Order 10. CRUCÍFERÆ. (Mustard Family.)
Herbs, with a pungent watery juice and cruciform tetradynamous flowers; fruit a silique or silicle.—Sepals 4, deciduous. Petals 4, hypogynous, regular, placed opposite each other in pairs, their spreading limbs forming a cross. Stamens 6, two of them inserted lower down and shorter (rarely only 4 or 2). Pod usually 2-celled by a thin partition stretched between the two marginal placentæ, from which when ripe the valves separate, either much longer than broad (a silique), or short (a silicle), sometimes indehiscent and nut-like (nucumentaceous), or separating across into 1-seeded joints (lomentaceous). Seeds campylotropous, without albumen, filled by the large embryo, which is curved or folded in various ways: i.e. the cotyledons accumbent, viz., their margins on one side applied to the radicle, so that the cross-section of the seed appears thus o==; or else incumbent, viz., the back of one cotyledon applied to the radicle, thus o||. In these cases the cotyledons are plane; but they may be folded upon themselves and round the radicle, as in Mustard, where they are conduplicate, thus o>>. In Leavenworthia alone the whole embryo is straight.—Leaves alternate, no stipules. Flowers in terminal racemes or corymbs; pedicels rarely bracted.—A large and very natural family, of pungent or acrid, but not poisonous plants. (The characters of the genera are taken almost wholly from the pods and seeds; the flowers being nearly alike in all.)
SERIES I. Pod 2-celled, regularly dehiscent by 2 valves.
[*] Pod compressed parallel to the broad partition. Seeds flat or flattish, orbicular or oval; cotyledons accumbent or nearly so.
[+] Pod large, oblong-elliptical, valves nerveless. Seeds in 2 rows. Flowers yellow.
1. Selenia. Leaves pinnatisect. Raceme leafy-bracteate. Seeds winged.
[+][+] Pod linear; valves nerveless. Seeds in one row. Flowers yellow only in n. 3.
2. Leavenworthia. Seed winged; embryo straight or nearly so. Annual; stem often scapose, 1–few-flowered.
3. Dentaria. Stem naked below, 2–3-leaved. Pod coriaceous, with thick placentas, long-styled. Seeds wingless; cotyledons thick, very unequal.
4. Cardamine. Stem leafy. Pod coriaceous, with thick placentas. Seeds wingless; cotyledons flattened, equal.