Rose family (Rosaceae)
Description: This herbaceous perennial wildflower is about 1-2' tall. Alternate compound leaves occur primarily along the lower half of each hairy stem. These leaves are odd-pinnate; they are up to 8" long and 2" across. The lower leaves have 5-7 leaflets, while the sessile upper leaves have 3 leaflets. The terminal leaflet is much larger than the lateral leaflets. The leaflets are coarsely serrated, slightly hairy, rough-textured, and medium green; the terminal leaflet is sometimes divided into 3 lobes. In addition to these leaflets, the lower leaves have tiny secondary leaflets that are inserted between the lateral leaflets.
The upper stems terminate in nodding cymes of flowers. The branches of each cyme are dark purple and very hairy. Each flower is ¾–1" across, consisting of 5 dull red to pale purple petals, 5 dark purple sepals, numerous stamens with yellow anthers, and numerous pistils in the center. Sometimes the inner sides of the petals are pale yellow; regardless of color, they are conspicuously veined. The hairy sepals are ovate in shape; they are about as long as the petals. Between each pair of sepals, there is a linear bract that is dark purple and hairy. The blooming period occurs from late spring to mid-summer and lasts about 1-2 months. Each pistil is replaced by a flattened achene with a long persistent style; the style is hooked toward its tip and often pubescent. The root system is fibrous and rhizomatous. Dense clumps of plants are often formed from the rhizomes.
Cultivation: The preference is partial to full sun, wet to moist conditions, and cool to mild summer temperatures. Various kinds of soil are tolerated.
Range & Habitat: Water Avens is restricted to northern Illinois, where it is rare and native (see Distribution Map). Because this species has not been observed in natural areas of the state for several decades, it may be extirpated because of destruction or degradation of habitat. Water Avens has a circumboreal distribution in North America, Europe, and Asia; northern Illinois lies at its southern range limit. Habitats include White Cedar fens (in Kane County), bogs, marshes, and soggy meadows. This species is sometimes cultivated in gardens.
Faunal Associations: According to Mueller (1873/1883), the flowers produce both nectar and pollen; they are pollinated primarily by bumblebees. Mueller also observed honeybees, long-beaked Syrphid flies (Rhingia sp.), and Sap beetles (Nitulidae) visiting the flowers for nectar or pollen. Because the achenes have persistent styles with hooked or jointed tips, it is possible that they are distributed by birds or mammals.
Photographic Location: A flower garden at the University of Illinois Arboretum in Urbana, Illinois.
Comments: This is one of the more showy species in the genus. Other Geum spp. (Avens) have smaller flowers that are white or yellow. An exception is Geum triflorum (Prairie Smoke), which has nodding red to purple flowers. Unlike Water Avens, the petals of Prairie Smoke are mostly hidden by the sepals. The achenes of Prairie Smoke have long plumose styles that are distributed by the wind. In contrast, the achenes of Water Avens have styles that are jointed or hooked; they are probably distributed by animals, as noted above. Prairie Smoke typically occurs in dry gravelly prairies, while Water Avens is found in various wetland habitats. Another common name of Geum rivale is Purple Avens.