Flower:

Raceme or somewhat flattish/convex cluster (corymb) at the tips of short lateral shoots along 1-year-old stems, each cluster with 5 to 19(35) flowers. Flowers are white, about 1 inch (2 to 3 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, triangular to egg-shaped, mostly with an elongated tip, the outer surface covered in short non-glandular hairs mixed with sparse, longer glandular hairs. Flower stalks are similarly hairy, sometimes with a few slender prickles. At the base of a flower stalk is a leaf-like bract, typically resembling the largest stipules (see leaf description below).

Leaves and stems:

Leaves are alternate and palmately compound, non-flowering first-year stems (primocanes) with mostly 5 leaflets, sometimes 3 on the lower stem, and flowering second-year stems (floricanes) with mostly 3 leaflets. Leaflets are coarsely toothed or double-toothed around the edges, mostly hairless on the upper surface, hairless or sparsely hairy along major veins on the lower. The terminal leaflet on primocanes is 2½ to 4+ inches (6 to 11 cm) long, up to 2¾ inches (4 to 7 cm) wide, elliptic to somewhat diamond-shaped, mostly widest near the middle, rounded to tapering at the base, abruptly tapering to a short extended tip.

Leaflet stalks are hairless to sparsely hairy, occasionally with a slender prickle or two. At the base of the compound leaf stalk is a pair of appendages (stipules), the largest at least ¾ inch (2 to 3.5 cm) long, those on the lower stem typically broad and often notched along one side, those on the upper stem often lance-linear and not notched.

 Prickles are up to 1/8 inch (1 to 3 mm) long, slender and needle-like, straight or declined, and often weak and sparse. Stems are green to reddish, hairless, up to 5 feet (to 1.5 m) long but low-growing, low-arching to nearly prostrate, but not trailing along the ground or rooting at the tips; stems die the second year after fruit matures. Loose colonies may form from root suckers.

Fruit:

Fruit is a round cluster of fleshy drupelets, up to about ½ inch (8 to 14 mm) diameter, maturing from green to red to black, and are quite tasty.

Notes:

Big Horseshoe Lake Bristleberry has a very limited geographical range with the largest populations in Minnesota, where it is still rare. According to the DNR, it's primarily found in what was once oak savanna with a mix of prairie and groundwater sustained wetlands, mostly within the Anoka Sandplain. Much of that historical habitat has been degraded or destroyed by converting land to agriculture or suburban development, as well as the encroachment of invasive species. It was listed as an Endangered species in 2013. As of this writing, there are fewer than 20 herbarium records but in recent years several new populations have been discovered within the Twin Cities metro area and one even as far north as Itasca County.

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 stipulatus is identified by the combination of: glandular hairs present only in the flower/fruit clusters, not leaves or canes; prickles usually sparse, weak, slender and needle-like, straight or declined; primocane leaves with mostly 5 leaflets, sometimes 3 on the lower stem, lower leaf surface hairless except for sparse hairs on veins; flowers in a raceme or flattish/convex cluster (corymb), 5 to 19+ flowers per cluster; sepals and stalks short-hairy mixed with longer glandular hairs. Canes can reach 5 feet long but are low-arching to nearly prostrate, not known to root at the tips. The epithet stipulatus comes from the large, distinctive stipules, the largest often over 1 inch long, broad and typically notched along one side; these are best seen on the lower half of primocanes. The upper stipules may be just as long but more linear. Floral bracts resemble the largest stipules, giving the cluster a leafy appearance.

In some references Rubus stipulatus is lumped in with Rubus setosus, along with about 10 other MN species, but we follow the treatments by Mark Widrlechner and documented by Welby Smith in his book “Trees and Shrubs of Minnesota”, which keeps them split as separate species. R. setosus is essentially a dumping ground for species with needle-like prickles: primocanes with 3 or 5 leaflets, leaves velvety or not, with or without glandular hairs, flowers in a raceme or corymb, stems root at the tips or not. In some other references R. stipulatus may be lumped in with R. dissensus, which has more abundant glandular hairs on floricanes, usually some also on primocanes, and is moderately to abundantly prickly.