Rubus spectabilis Pursh, Salmonberry

Account Summary

Growth form and introduction

A deciduous perennial shrub with an extensive branching rhizome and annual canes up to 4 m tall, native of western N America, R. spectabilis was introduced to B & I in 1827 by the famous Scottish plant hunter David Douglas. It was quickly taken up for its decorative flowers, for breeding of autumn-fruiting and disease-resistant raspberries, as an almost prickle-free cane-forming shrub for game cover in estate woodlands and to stabilize steep banks along roads and streams (Roach 1985; Oleskevich et al. 1996; Mitchell & House 1999). R. spectabilis avoids cold temperatures and is restricted to mild, maritime climates. It has a relatively high shade tolerance and shows a strong preference for open, moderately disturbed, moist, water-receiving sites with well-aerated soils, of which it is a vigorous pioneer colonist. In a mild winter, with mean temperature of 6°C or above, R. spectabilis can continue minimum shoot extension throughout (Oleskevich et al. 1996).

It is not known exactly when it escaped from cultivation into the wild, but it had certainly done so and become thoroughly naturalized by the end of the 19th century in many areas of B & I and it now appears to be increasing (D.J. McCosh, in: Preston et al. 2002).

Flowering reproduction

This very vigorous, tall, deciduous, thicket-forming shrub declares its presence early in the spring, producing solitary, conspicuous, 20-30 mm diameter, bright purple flowers on short, leafy lateral shoots on mature canes from the middle of March through into June, followed by large, orange, edible fruits (Sell & Murrell 2014). The flowers are self-sterile and cross-pollination by insect visitors is obligatory. While the fruit looks like a large unripe raspberry (bright red, orange or yellow in colour), it is disappointingly rather tasteless. Thrushes do not seem to mind, however, and they consume them and may spread the seed over considerable distances. Seed can survive burial in soil for at least 100 years, making the species very persistent and extremely difficult to eradicate (Oleskevich et al. 1996).

Vegetative reproduction

Once established in a site, the plant consolidates itself by suckering vigorously from its spreading underground rhizome, rapidly forming dense, multi-layered, clonal stands. These can outgrow and effectively exclude local competitors, eventually establishing dense single-species stands (Oleskevich et al. 1996).

Northern Ireland occurrence

Salmonberry is actively spreading throughout NI and the hectad map in the New Atlas shows that Ulster (ie the nine-county northern portion of Ireland) has the greatest continuous hectad distribution of the species anywhere in B & I (Preston et al. 2002). R. spectabilis was first observed in the wild in E Donegal (H35), Tyrone (H36) and Down (H38) in 1931, Londonderry (H40) around 1945, Antrim (H39) in 1956, Fermanagh (H33) in 1976 and Armagh (H37) in 1981 (FNEI 3; Cat Alien Pl Ir).

Fermanagh occurrence

R. spectabilis is now known in Fermanagh from 29 tetrads, 5.5% of those in the VC, but inexplicably it is confined to the N & W of the county. It occupies disturbed ground along linear landscape features (often the first ground to be colonised by alien species) in moist, semi-shaded conditions in a wide variety of soils along river and stream banks, lakeshores, hedgerows and roadsides. The shrub is very persistent in gardens around long-derelict properties where it was obviously planted.

Irish Republic and British occurrence

R. spectabilis appears to be rather scarce and widely scattered in the RoI, although Reynolds (2002) does catalogue its presence in ten VCs there. Many of the sites listed in the RoI are from roadside hedges, in estates or near gardens or churchyards where it has been planted, although some are clearly 'escapes' or garden discards in damp lakeshore or riverside woods and in thickets. In Britain, it is likewise very thinly but widely spread, except in the Scottish Midlands where it is concentrated around the two major cities and their hinterlands. In some Scottish sites, the species has persisted more than a century (Clement & Foster 1994; Preston et al. 2002).

Threats

Naturalised, actively spreading, persistent, potentially invasive alien that requires monitoring.

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