Heart-Leaved Willow is dioecious, producing staminate (male) catkins and pistillate (female) catkins on separate shrubs. These catkins are produced a little before or during the development of first-generation leaves during the spring. Staminate catkins are ¾-1½" long. Each floret of these catkins has 2 stamens. At the base of these stamens, there is a single finely hairy bract that is brown to black and a minute cylindrical gland. Pistillate catkins are 1-2½" long. Each floret of these catkins has a single lanceoloid ovary (4-6 mm. long) that is glabrous and a short style with divergent stigmata on top; there is a short pedicel underneath the ovary. Beside the pedicel, there is a single finely hairy bract that is brown to black and a minute cylindrical gland. Blooming period lasts about 1-2 weeks during the spring. Afterwards, the female florets are replaced by seed capsules that split open to release tiny cottony seeds. These seeds are distributed by the wind. The root system is shallow, woody, and branching. This shrub spreads by reseeding itself.
Cultivation: The preference is full to partial sun, wet to moist conditions, and soil containing loam, calcareous sand, or gravel. Occasional flooding is tolerated if it is temporary. The seeds remain viable for only 1-2 weeks; they require moist ground to germinate. It is also possible to propagate this shrub by sticking a broken-off stem into the ground during the spring.
Range & Habitat: The native Heart-Leaved Willow is occasional throughout Illinois (see Distribution Map). Habitats include open woodlands with immature trees, soggy meadows along rivers, edges of sandy swales and sloughs, fens, and ditches. This shrub is found in both degraded and higher quality wetlands.
Faunal Associations: The nectar and pollen of the florets of this willow can attract many insects, especially bees and flies. Several Andrenid bees (Andrena spp.) are specialist pollinators (oligoleges) of willows. The caterpillars of Satyrium acadicum (Acadian Hairstreak), Satyrium liparops strigosum (Striped Hairstreak), Limenitis archippus (Viceroy), Limenitis arthemis astyanax (Red-Spotted Purple), Nymphalis antiopa (Mourning Cloak), and Nymphalis vau-album j-album (Compton Tortoiseshell) feed on the foliage of these shrubs. Other insect feeders include the caterpillars of Catocala relicta (White Underwing), Micrurapteryx salicifoliella (Willow Leaf Miner), Nycteola metaspilella (Little Willow Sister), and many other moths (see Moth Table); the wood-boring larvae of Agrilus politus (Common Willow Agrilus), Cryptorhynchus lapathi (Poplar & Willow Borer), and similar beetles (see Wood-Boring Beetle Table); Chrysomela knabi (American Willow Leaf Beetle), Disonycha alternata (Striped Willow Flea Beetle), and other leaf beetles (see Leaf Beetle Table); Cavariella aegopodii (Carrot-Willow Aphid), Tuberolachnus salignus (Giant Willow Aphid), and other aphids; Lopidea salicis (Willow Plant Bug) and other plant bugs; the larvae of Nematus ventralis (Willow Sawfly) and other sawflies; Microcentrum retinervis (Angular-Winged Katydid) and many other insects. For a more complete listing of these species, see the Insect Table. Vertebrate animals also use willows as a food source and to provide cover. Among birds, the Ruffed Grouse, Northern Pintail, Mallard, and White-Crown Sparrow eat the buds or catkins. The Yellow Warbler, Warbling Vireo, Philadelphia Vireo, and Rusty Grackle use willows as nesting sites. Among mammals, the White-Tailed Deer and Elk browse on the stems and leaves, while the Beaver gnaws on the bark and wood. The leaves of willows are consumed by some turtles, including Chelydra serpentina (Snapping Turtle) and Clemmys insculpta (Wood Turtle).
Photographic Location: Photographs of the sapling were taken at a ditch in Urbana, Illinois, while the photograph of a more mature shrub was taken at the Indiana Dunes National Lakeshore in NW Indiana.
Comments: Heart-Leaved Willow has an unstable taxonomic history and some authorities regard it as a variation of another species, Salix eriocephala (Missouri River Willow). Following Mohlenbrock (2002), this willow is considered a distinct species, Salix rigida. Generally, Heart-Leaved Willow differs from the Missouri River Willow by always remaining a shrub (12' or less) and having leaves that are slightly more wide. Furthermore, it often has woody stems that are yellowish tan, instead of reddish brown. Heart-Leaved Willow is also closely related to another shrubby willow, Salix glaucophylloides (Blue-Leaf Willow). Blue-Leaf Willow has leaves that are slightly more wide and more coarsely toothed than those of Heart-Leaved Willow, but these differences are not dramatic. Occasionally these and other willows hybridize, making identification even more difficult than it already is. Heart-Leaved Willow has been referred to as Salix cordata in the past, but this scientific name refers to another willow species further to the east that has much hairier stems and leaves.