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.=