This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", 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, some species slightly woody, with alternate or opposite entire lobed or dissected leaves. Flowers perfect, corymbose-capitate, cymose or paniculate, regular, or nearly regular. Calyx inferior, persistent, tubular or campanulate, 5-cleft, the lobes or teeth slightly imbricated. Corolla gamopetalous, funnel form, saucer-shaped, campanulate or rotate, the limb 5-parted, convolute in the bud. Stamens 5, inserted on the tube of the corolla and alternate with its lobes; filaments slender or filiform; anthers ovate, oblong or linear, versatile, 2-celled, the sacs longitudinally dehiscent. Ovary superior, mostly 3-celled; ovules 2-00 in each cavity, amphitropous; style simple filiform; stigmas 3, linear. Capsule mostly loculi-cidally 3-valved. Seeds various, sometimes winged, sometimes enveloped in mucilage and emitting spiral tubes when wetted; endosperm abundant; embryo straight; cotyledons flat; radicle inferior.
About 20 genera and over 200 species, most abundant in western America. Calyx distended and at length ruptured by the ripening capsule. Calyx scarious between the lobes.
Corolla salverform; leaves opposite, entire.
Seeds not mucilaginous when wetted; mostly perennials with large flowers; leaves opposite.
Seeds mucilaginous when wetted; annuals; floral leaves alternate; flowers small.
Corolla funnelform, tubular, salverform or campanulate; leaves alternate or opposite.
Calyx not scarious between the lobes; leaves alternate, deeply cleft.
Calyx not distended nor ruptured by the capsule; leaves alternate. Calyx-teeth herbaceous, not spinulose-tipped. Stamens declined; leaves pinnate.
Stamens straight and leaves entire in our species.
Calyx-teeth spinulose-tipped; leaves pinnatifid.