Flower:

Small, often branching clusters at the tips of short lateral shoots along 1-year-old stems, each cluster with 2 to 6 flowers, sometimes with single flowers or smaller clusters arising from leafy nodes below it. Flowers are white, about 1 inch (2.5 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, oblong-elliptic to egg-shaped with an elongated tip, the outer surface thinly covered in non-glandular hairs. Flower stalks are similarly hairy and may have scattered, slender prickles.

Leaves and stems:

Leaves are alternate and palmately compound, both non-flowering first-year stems (primocanes) and flowering second-year stems (floricanes) with 3 leaflets; the lateral leaflets typically have a shallow lobe on the lower half. Leaflets are toothed or double-toothed around the edges, sparsely hairy on the upper surface, sparsely to moderately hairy on the lower, not velvety. The terminal leaflet on primocanes is up to 5½ inches (8 to 14 cm) long, up to about 4 inches (to 10 cm) wide, broadly egg-shaped, widest below the middle, rounded to somewhat heart-shaped at the base, pointed at the tip.

Leaflet stalks are sparsely covered in non-glandular hairs and scattered prickles. At the base of the compound leaf stalk is a pair of appendages (stipules), variable in shape, broadest below or near the middle, up to ½ inch (5 to 15 mm) long.

Prickles are up to 1/8 inch (2 to 3 mm) long, slender and needle-like to broad-based, straight to curved, ascending to declined, and sparsely to moderately abundant. Primocane stems are covered in a whitish bloom and are light green to bluish, or red-tinged where exposed to sun. Stems are branched, up to 6 feet (to 2 m) long, initially erect but arching over around knee height forming low mounds, the tips trailing and taking root where they touch the ground, and die the second year after fruit matures. Dense colonies can form from root suckers and tip-rooting.

Fruit:

Fruit is a cluster of 1 to several large (for a Rubus ), oval to round, fleshy drupelets resembling blueberries, blue-black with a waxy bloom when mature, though fruit production is generally poor.

Notes:

Rubus caesius is a recent discovery in Minnesota with only one known location at this time, in Hennepin County, though that doesn't mean it hasn't gone unnoticed elsewhere. It is said to have been introduced to North America from Russia in 1897, escaped cultivation, and was reported as naturalized around Ithaca, NY, by 1940. Wisconsin has recorded multiple large, dense populations, at least one of which is in the Mississippi River floodplain, and a recent report on iNaturalist shows it consuming a large plot of land west of Chicago. The sole population in Minnesota should be a candidate for “early detection, rapid response” that invasive species experts like to promote, but rarely achieve in practice. Hope we can nip this one in the bud.

Rubus caesius has a few unique characteristics that should distinguish it from our native species, especially when taken in combination. One is that it blooms from June through October, where the natives are all done blooming by mid July. Another is the fruit, which has much larger drupelets than raspberries or blackberries, more closely resembling the size and color of wild blueberries. It also has 3 leaflets on both primocanes and floricanes, which is not unique by itself but can be an indicator. While the canes can reach 6 feet long, they tend to arch over at knee to thigh height, forming a mounding tangle, then thread their way through the tangle until the tip reaches the ground, where it takes root to start a new plant. Note that the prickles may vary from straight and needle-like to curved and broad-based, so checking multiple stems is recommended.

In its native range spanning Europe and Asia, it it most ofen found in habitats with rocky soil and light shade, at forest edges, thickets, and creek and river banks. In the US, likely places are areas of disturbance such as roadsides, trail edges and floodplains, as well as open woods, forest edges, and grassy areas.