Rorippa palustris aka Marshcress

Rorippa palustris is also known as marsh yellowcress. It belongs to Brassicaceae, the mustard family. Its native range spans the Northern Hemisphere's temperate lands. It also grows wild in tropical mountains. The RHS lists Britain and Ireland within its native range. Kew places it in temperate climates. Kew calls it an annual or a helophyte. A helophyte is a marsh plant. North Carolina State Extension calls it a winter annual weed. That source also notes its wide range across the United States. The RHS gives Nasturtium palustre as another name for it.

The plant starts with green leaves in a rosette. This is a cluster at the base of the plant. The leaves have deep lobes and a pinnate form. Their lobes lie on each side of a central axis. The lobes grow deeper as the plant ages. Upright flower stalks rise from the rosette, then branch. In pots, the plant often forms one main upright stem. This stem may branch only in the flower cluster. The term for this cluster is inflorescence. Plants can also form mounds with many branches. The leaves have no hairs; the stems have no scent. The sources give no mature height or spread.

The yellow flowers turn into seed pods shaped like cylinders. These pods, called siliques, hold many small, tan seeds. Short stalks hold the pods on marsh yellowcress. Each stalk measures about 0.04 feet [0.013 metres]. This trait helps tell it from southern yellowcress, Rorippa teres. The two species look alike, which can cause confusion. Southern yellowcress pods have no stalks or much shorter ones. The fruit tells them apart better than their overall shape.

Marsh yellowcress grows most often in moist sites. It can also grow in a wider range of settings. Seeds sprout in cool, moist soil in autumn or spring. These flushes of growth help explain why it is a weed. The sources give no light needs or hardiness zones. They give no garden uses or landscape benefits. The main garden problem they note is unwanted growth. North Carolina State Extension reports control with several preemergence herbicides. These weedkillers act before plants emerge. But it warns that evidence for their control rankings remains limited. No supplied source confirms edible parts or safety for people or pets. The sources name no specific pests or diseases.