Citrus family (Rutaceae)
Description: This native shrub is up to 20' tall with an irregular rounded crown, forming a central trunk up to 6" across. Sometimes multiple branches are produced from the ground, instead of a trunk. The bark of the trunk and larger branches is grey and slightly rough. Smaller branches have bark that is more smooth and gray-brown.
Alternate trifoliate leaves are produced on new stems that are green, terete, and usually hairless. The leaflets are 2-4" long and 1-2" across; they are narrowly ovate to ovate, smooth or slightly toothed along their margins, and sessile. The leaflet upper surfaces are medium to dark green, hairless, and shiny, while the lower surfaces are pale green and hairless (rarely pubescent). The bases of the leaflets are wedge-shaped, while their tips are slender and pointed. The petioles of the trifoliate leaves are light green, terete, hairless, and about 2-6" long. Occasionally, umbel-like panicles of flowers are produced that are 2-3" across. Wafer Ash is monoecious, often producing male, female, and perfect (bisexual) flowers on the same shrub. Regardless of gender, individual flowers are a little more than ¼" across. Perfect flowers have 4-5 petals, 4-5 sepals, 4-5 stamens, and a single flattened pistil that is green and obcordate-orbicular in shape. The petals are whitish or yellowish green and narrowly lanceolate-oblong. Male flowers lack the central pistil, while female flowers lack stamens. The slender pedicels of the flowers are light green and hairless. The blooming period occurs during the late spring and lasts about 2 weeks. Each flower with a pistil develops a flattened fruit that is broadly winged along its margins and about ¾–1" across. The winged margins of the fruit have a reticulated network of fine veins, while its center contains 2-3 seeds. Immature fruits are green, but they become light brown at maturity. The root system is woody and branching. Vegetative offsets from underground runners are not produced.
Cultivation: Wafer Ash is typically found in full sun to light shade, mesic to dry conditions, and rocky or sandy soil. This shrub may fail to flower if it receives too much shade.
Range & Habitat: Wafer Ash is widely distributed and occasional in Illinois (see Distribution Map). Habitats included mesic to upland deciduous woodlands, woodland edges and openings, mesic to upland savannas, rocky bluffs, thickets, stabilized sand dunes with woody vegetation, limestone glades, and fence rows. This shrub can be found in high quality to somewhat degraded habitats.
Faunal Associations: The flowers attract small bees, wasps, flies and ants. These floral visitors feed on the nectar of the flowers primarily, although some small bees also collect pollen. The caterpillars of the butterfly Papilio cresphontes (Giant Swallowtail) feed on the leaves of Wafer Ash; this is one of the few food plants of this species in Illinois. Another specialist feeder is the thrips Neohydatothrips pulchellus, which sucks juices from the leaflet undersides. Other insects that feed on Wafer Ash include the caterpillars of the moth Yponomeuta atomocella (Brown-Bordered Ermine Moth) and the larvae of the Scolytid beetle Phloeotribus scabricollis, which bore into the bark and wood. White-Tailed Deer probably don't browse on the leaves and twigs to any significant extent, as they have an unpleasant scent and bitter taste.
Photographic Location: Edge of a restored prairie at Meadowbrook Park in Urbana, Illinois.
Comments: Perhaps the most attractive feature consists of the wafer-like fruits, which resemble the samaras of Elm trees (Ulmus spp.). Otherwise, this rather unique shrub does not attract much attention to itself. Notwithstanding its common name, Wafer Ash is not one of the true ashes (Fraxinus spp.), which are members of the Olive family (Oleaceae). Another common name of this shrub is Hop Tree, because it was used as a substitute for hops in brewing beer. Different varieties of this shrub have been described across its wide range in the United States, but most specimens in Illinois correspond to the typical variety.