This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs with basal or alternate or opposite leaves. Flowers perfect or polygamo-dioecious, solitary, racemose, cymose or paniculate. Calyx 5-lobed or 5-parted (rarely 4-12-lobed or parted), free, or adnate to the ovary, usually persistent. Petals usually 4 or 5, rarely none. Stamens equal in number or twice as many as the petals, in apetalous species as many or twice as many as the calyx-lobes, peri-gynous or epigynous; filaments distinct. Disk generally present. Carpels 1-several, often 2, distinct or united, mostly fewer than the stamens; styles as many as the carpels or cavities of the ovary. Fruit a capsule or follicle. Seeds commonly numerous; endosperm generally copious, fleshy; embryo small, terete.
About 90 genera and 650 species, of wide geographic distribution, mainly natives of the temperate zones, rare in the tropics.
Large herbs; leaves 3-ternate; flowers polygamous.
Small herbs; leaves simple, entire, toothed or cleft, or 3-foliolate.
Placentae axial; carpels equal or nearly so.
Calyx-tube only slightly developed, unchanged at maturity; or if slightly accrescent, then
flat or flattish and plants acaulescent.
Leaves opposite, except sometimes on flower-stalks.
Leaves alternate, sometimes all basal.
Corolla essentially regular, the petals about equal in length and shape.
Corolla irregular, except sometimes that of the terminal flower, three of the
petals with blades of an ovate-lanceolate or sagittate type, and two of them
narrower and longer.
Calyx-tube well-developed, and accrescent, at maturity longer than the lobes.
Plants without caudices, only producing annual flowering stems.
Plants with perennial leafy caudices, often with offsets, the flowering stem very differ-
ent from the caudex.
Leaves of the caudex with lobed blades, the margins poreless.
Leaves of the caudex with serrate blades, each tooth with an encrusted pore.
Calyx-lobes valvate; petals deciduous; seeds wingless.
Calyx-lobes imbricated; petals persistent; seeds winged.
♦Revised for this edition by Dr. John Kunkel Small.
Placentae almost basal; carpels very unequal.
Placentae parietal; carpels equal or nearly so.
Flowers in elongated racemes or panicles.
Petals entire or erose.
Petals pinnately cleft or parted.
Flowers solitary and axillary to leaf-like bracts or 2-4 together and each subtended by a