Rockcress

About rockcress
Rockcress is a common name used for three similar genera of flowering plants in the family Brassicaceae:

Arabis
Though traditionally recognized as a large genus with many Old World and New World members, more recent evaluations of the relationships among these species using genetic data suggest that there are two major groups within the old genus Arabis. These two groups are not each others closest relatives, so have been split into two separate genera. The Old World members all remain in the genus Arabis, whereas most of the New World members have been moved into the genus Boechera, with only a few remaining in Arabis.

The species are herbaceous annual or perennial plants, growing to 10-80 cm tall, usually densely hairy, with simple entire to lobed leaves 1-6 cm long, and small white four-petalled flowers. The fruit is a long, slender capsule containing 10-20 or more seeds.

Some species, notably A. alpina, are cultivated as ornamental plants in gardens. Many others are regarded as weeds.

Arabidopsis
Also known as "Thale cress", Arabidopsis (A-ra-bi-dóp-sis, rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (Arabidopsis thaliana), one of the model organisms used for studying plant biology and the first plant to have its entire genome sequenced. Changes in thale cress are easily observed, making it a very useful model.

Boechera
Boechera (rockcress) is a genus of the family Brassicaceae. It was named after the Danish botanist Tyge W. Böcher (1909-1983), who was known for his research in alpine plants, including the mustards Draba and Boechera holboellii. According to recent molecular based studies Boechera is closely related to the genus Arabidopsis which also includes the widely known model plant Arabidopsis thaliana. Until recently, members of this genus were included in the genus Arabis, but have been separated from that genus based on recent genetic and cytological data[1]. Unlike the genus Arabis (x=8) Boechera has a base chromosome number of x=7. Many taxa are triploid. Boechera is a primarily North American genus, most diverse in the western United States but its distribution range also includes Greenland and the Russian Far East. The genus is poorly known, and species within are difficult to separate morphologically though some clearly distinct species are known.

Most members of the genus are perennial plants with pubescent leaves with stellate trichomes, narrow curving fruits, and small white to purple flowers in elongated racemes. Relationships within the genus are unclear, and some eastern North American species, including Boechera laevigata, may belong to a clade distinct from the rest of the genus.