12a. Stems gray with a close fine p.u.b.escence =Tansy Mustard, Sisymbrium canescens.=

12b. Stems green =Tansy Mustard, Sisymbrium canescens var. brachycarpon.=

13a. Pod short, not more than 3 times as long as wide (coa.r.s.e plants, preferring wet or sandy ground; flowers in summer) (Yellow Cress) --14.

13b. Pod elongated, more than 4 times as long as wide --17.

14a. Stems creeping, with erect or ascending branches; flowers about 8 mm. wide =Yellow Cress, Radicula sylvestris.=

14b. Stems erect or ascending (3-10 dm. high); flowers about 4 mm.

wide --15.

15a. Pods about twice as long as the pedicels =Yellow Cress, Radicula obtusa.=

15b. Pods about as long as the pedicels, or shorter than them --16.

16a. Plant glabrous or minutely p.u.b.escent =Yellow Cress, Radicula pal.u.s.tris.=

16b. Plant hirsute =Yellow Cress, Radicula pal.u.s.tris var. hispida.=

17a. Petals 7 mm. long or more; pod terminating in a conspicuous beak (coa.r.s.e, weedy plants, 3-12 dm. high, blooming in summer) --18.

17b. Petals of smaller size; pod not terminating in a conspicuous beak --24.

18a. Upper stem-leaves clasping at the base =Rutabaga, Bra.s.sica campestris.=

18b. Upper stem-leaves not clasping --19.

19a. Pod tipped with a slender cylindrical beak whose base is much narrower than the pod --20.

19b. Pod gradually narrowed at its tip into a stout, flattened or angled beak --22.

20a. Leaves oblanceolate, rather regularly pinnatifid, the terminal segment about the same size as the lateral ones =Sand Rocket, Diplotaxis muralis.=

20b. Leaves broad, irregularly pinnatifid especially below the middle, with a large terminal segment --21.

21a. Beak of pod 3-4 mm. long =Black Mustard, Bra.s.sica nigra.=

21b. Beak of pod 5 mm. long or more =Indian Mustard, Bra.s.sica juncea.=

22a. Leaves dentate or lobed =Charlock, Bra.s.sica arvensis.=

22b. Leaves deeply pinnatifid --23.

23a. Pod dehiscent when ripe by two valves, tipped with a flat or angled beak =White Mustard, Bra.s.sica alba.=

23b. Pod indehiscent, with spongy cross-part.i.tions between the seeds, tipped with a conical beak =Wild Radish, Rapha.n.u.s raphanistrum.=

24a. Terminal segment of the princ.i.p.al leaves much larger than the lateral segments; flowers in spring and summer --25.

24b. Terminal segment of the princ.i.p.al leaves equaling or smaller than the lateral ones (5-10 dm. high; pods very long and slender; flowers in summer) =Sisymbrium, Sisymbrium altissimum.=

25a. Flowers about 3 mm. wide; pods erect and closely appressed to the stem (3-9 dm. high; weed blooming in summer) (Hedge Mustard) --26.

25b. Flowers about 7 mm. wide; pods spreading or ascending (3-6 dm.

high; flowers in spring) (Winter Cress) --27.

26a. Pods p.u.b.escent =Hedge Mustard, Sisymbrium officinale.=

26b. Pods glabrous =Hedge Mustard, Sisymbrium officinale var. leiocarpum.=

27a. Lateral leaf-segments 5-8 pairs on the princ.i.p.al leaves =Winter Cress, Barbarea verna.=

27b. Lateral leaf-segments 1-4 pairs on the princ.i.p.al leaves --28.

28a. Flowers bright yellow, in racemes; pods spreading or ascending =Winter Cress, Barbarea vulgaris.=

28b. Flowers pale yellow, in corymb-like cl.u.s.ters; pods erect and somewhat appressed =Winter Cress, Barbarea stricta.=

29a. Princ.i.p.al stem-leaves compound or deeply lobed (the uppermost or bracteal leaves may be simple) --30.

29b. Princ.i.p.al stem-leaves entire, dentate, serrate, or sometimes shallowly lobed or none (the basal leaves, at the surface of the ground, may be deeply lobed or compound) --42.

30a. Leaves ternately divided or compound (2-5 dm. high; flowers in spring) (Toothwort) --31.

30b. Leaves pinnately divided or compound --33.

31a. Leaf-segments lanceolate or narrowly oblong =Toothwort, Dentaria laciniata.=

31b. Leaf-segments ovate or ovate-oblong --32.

32a. Stem-leaves 2, opposite or nearly opposite =Toothwort, Dentaria diphylla.=

32b. Stem-leaves 2-5, alternate =Toothwort, Dentaria maxima.=

33a. Plants growing in water, or in mud near water (spring and summer) --34.

33b. Plants of dry or moist soil --35.

34a. Aerial leaves distinctly compound, with 3-11 leaflets =Water Cress, Radicula nasturtium-aquatic.u.m.=

34b. Aerial leaves merely serrate to pinnatifid; the submerged leaves, if present, dissected =Lake Cress, Radicula aquatica.=

35a. Flowers 5 mm. broad, or less --36.

35b. Flowers 6 mm. broad, or more --39.

36a. Stem-leaves irregularly pinnatifid or lobed; pod about as broad as long (2-4 dm. high; flowers in summer) =Garden Cress, Lepidium sativum.=