Well, I just explored into a cavern that was totally devoid of any plantlife whatsoever, so I'm afraid I have to rule out "unlucky" for you
Although, newbie that I am, what *are* bloodthorns? Are they just useless shrubs? Trees that you can't make lumber out of?
Also, I managed to lose all my sweet pod seeds from embark due to a farming mishap, but traded for them from the next dwarven caravan. You say your main civ doesn't have them? Is that even possible? I wonder if setting Plump Helmet Spawn to maximum priority next time the liaison meets with you will cause them to import some from somewhere else, since they know they have a prospective buyer who'll pay top dollar...
Hi.
Bloodthorns are subterranean trees, growing normally in the bottom cave layer. They're blood red, and so are items crafted out of them. Having only blood red beds, bins and barrels surely is sort of kinky.
I am reasonably sure that your dwarven civilization just grows plump helmets on the farming plots like everyone else, instead of hunting for mushrooms in the caverns. So, if you set the import priority of the plump helmets to maximum, you'll see a massive increase of these on the expense of other items. And that's it.
That's at least what happens if I set the priority of certain things to the maximum, and I don't see why it should be any different in regards as for plump helmets. Probably a bit less worse though than for instance with tree logs or rocks or metal bars, due to weight issues.