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, or sometimes shrubby plants, with alternate or opposite leaves, and axillary or terminal, solitary, spicate or racemose flowers. Calyx-tube linear, produced beyond the ovary, the limb 4-parted, deciduous. Petals 4, mostly obovate or obcordate. Stamens 8; anthers oblong or linear, short. Ovary 4-celled; united styles slender or filiform; stigma club-shaped or 4-lobed; ovules numerous. Capsule narrow, elongated, 4-sided, 4-celled, loculicidally dehiscent by 4 valves. Seeds small, numerous, with a tuft of hairs (coma) at the summit. [Greek, upon a pod, flower and pod appearing together.]
About 75 species. of wide geographic distribution, most abundant in temperate regions. Besides the following, about 35 others occur in the western and northwestern parts of North America. Type species: Epilobium hirsutum L.
Stigma deeply 4-lobed; flowers large.
Stigma entire, or merely notched.
Flowers white; leaves usually denticulate.
Flowers violet; leaves mostly entire.
Leaves linear or lanceolate, entire or nearly so.
Plants crisp-pubescent or canescent.
Leaves sessile, not revolute-margined.
Leaves petioled, very narrow, acute, revolute-margined.
Plants glandular-pubescent, at least above.
Densely pubescent throughout; leaves sessile.
Glandular-pubescent above; leaves petioled.
Leaves lanceolate or ovate, serrate.
Leaves lanceolate, acute or acuminate; stems solitary.
Seeds obconic, beakless; coma reddish; leaves narrowly lanceolate.
Seeds ellipsoid, short-beaked; coma white; leaves oblong-lanceolate to ovate-lanceolate.
Leaves ovate, thin, obtuse, or the upper acutish; stems tufted.