Elmleaf blackberry (Rubus ulmifolius, Schott 1818)

Identity

Elmleaf blackberry (Rubus ulmifolius Schott, 1818) scrambles through hedgerows from France to the Mediterranean region, growing on chalky as well as clay soils. This shrub belongs to the Rosaceae family. Its epithet ulmifolius describes toothed leaflets that resemble elm leaves; it does not imply any botanical relationship with elm trees. ^{1 5}

An unusual genetic feature separates it from its relatives: Rubus ulmifolius uses normal sexual reproduction, whereas almost all other species in subgenus Rubus clone themselves through apomixis. That process preserves hundreds of nearly identical microspecies across Europe. ⁴

Recognition

Angular, arching or trailing canes often show a reddish tint and carry strong, curved prickles. Elmleaf blackberry reaches 1–5 m (3–16 ft) tall and 2–4 m (6.5–13 ft) across. The size of a thicket depends particularly on its age and the supports available for the stems to climb through. ³

Each leaf has 3–5 toothed leaflets, dark green and glossy above but covered underneath with a distinct white woolly layer. These pale undersides contrast with the green undersides of many brambles in the fruticosus complex. Turning over a leaf is therefore a useful first field check, even before counting the leaflets. ⁴

Loose flower clusters appear at the tops of second-year canes. Flowers have five pink or white petals and measure about 2–3 cm (0.8–1.2 in) across. Their aggregate fruits turn from green to red and finally glossy black when fully ripe. The individual drupelets are more tightly packed and less juicy than those of some cultivated blackberries. ^{7 3}

Useful taxonomy

Within the notoriously complex genus Rubus, the established name is Rubus ulmifolius Schott, 1818. Other names have been applied to this species or closely related forms: Rubus rusticanus Mercier, Rubus caldesianus Focke, Rubus cruentiflorus Sudre and, more recently, Rubus maroccensis Huan C.Wang & H.Sun.

The Moroccan case illustrates the difficulty of delimiting brambles. Described as a new species in 2013, that population was subsequently placed in the synonymy of the much earlier-described Rubus ulmifolius. Plants of the World Online currently treats Rubus ulmifolius as the accepted name. ^{1 2}

Habitat and distribution

Northwestern and central Europe connect with the western and central Mediterranean in the native range recorded by WCVP, extending into northwestern Africa. In France, Elmleaf blackberry is considered native across most of the country, without a recognized invasive status there. ^{1 5 6}

Introduced populations have caused documented ecological problems. In Australia, Rubus ulmifolius belongs to the Rubus fruticosus complex, treated as a priority invasive alien weed. That complex infests about 9 million hectares (22 million acres) and forms impenetrable thickets. ⁷

On Robinson Crusoe Island in Chile's Juan Fernández archipelago, Rubus ulmifolius arrived in 1927. It now covers approximately 7% of the island, which supports a flora with an exceptionally high proportion of endemic plants. ⁹

Life cycle and reproduction

Pollination and fertilization in Elmleaf blackberry follow the usual sexual process. This contrasts with almost all other brambles in subgenus Rubus, whose seeds can produce copies of the mother plant through apomixis. The difference makes this species useful for studying how apomixis became widespread elsewhere in the genus. ⁴

Individual canes live for only two years. A cane grows without flowering during its first year, then branches, flowers and fruits in its second year before dying. When a cane tip touches the soil, it roots spontaneously. A single plant can consequently spread across several square meters without human intervention. ³

Fruit-eating birds, particularly blackbirds and thrushes, provide much of the longer-distance seed dispersal. They swallow the blackberries and later pass the seeds intact, often far from the parent plant. Local tip-rooting and distant bird dispersal together explain the rapid colonization seen where the species has been introduced. ⁹

Uses and risks

Ripe blackberries are the main documented food use, eaten raw or prepared as jam or syrup like the fruits of other Rubus brambles. No toxicity is documented for the fruit or foliage. During picking, the practical hazard comes from the strong stem prickles, which readily scratch exposed skin. ³

Ecological damage is a more significant concern where the species has been introduced beyond Europe without its natural predators and diseases. Dense Rubus ulmifolius thickets exclude native vegetation, alter fire regimes and restrict access to affected land. ⁷

Australian control programs sometimes use pathogenic fungi such as Phragmidium violaceum, a rust fungus affecting raspberries and brambles, as biological control agents. On Rubus ulmifolius, this disease weakens the foliage without eliminating the plant itself. ⁷

Varieties and similar plants

Hundreds of closely related microspecies make up the broad Rubus fruticosus complex to which Elmleaf blackberry belongs. Distinguishing every one with confidence usually requires a bramble specialist, known as a batologist. Gardeners and walkers can begin with the woolly white leaf undersides, which already rule out many green-backed brambles. ⁴

Three nearby relatives cause frequent confusion. Rubus fruticosus, used broadly for the complex, often has less woolly leaf undersides. European dewberry, Rubus caesius, has relatively few prickles and fruit covered by a characteristic bluish bloom. Red raspberry, Rubus idaeus, leaves its receptacle behind when picked, whereas an Elmleaf blackberry retains the receptacle inside the harvested fruit.

The genus name Rubus alone cannot identify an individual bramble. Looking closely at the underside of a leaflet, whether white and woolly or smooth and green, remains an accessible way to separate Elmleaf blackberry from many of its relatives.

Main sources

• Plants of the World Online / Kew, Rubus ulmifolius Schott
• International Plant Names Index, Rubus ulmifolius
• Plants For A Future, Rubus ulmifolius
• Wikipedia EN, Rubus ulmifolius (elmleaf blackberry)
• Tela Botanica / BDTFX reference database, Rubus ulmifolius
• INPN / MNHN, Rubus ulmifolius Schott, 1818
• Weeds Australia, European blackberry (Rubus fruticosus aggregate)
• InfoFlora Switzerland, Rubus ulmifolius
• PMC / NCBI, Human Impacts on the Vegetation of the Juan Fernández (Robinson Crusoe) Archipelago