Hoary cress, aka whitetop (Cardaria draba), is a deep-rooted perennial introduced from Europe. Whitetop reproduces from seeds and also will send up new shoots from its roots, which spread horizontally in all directions. Even worse, it can reproduce from root segments. Highly competitive against other plants, whitetop will rapidly overrun a field or pasture unless it is aggressively eradicated – a noxious weed of the first order that is very difficult to control.
Mature whitetop is between 8″ and 24″ in height. The leaves are broadly oval to lance shaped and can be smooth or irregularly toothed. Small hairs give the plant a soft and hazy appearance. The leaves on the bottom of the stem have small stalks while those nearer the top of the stem are stalkless and have earlike lobes that clasp the stem.
The white flowers are borne on slender stalks radiating from the stem and give the plant a flat-topped appearance. The tiny petals are broad at the top narrowing toward the base.
The fruits are inverted heart-shaped pods that terminate in a beak. There are usually two oval, slightly flat, dark reddish-brown seeds – one in each of the two valves in the pod.
Whitetop grows in alkaline, disturbed soils. When it blooms in early spring a thick stand of whitetop can resemble a blanket of snow on the ground. A field overrun with whitetop does look pretty. It can be toxic to livestock if too much is ingested, however, animals will not eat whitetop if there is other sufficient forage.
Unfortunately whitetop occurs throughout our area (Northeast California) and I can even find it in neighboring pastures. (Leonard works VERY hard to keep our property free of whitetop and other noxious weeds.) These pictures were taken in McArthur Swamp (Shasta County CA). Whitetop – a pretty plant but a bane to farmers and ranchers.