Identification of Rubus ursinus vs Rubus armeniacus

 A note before I begin: Rubus taxonomy is a mess right now. The native Californian species are pretty well defined, but the European / Asian originating ones (often called "Himalayan Blackberry") don't really fit neatly into our current taxonomic concepts. You will see many different names applied to non-native Rubus on the West Coast, and it's unclear if they should all be considered the same species or several different species, and what features should distinguish them from each other if they are different.

Various sources you will run across may refer to these plants as Himalayan Blackberry (Rubus bifrons), Armenian Blackberry (Rubus armeniacus), European Bramble Complex, Rubus discolor, Rubus fruticosus, Rubus vestitus, and probably a dozen other names as well. The Japson Manual calls these plants R armeniacus, so for the purposes of this guide, that is how I will refer to them.

So the most obvious difference between R armeniacus and R ursinus is the shape of the spines on the stem. For best results, look at the spines on the older parts of the plant; they're more likely to be fully developed.

Rubus ursinus / photo by jimkingdon

Rubus armeniacus / photo by kdeblonk

R armeniacus has more-or-less triangular spines (much broader at the base than at the tips) which are large, widely spaced, and fairly uniform in size compared to the other spines on the same stem.

R ursinus has narrow, needle-like spines, which don't vary much in width from base to tip. They're also usually densely packed together, and can vary a lot in length along a single section of stem.

Notice also the shape of the stems - Rubus armeniacus has ridges running along the stem, and in cross-section will look somewhat hexagonal. R ursinus has no ridges, and will appear round in cross-section. 

Younger and smaller specimens of R armeniacus will not always show the ridges as well as large, older canes, but will usually have at least some flattening of the sides of the stems.

Here's a few compilations of the thorns to give an idea of the variations:

Rubus ursinus thorns

Rubus armeniacus thorns

Another characteristic is leaf shapes. Mature leaves of R armeniacus usually have 5 leaflets arranged palmately, and mature leaves of R ursinus usually have 3 leaflets. On the rare occasions that R ursinus has 5 leaflets they will be arranged pinnately (more on that below).

This photo shows the "classic" mature leaf form of both species:

Notice how the R armenicus leaf has 5 leaflets originating at the same spot? This is known as "palmate" leaf structure. When R ursinus has 5 leaflets, they are pinnate in structure, with the top 3 originating at the same spot, and a another pair originating further down on the leaf stem:

Pinnate R ursinus leaf

When the leaves are on an immature plant or new growth, the leaflets are often fewer, or fused together - always try to find mature leaves just to be sure.

Here is an example of an R armeniacus seedling with only 3 leaflets, but the thorns are a good cue: 

And some of the younger leaves on this R ursinus are fused into a single leaf:

Finally, let's talk about flowers and fruit clusters.

R armeniacus has large clusters of around 10 to 20 flowers, located at the ends of the canes or branches. The flowers are 5-petaled, with wide rounded petals, colored white to pink. 

R ursinus has clusters with usually 1 to 5 flowers, growing on small branches coming off the sides of the main canes. The flowers are usually white, with narrow petals, and generally have 5 petals though it is not uncommon to have anywhere from 3 to 20+ petals on a given flower. 

On left: R ursinus flowers and fruit. On right: R armeniacus

Now that you've got those differences down, a final note..... yes, they do hybridize.

The hybrids look pretty much like you'd expect - somewhere in between the two. The thorns are dense, varied in size, but have thicker bases than you'd expect from R ursinus, and the canes are larger and more robust as well: