Rose family (Rosaceae)
Description: This perennial shrub is 2-5' tall, forming arching woody canes. First-year canes produce leaves that are palmately compound (usually 5 leaflets), while second-year canes produce trifoliate leaves (3 leaflets). First-year canes are infertile, while second-year canes bear flowers and fruit. The latter die down after bearing fruit, but they often start new canes vegetatively when their tips touch the ground. Young canes are light green, stout, and rather angular, but they later become red, reddish brown, or black. Stout prickles occur along the sides of the canes; these prickles are usually curved, rather than straight.
The compound leaves of first-year canes span up to 6" long and 6" across (excluding their petioles). The terminal leaflet is larger than the lateral leaflets; it is up to 3" long and 2½" across (less than twice as long as its width). Each terminal leaflet is ovate to oval in shape, rounded or cordate at the base, and coarsely serrated along its margins; the lateral leaflets are similar, except they are more slender in shape. At the base of each terminal leaflet, there is a conspicuous basal stalklet (petiolule) about ½" long, while the lateral leaflets are sessile, or nearly so. On the upper surface, each leaflet is medium green and either hairless or sparsely hairy; on the lower surface, each leaflet is light green and finely pubescent, especially along the veins. The petioles of the compound leaves are up to 4" long, pale green, and either hairless or sparsely pubescent; there are often 1-2 tiny curved prickles along the length of each petiole. The leaflets of second-year canes are slightly smaller in size than those of the first-year canes, and their terminal leaflets are more slender than the terminal leaflets of the latter. Otherwise, the leaflets of both types of canes are very similar to each other. Second-year canes bear short corymbs of flowers spanning about 2-4" across. Each flower is about 1" across, consisting of 5 white petals, 5 light green sepals, a cluster of light green pistils, and numerous stamens. The petals are oblanceolate in shape and rather wrinkled in appearance; they are much longer than the slightly pubescent sepals. At the base of the pedicel of each flower, there is either a stipule-like or leafy bract of varying size; the flowers are often partially hidden by these bracts. The blooming period of this blackberry occurs during late spring to early summer, lasting about 3 weeks. The flowers are replaced by a juicy fruits (compound drupes) that are globoid-ovoid in shape and up to ¾" long. The fruits become black at maturity during mid- to late summer; they have a pleasant sweet-tart flavor, sometimes with a slightly bitter aftertaste. Each drupelet within a fruit contains a single seed. The root system is woody and branching. Loose colonies of plants are often formed from vegetative propagation of the canes.
Cultivation: The preference is full or partial sun, moist to dry-mesic conditions, and soil containing loam, clay-loam, or some rocky material. The size of the fruit is strongly influenced by the amount of precipitation during the first half of summer.
Range & Habitat: The native Pennsylvania Blackberry is fairly common and it can be found throughout Illinois (see Distribution Map). Habitats include woodland openings, woodland edges, savannas, thickets, weedy meadows, and fence rows. This shrub is typically found in areas with a history of disturbance, although it is intolerant of regular mowing.
Faunal Associations: This species and other blackberries (Rubus spp.) are important to many kinds of wildlife. The nectar and pollen of the flowers attract many kinds of insects, including long-tongued and short-tongued bees, wasps, bee flies, butterflies, and skippers. The larvae of many moths feed on the leaves and flowers, or bore through the canes (see Moth Table). Other insects that feed on various parts of blackberries include several leaf beetles, larvae of long-horned beetles, stinkbugs, aphids, sawfly larvae, and others (see Insect Table). The fruit is an important source of food to many songbirds and upland gamebirds (see Bird Table). Many mammals feed on the fruit of blackberries as well, including the Deer Mouse, White-Footed Mouse, Jumping Mouse, Eastern Chipmunk, Fox Squirrel, Gray Squirrel, Red Squirrel, Red Fox, Raccoon, Striped Skunk, and Black Bear. White-Tailed Deer and Cottontail Rabbits feed on the leaves and twigs. The prickly canes and leaves of blackberries also provide protective cover for small mammals and birds.
Photographic Location: A grassy meadow near Urbana, Illinois.
Comments: The different species of blackberry (Rubus spp.) can be difficult to identify and different authorities don't always agree on their taxonomic classification. Pennsylvania Blackberry can be distinguished from other blackberry species by one or more of the following characteristics: 1) its terminal leaflets are no more than twice as long as they are across, 2) the hairs on its flowering corymbs are non-glandular, rather than glandular, 3) its corymbs of flowers are short and often partially hidden by leafy bracts, and 4) at least some of its floral bracts are large and leafy, rather than small and stipule-like. Compared to Rubus spp. that are raspberries, Pennsylvania Blackberry usually has larger flowers (about 1" across) and its compound drupes do not detach cleanly from their receptacles. Some taxonomists (e.g., Mohlenbrock, 2002) divide Pennsylvania Blackberry into two species: Rubus pensilvanicus and Rubus frondosus (Leafy-Flowered Blackberry). According to this taxonomic classification, the floral bracts of Leafy-Flowered Blackberry are all relatively large and leafy in appearance, whereas Pennsylvania Blackberry has a mixture of small stipule-like bracts and larger leafy bracts in its corymbs. In addition, the terminal leaflets of sterile canes are rounded at their bases for Pennsylanvia Blackberry, whereas for Leafy-Bracted Blackberry they have cordate (indented) bases. However, in the field, it is not uncommon to encounter shrubs that display mixed characteristics. As a result, Leafy-Flowered Blackberry can be considered a variant of Pennsylvania Blackberry.