a harsh taste. These uses do not prove that it is safe to eat. Useful Tropical Plants reports that it is toxic to mammals and urges care. That source also records leaf use in Ethiopian folk medicine. People get an essential oil from the plant for medicinal use. These reports describe folk uses, not proof of safe treatment.