Rubus armeniacus, the Himalayan blackberry[2] or Armenian blackberry, is a species of Rubus in the blackberry group Rubus subgenus Rubus series Discolores (P.J. Müll.) Focke. It is native to Armenia and northern Iran, and widely naturalised elsewhere. Both its scientific name and origin have been the subject of much confusion, with much of the literature referring to it as either Rubus procerus or Rubus discolor, and often mistakenly citing its origin as western European.[3][4][5]Flora of North America, published in 2014, considers the taxonomy unsettled, and tentatively uses the older name Rubus bifrons.[6]
In some areas, the plant is cultivated for its berries, but in many areas it is considered a noxious weed and an invasive species.
Description
Rubus armeniacus is a perennial plant that bears biennial stems ("canes") from the perennial root system. In its first year a new stem grows vigorously to its full length of 4–10 m, trailing along the ground or arching up to 4 m high. The stem is stout, up to 2–3 cm diameter at the base, and green; it is polygonal (usually hexagonal) in cross-section, with fearsome thorns up to 1.5 cm long forming along the ribs. The canes can turn more red/purple if they are exposed to bright sunlight. This is common in the summer. The leaves on first-year shoots are 7–20 cm long, palmately compound with either three or more commonly five leaflets. The leaflets are moderately serrated. Flowers are not produced on first-year shoots. In its second year, the stem does not grow longer, but produces several side shoots, which bear smaller leaves with three leaflets (rarely a single leaflet). These leaflets are oval-acute, dark green above and pale to whitish below, with a toothed margin, and snaring, hooked thorns along the midrib on the underside. The flowers are produced in late spring and early summer on panicles of 3–20 together on the tips of the second-year side shoots, each flower 2–2.5 cm diameter with five white or pale pink petals. The flowers are bisexual (perfect) containing both male and female reproductive structures.[7]
The fruit in botanical terminology is not a berry, but an aggregate fruit of numerous drupelets, 1.2–2 cm diameter, ripening black or dark purple. Both first- and second-year shoots are spiny, with short, stout, curved, sharp spines. Mature plants form a tangle of dense arching stems, the branches rooting from the node tip when they reach the ground.[8]
The fleshy growing cane tips contain the antifeedant compounds, 2-heptanol and methyl salicylate at higher concentrations than mature leaves. At the concentration found in the growing cane tips, 2-heptanol is a banana slug (Ariolimax columbianus) antifeedant. The lack of phytophagous insects observed on the growing cane tips is likely due to the presence of methyl salicylate. This compound is a known aphid repellant and has been shown to attract predators in response to insect herbivory.[9]
Cultivation
Berry crop
An example of the drupes, showing both unripe (green then red) and two ripe drupes.
The species was introduced to Europe in 1835 and to Australia and North America in 1885. It was valued for its fruit, similar to that of common blackberries (Rubus fruticosus and allies) but larger and sweeter, making it a more attractive species for both domestic and commercial fruit production. The immature fruits are smaller, red, and hard with a much more sour taste. The cultivarsHimalayan Giant and Theodore Reimers are commonly planted.[3][4]Rubus armeniacus was used in the cultivation of the Marionberry cultivar of blackberry.[10]
Cover
When established for several years, if left alone Rubus armeniacus can grow into a large cluster of canes. These thickets can provide good nesting grounds for birds, and help to provide places to rest/hide for other slightly larger mammals, such as rabbits, squirrels, and beavers.[11] While areas with R.armeniacus provide good sources for bird nests, birds do prefer areas with more natural/native plants when given the option.[12]
As an invasive species
Spread
Rubus armeniacus was first introduced to North America in 1885 by Luther Burbank in Santa Rosa, California, using seeds that he imported from India.[13][14] The species thrived in its new environment, notably for the large amount of berries it produced and was soon grown and cultivated in the United States by 1915.[15] It soon escaped from cultivation, and became an invasive species in most of the temperate world and the United States Pacific Coast by 1945.[16][3][4][17][10][18] Because it is so hard to contain, it quickly gets out of control, with birds and other animals eating the fruit and then spreading the seeds.[19] It is highly flammable and a common ladder fuel for wildfires,[20] due to the litter and dead canes produced by the plant.[21][22]
R. armeniacus bush covering a field in Germany
It is especially established west of the Cascades in the American Pacific Northwest[11] and in parts of southern British Columbia along the coast, in the Lower Mainland, and throughout Vancouver Island.[23] It does well in riparian zones due to the abundance of other species in these areas, which allows it to go relatively unnoticed until it has had a chance to establish itself.[10] Unlike other invasive species, this plant can easily establish itself and continue to spread in ecosystems that have not experienced a disturbance.[11]
The plant itself develops large root systems, allowing it to find water from other sources than just the immediate area. It can also hold onto water in its canes, allowing it to thrive more than other plants during dry seasons or droughts.[24] Himalayan blackberries grow very well in sandy, well-drained soil with a lot of natural light, even if the soil is lacking in nutrients.[25] All of the Himalayan blackberry's adaptations to grow in these conditions continue to make it a difficult plant to remove and an invasive species. R.armeniacus is able to survive during drought periods because of their extensive root systems. Not only are their roots spread out over a wide area, they also can go very deep underground, allowing them to reach water most smaller plants and shrubs would not reach.[25] They also store more water in their canes that act like a water reservoir.[24] This added water also allows them to release oxygen and take in more CO2 without fearing major losses of water. Since they store water in their canes and roots, they have excess water ready for use or for loss when opening their stomata.[24]
Management
Cutting the canes to the ground, or burning thickets of Rubus armeniacus are ineffective removal strategies. The best practices for removal include digging up the rhizomes and connecting underground structures, and herbicides.[10] Broken roots can resprout, making manual removal extra labor-intensive, and glyphosate herbicides are largely ineffective with this plant.
^USDA, NRCS (n.d.). "Rubus armeniacus". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 24 October 2015.
^ abcCeska, A. (1999). Rubus armeniacus – a correct name for Himalayan Blackberries Botanical Electronic News 230. Available online.
^Flora of North America editorial committee (2005). Flora of North America: North of Mexico. Oxford University Press. ISBN9780195222111. OCLC469452032.
^Francis, J.K. (2003). Rubus discolor Weihe & Nees. pdf file
^Wood, William F. (2012). "Banana slug antifeedant in the growing cane tips of Himalayan Berry Rubus armeniacus". Biochemical Systematics and Ecology. 41: 126–129. doi:10.1016/j.bse.2011.12.029.
^National list of naturalised invasive and potentially invasive garden plants (Australia) pdf file
^Bennett, Max (August 2006). "Managing Himalayan blackberry in western Oregon riparian areas". OSU Extension Catalog. Oregon State University Extension Service. hdl:1957/20389. S2CID128858520. PDF. Retrieved 2022-07-04. It escaped cultivation and has since invaded a variety of sites, including low-elevation streamside areas throughout the Pacific Northwest. Listed as a noxious weed in Oregon, Himalayan blackberry rapidly occupies disturbed areas, is very difficult to eradicate once established, and tends to out-compete native vegetation. For those trying to restore or enhance native streamside vegetation, Himalayan blackberry control is a major problem.
