9. Boechera Á. Löve & D. Löve
Plants biennial or perennial herbs (sometimes woody at the base elsewhere), terrestrial.
Stems erect, ascending or rarely spreading, usually branched. Leaves alternate
and basal, the basal ones often forming rosettes, sometimes absent at flowering
time, variously shaped and divided, the bases of the stem leaves clasping or
not, rarely petiolate, often pubescent with unbranched or forked hairs (with
stalked, more or less stellate hairs elsewhere), rarely glabrous or with
unbranched hairs only. Inflorescences racemes or panicles, the flowers not
subtended by bracts. Sepals erect or ascending. Petals not lobed; white, pink,
or purple. Styles absent or 0.5–2.0 mm long (rarely longer elsewhere).
Stigma entire. Fruits more than 10 times as long as wide, slightly to strongly
flattened parallel to the septum, dehiscing longitudinally by the valves
breaking off without coiling, each valve usually with a midnerve extending the
full length or rarely only near the base. Seeds in 1 or 2 rows in each locule,
winged or rarely wingless. About 65 species, North America.
Extensive molecular and cytological studies (summarized in Al-Shehbaz, 2003)
strongly support the recognition of Boechera as a genus not closely
related to Arabis. All species of Arabis have chromosome numbers
based on x=8, whereas all species of Boechera have x=7. The morphological
differences between the two genera are discussed in that paper.