I mentioned Collective Farm Woman honeydew a few weeks ago. The seed company slipped my mind - in fact it was The Lost Seed, who are a good bunch, although I do like taking the mickey.
We have a packet of their Bloomsdale Longstanding spinach seeds. The spiel on the packet warns helpfully that it will "cross easily with other spinach varieties; to ensure purity, grow varieties at least 3km apart."
So that explains those spinach-eradication ninjas who I have seen creeping about the suburbs at night. Just maintaining the "purity" of their precious Bloomsdale Longstanding spinaches.