The thing with members of the European Blackberry Complex is that they set seed apomicticly (without sex). Therefore, a population derived from seeds and covering a large area may be a single clone. It looks like a species because it’s growing alongside another clone that differs from it a little bit in several traits. That’s the kind of consistent, multitrait difference we’d like to treat as a species. And there’s a third clone. And a fourth. Etc. All a little different. Lots of “species.”
These all do have sex occasionally and produce seed from these unions. If the parents were different clones, these offspring are a little different from both – they are hybrids – and they can form a new clone that spread over a large area while retaining their traits, their differences from the other clones around. They seem to be behaving like distinct species.
As you can see, I’m not fond of treating all these different members of the European Blackberry complex as species. But there is a lot of variation in the group. Some of these variations help the clones adapt to different environmental conditions. Some differences look worth treating at the species level. But if you start dividing the group up, where do you stop splitting? This is a crazy-making situation for botanists.