Rubus argutus aka Saw Tooth Blackberry

Rubus argutus belongs to the rose family. Its common name is highbush blackberry. It is native to the central and eastern United States. It grows in temperate regions, but not as a native in Britain or Ireland. Sources differ on how to group this species with other blackberries. Useful Tropical Plants says USDA treats it as a distinct species. The same source reports a different view from Flora of North America. That work groups it with Rubus pensilvanicus.

This shrub sheds its leaves and has a woody rootstock. Its canes stand upright or arch, and form thick patches. The listed height is about 8 feet [2.5 metres]. Cane lengths range from about 3–10 feet [1–3 metres]. Virginia Tech says these patches can grow above head height. Each cane lives for two years, but the rootstock lives on. First-year canes bear leaves but do not bloom. In year two, they grow branches that bear flowers. Those canes die once they have borne fruit.

The thick canes have clear angles. They bear large prickles with a slight curve. Their surface is dull red-brown, with no waxy coat. Bark grows darker with age, and cane tips do not root. Leaves grow in turn on each side of the stems. Each leaf has three to five leaflets, most often three. These leaflets can be lance-shaped or oval. Their edges have teeth. The upper sides shine green, and the lower sides look paler. The leaf stalks also bear prickles.

White flowers grow in groups at the ends of stems. Each bloom measures about one inch across. Blooms appear from late spring into early summer. Insects carry pollen to the flowers. Many small drupes, or fruit units, join to form the juicy fruit. It turns black and measures about half an inch long. The core stays inside the fruit when people pick it. Fruit ripens in June and July. People gather this plant for food and medicine. Growers also raise it for fruit in North America. It has helped produce several forms of blackberry grown in gardens.

In its native range, it can help hold soil. It also plays a part in restoring native woodland. Beyond that range, its spread can cause serious problems. It competes with native plants. It spreads by seeds and by growth of plant parts. Disturbed soil and gaps in the tree canopy help it spread. Deep shade limits growth. Roots already in place can send up shoots after cutting or spraying. New Zealand and Japan have declared it a noxious weed. Hawaii also lists it as a major weed that harms the environment.