Very variable in foliage, finely stellate-pubescent and usually cinereous-villous with larger single hairs; caudex stout, branched. Leaves soft in texture, usually deeply pinnatifid with 2-several pairs of linear to obovate, obtuse segments. Stems several, 1—6 inches high, racemes at first dense and corymbose, becoming elongated in fruit. Flowers white with exserted broad rounded petals ⅛ of an inch or more long; pods usually lanceolate, tapering to each end. On alpine summits through the Rockies; not common; flowering in June and July. [Sidenote: =Sisymbrium altissimum= L. Tall _Hedge Mustard._] Erect, 2—4 feet high, freely branching, smooth or nearly so. Lower leaves runcinate-pinnatifid, petioled, the lobes lanceolate, often auriculate; upper leaves smaller, short petioled, or usually sessile, very deeply pinnatifid, the lobes linear or lanceolate, dentate or entire, the uppermost often reduced to linear, entire bracts. Flowers pale yellow, ¼ of an inch broad on slender spreading pedicels, pods very narrowly linear, divergent, 2—4 inches long. At the lower elevations throughout the region as a weed, especially on the line of the railway, flowering in July. [Sidenote: =Sophia intermedia= Rydb. _Western Tansy-Mustard._] Stems 1—2 feet high, sparingly greyish-puberulent, especially below, or sometimes nearly smooth, often glandular above; hairs more or less stellate. Leaves twice or thrice-pinnatifid, the primary divisions oblanceolate or obovate, divided to near the midrib into linear or linear-oblong segments, sparingly puberulent. Raceme rather long, flowers small, less than ⅛ of an inch high; petals yellow; peduncles diverging sometimes nearly at right angles; pod club-shaped. Common throughout the Rockies in open places at the lower altitudes, flowering in June and July. [Sidenote: =Braya humilis= (Meyer) Robinson. _Northern Rock-cress._] Erect 4—10 inches high, branching below, sparingly hairy. Leaves spatulate or oblanceolate, the lower obtuse, 1—2 inches long, narrowed into a petiole, sharply dentate or rarely entire, the upper smaller, narrower, often acute. Flowers white or pink ⅛ of an inch or more broad, pedicels erect, ¼ of an inch long in fruit; pods nearly terete, narrowly linear, ½—¾ of an inch long, valves finely nerved. In moist gravelly or stony ground throughout the Rockies at the lower altitudes, flowering in June. [Sidenote: =Roripa Nasturtium= (L.) Rusby. _Water-cress._] Aquatic, smooth, branched, floating or creeping, rooting from the joints. Leaves odd-pinnate of 3—9 segments, the terminal one larger than the lateral, all obtuse, ovate or oval or the terminal one nearly orbicular. Racemes elongated in fruit; flowers white, ⅛ of an inch or more broad; pod ½—1¼ inches long, spreading and slightly curved upwards, on pedicels of about their length. In ditches and shallow pools through the Rockies, especially abundant at Banff in the warm water at the outlet from the Basin; flowering through June and July.