Flower:

Raceme up to 6 inches (6 to 15 cm) long at the tip of short lateral shoots along 1-year-old stems, each cluster with 4 to 16 flowers. Flowers are white, 1 to 1½ inches (2.5 to 4 cm) across with 5 rounded petals. In the center is a green cluster of many styles surrounded by a ring of numerous creamy white-tipped stamens.

Cupping the flower are 5 green sepals, broadly triangular, long-tapering to pointed or tail-like tip, the outer surface hairless or thinly covered in non-glandular hairs. Flower stalks are hairless to thinly hairy, sometimes with a few small, broad-based prickles.

Leaves and stems:

Leaves are alternate and palmately compound, the non-flowering first-year stems (primocanes) with 5 leaflets, the flowering second-year stems (floricanes) with 3 leaflets. Leaflets are generally elliptic, sharply toothed around the edges, hairless or nearly so. The terminal leaflet on primocanes is 3¾ to 5¾ inches (9.5 to 14.5 cm) long, up to about 3 inches (5.5 to 8 cm) wide, widest at or above the middle, rounded to heart-shaped at the base, the tip tapered to a long, extended or tail-like tip.

Leaf stalks are hairless, sometimes with a few small, weak, broad-based prickles. At the base of the compound leaf stalk is a pair of linear appendages (stipules) about ½ inch (to 12 mm) long. Stems are up to 6 feet (to 2 m) long, green to red or purple, hairless, initially erect but usually lean or arch over, not rooting at the tips, and die the second year after fruit matures. Prickles are small, weak, broad-based and widely spaced or lacking altogether.

Fruit:

Fruit is a round to cylindric cluster of fleshy drupelets, average ½ inch (9 to 16 mm) diameter, maturing from green to red to black, and are quite tasty.

Notes:

Smooth Blackberry is an uncommon species in Minnesota, where it reaches the western edge of its range in our eastern counties. It does not form large thickets like some other Rubus species do, but tends to be in small colonies or scattered plants, often growing with or near other Rubus. In Minnesota it's most often found in the part-shade of forest edges and clearings, occasionally on the rocky shore above Lake Superior.

Rubus is a large and difficult genus; both first year (non-flowering primocane) and second year (flowering/fruiting floricane) stems from the same plant may be necessary for a positive ID. Multiple species frequently grow together so stems from the same plant is recommended. Primocanes should be used for stem and leaf characteristics, floricanes mostly for just flowers and fruit. Characteristics to look for are the size and shape of the flower cluster as well as the flower, whether there are glandular and/or non-glandular hairs (on sepals, leaves, stalks and/or stems), whether there are any broad-based prickles or needle-like bristles, number of leaflets on the primocane and whether they are palmately or pinnately compound, whether canes are low-growing or trailing along the ground and/or root at the tip. In some species, the leaflet shape may also be relevant. Floricane leaves are frequently different from primocane leaves in shape and/or number of leaflets so are not a good substitute, and keep in mind that primocanes mature and tip-rooting occurs later in the season than peak flowering time.

Rubus canadensis is one of the easier species to identify, as it lacks any glandular hairs; prickles are broad-based, tend to be small and weak, and are widely spaced or absent altogether; leaves are hairless or nearly so; the flower cluster is a raceme with up to 16 flowers, and sepals are hairless to thinly hairy. Canes typically lean or arch over but do not root at the tips. Primocane leaves all have 5 leaflets, the terminal leaflet usually with a narrowed, extended tip (long-acuminate).

Rubus quaesitus is the only other Rubus species in Minnesota with a similar growth habit and has broad-based prickles, hairless leaves, and lacks glandular hairs, though occasionally there may be sparse glandular hairs on flower and leaf stalks. R. acridens is also similar, but its prickles are slender and more needle-like. Both are pricklier and even more uncommon than R. canadensis.