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..
Tall perennial herbs, with alternate petioled pinnately divided stipulate leaves, and small white, pink or purple perfect flowers in large cymose panicles. Calyx 5-lobed. Petals 5, clawed. Stamens numerous, inserted on the flat or slightly concave receptacle; filaments narrowed at the base. Pistils about 10 (5-15), distinct; ovary 2-ovuled. Ripe carpels capsular, indehiscent, 1-seeded. Seed pendulous. [Latin, a hanging thread.]
About 10 species, natives of the north temperate zone. Besides the following, 2 others occur in northwestern America. Type species: Spiraea Filipendula L.
Lateral leaflets palmately 3-5-lobed; flowers pink or purple.
Lateral leaflets merely serrate, or slightly lobed; flowers white.
Ulmaria rubra Hill, Hort. Kew. 214. pl. 7. 1769.
Spiraea lobata Gronov.; Jacq. Hort. Vind. 1: 38. pl. 88. 1770.
Glabrous, stem branched, grooved, 2°-8° tall. Leaves large, green on both sides, the lower sometimes 3o long, pinnately 3-7-folio-late, commonly with smaller leaf-segments interposed or borne on the petiole; lateral leaflets sessile, opposite, palmately 3-5-lobed or 3-5-parted, the lobes acute, unequally serrate or incised; terminal leaflet larger, 7-9-parted; stipules serrate, persistent, 4"-8" long; flowers pink or purpie, fragrant, about 4" broad; capsules glabrous.
Spiraea Ulmaria L. Sp. Pl. 490. 1753. Ulmaria palustris Moench, Meth. 663. 1794. Ulmaria Ulmaria Barnhart, Bull. Torr. Club 21:
491. 1894. F. Ulmaria Maxim. Acta Hort. Petrop. 6: 251.
Stem branched, angular or grooved, 2°-4° tall. Leaves pinnately 3-9-foliolate, densely and finely white-downy beneath, green above, sometimes with several or numerous much smaller leaf-segments interposed between the leaflets or borne on the petiole; lateral leaflets sessile, opposite, ovate or ovate-lanceolate, acute or acuminate, serrate or sometimes slightly lobed, the terminal one larger and deeply 3-5-lobed, the lobes acute and serrate; stipules about 1/2' long; flowers white or greenish-white, fragrant.
Filipendula denudÓta (Presl) Rydb., differs in having the leaves green on both sides, and is established near Dover, Maine. It is also native of Europe and Asia.