Rubus ferrofluvius (Iron River Dewberry)
|Also known as:
|part shade, sun; average to dry sandy or peaty soil; savanna, forest clearings,
|May - June
|6 to 12 inches
|Wetland Indicator Status:
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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A compact, flattish/convex cluster (corymb) at the tips of short lateral shoots along 1-year-old stems, each cluster with 2 to 8 flowers. Flowers are white, about 1¼ inch (2.5 to 3.5 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, triangular to elliptic, pointed or with a short tail-like extension at the tip, the outer surface sparsely to moderately covered in non-glandular hairs. Flower stalks are similarly hairy and may have a few 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 usually have a single lobe on the lower half. Leaflets are sharply toothed around the edges, sparsely hairy on the upper surface, usually moderately hairy on the lower but can vary from sparse to velvety. The terminal leaflet on primocanes is 2¾ to 3½ inches (7 to 9 cm) long, up to about 2 inches (4 to 6 cm) wide, widest near or below the middle, rounded to wedge-shaped at the base, tapering to a short or long extension at the tip.
Leaflet stalks are sparsely covered in non-glandular hairs and scattered curved prickles. At the base of the compound leaf stalk is a pair of appendages (stipules), lance-shaped to linear, up to ¾ inch (10 to 20 mm) long.
Prickles are up to 1/8 inch (1 to 3 mm) long, slender and needle-like to slightly broad-based, straight to curved, and sparsely to moderately abundant. Stems are green to dark red, hairless, up to 8 feet (to 2.4 m) long but low-growing, trailing along the ground and rooting at the tips, and die the second year after fruit matures. Colonies may also form from root suckers.
Iron River Dewberry is an uncommon species in Minnesota, where it reaches the northwest edge of its range. It's been recorded in savanna type habitats, brushy or grassy openings in Jack pine and mixed woodlands, in the transition zone between wet meadow and upland prairie, and in rock outcrops in the Boundary Waters Canoe Area. The preference is dry, sandy soil, full sun to part shade.
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.
In many references Rubus ferrofluvius is lumped in with Rubus flagellaris, along with other MN species R. ithacanus, R. multifer, R. plicatifolius, R. satis, and R. steelei, 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. flagellaris is apparently a dumping ground for Dewberries that have broad-based prickles and stems that trail along the ground, rooting at the tips, but other characteristics can be rather variable.
Rubus ferrofluvius is identified by the combination of: lacking any glandular hairs; prickles sparse to moderately abundant, slender and needle-like or more often slightly broad-based, mostly curved; leaves all have 3 leaflets, the lateral leaflets usually lobed, lower surface is usually moderately hairy but can vary from sparse to velvety; flowers are in a compact corymb with 2 to 8 flowers, sepals and stalks are sparsely to moderately covered in non-glandular hairs. Canes can reach 8 feet long, trail along the ground and root at the tips.
The consistent 3 leaflets, slightly broad-based prickles, and trailing stems that root at the tips are the stand-out characteristics of R. ferrofluvius. R. steelei is most similar, also having trailing stems that root at the tips, usually has 3 leaflets but occasionally 5, and prickles are more distinctly broad-based. R. uniformis is the only other MN species that consistently has 3 leaflets, but its prickles are all slender and needle-like, usually more abundant, and its stems are low-growing but do not trail along the ground or root at the tips.
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- primocane in mid July
- flowering in mid June
- a loose colony
- stem trailing along the ground
- stem rooting at the tip in mid August
- stipules are lance-linear
- lower surface leaf hairs are usually moderately dense but variable from sparse to velvety
- a 2-flowered cluster
- flowers are ~1¼ inches (2.5 to 3.5 cm) diameter
Photos by K. Chayka and Peter M. Dziuk taken in Pine County.
Have you seen this plant in Minnesota, or have any other comments about it?