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, shrubs, or trees, with alternate (in some exotic genera opposite), simple or compound leaves, and regular perfect or rarely polygamo-dioecious flowers. Stipules commonly present, sometimes large. Calyx free from or adnate to the ovary, 5-lobed (rarely 4-9-lobed), often bracteolate. Disk adnate to the base of the calyx. Petals equal in number to the calyx-lobes, distinct, or none. Stamens usually numerous, distinct; anthers small, 2-celled. Carpels 1-∞, distinct, or adnate to the calyx. Ovary 1-celled or rarely imperfectly 2-celled; style terminal or lateral. Ovules 1, 2, or several, anatropous. Fruit various, mostly follicles or achenes; endosperm none, or rarely copious.
A family comprising about 75 genera and more than 1200 species, of wide geographic distribution.
A. Fruit of 1-5 dehiscent follicles.
* Carpels alternate with the sepals; stipules deciduous or none.
Carpels, if more than 1, united below; seeds with endosperm (Neillieae).
Carpels normally 5, distinct; seeds without endosperm (Spiraeeae).
Flowers perfect; shrubs with simple leaves.
Flowers dioecious; tall herbs with pinnately 2-3-compound leaves.
** Carpels opposite the sepals; stipules persistent (Sorbarieae).
Petals obovate or spatulate, imbricated; leaves pinnate.
Petals strap-shaped, convolute in the bud; leaves trifoliolate.
B. Fruit indehiscent, of achenes or drupelets.
* Carpels not enclosed in the fleshy calyx-tube (hypanthium).
I. Fruit of dry achenes.
Ovaries 2-ovuled (Ulmarieae).
Seed pendulous or ascending, borne in the ovary opposite to the base of the style.
Style articulated with the ovary; calyx-tube from campanulate to nearly flat (Potentilleae).
Style terminal or nearly so; ovule and seed pendulous.
Style lateral; ovule and seed ascending.
Herbs; achenes glabrous.
Achenes numerous; stamens about 20.
Receptacle not enlarged in fruit; petals yellow, obtuse or refuse.
Receptacle somewhat enlarged in fruit, spongy; petals red, acute or acuminate.
Leaves 3-foliolate; receptacle much enlarged in fruit.
Receptacle not pulpy; petals yellow.
Receptacle very pulpy: petals white or pinkish.
Achenes 10-15; stamens 5; leaves 3-foliolate.
Shrubs; achenes hairy.
Style filiform; leaves 3-foliolate.
Style club-shaped; leaves pinnate.
Style nearly basal; ovule and seed ascending.
Stamens numerous; flowers bracteolate; leaves pinnate.
Stamens 5; flowers ebracteolate; leaves 2-3-ternately compound.
Style not articulated with the ovary; calyx-tube urn-shaped or cup-shaped, contracted at the
throat or mouth.
Style nearly basal; inflorescence cymose; petals none (Alchemilleae).
Perennial herbs; stamens 4, alternate with the sepals.
Small annual herbs; stamen 1, opposite a sepal, rarely 2-5.
Style terminal; inflorescence spicate, racemose or capitate (Sanguisorbeae).
Calyx-tube not prickly; petals none.
Stamens 2-4, not declined; pistil 1.
Perennial herbs; stigma papillose; leaflets toothed.
Annual or biennial herbs; stigma brush-like; leaflets pectinate-pinnatifid.
Stamens of staminate flowers numerous, declined; pistils 2.
Calyx-tube and fruit prickly; petals present, yellow.
Seed erect, basal.
Style wholly deciduous (Colurieae).
Style persistent in whole or in part.
Calyx-tube hemispheric to turbinate, persistent; herbs (Dryadeae).
Calyx-lobes and petals 5; leaves pinnate.
Styles jointed, the upper part deciduous.
Styles not jointed, wholly persistent, mostly plumose.
Calyx-lobes and petals 8 or 9; leaves simple; styles plumose.
Calyx-tube salver-shaped, the limb deciduous; the tube persistent, investing the achene;
shrubs or trees (Cercocarpeae).
2. Fruit of fleshy or nearly dry drupelets; ovary 2-ovuled (Rubeae).
Drupelets very pulpy.
Drupelets nearly dry, enclosed by the calyx.
** Carpels enclosed in the fleshy calyx-tube (Roseae).