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 (some tropical genera trees or shrubs) with simple entire leaves, and regular flowers in terminal or axillary clusters, in the following genera subtended by involucres of distinct or united bracts. Petals none. Calyx inferior, usually corolla-like, its limb campanulate, tubular or salverform, 4-5-lobed or 4-5-toothed. Stamens hypogynous; filaments filiform; anthers 2-celled, dehiscent by lateral slits. Ovary enclosed by the tube of the perianth, sessile or stipitate, I-celled, I-ovuled; ovule campylotropous; style short or elongated; stigma capitate. Fruit a ribbed, grooved or winged anthocarp.
About 25 genera and 350 species, of wide geographic distribution, most abundant in America.
Involucre of united bracts; pairs of leaves equal.
Involucre of separate bracts; pairs of leaves mostly unequal.
Wings or ridges of the fruit not completely encircling it.
Wings of the fruit completely encircling it.