Peduncle trees are only present in those two regions (Dryman's Point and Sagittarius-Carina Arm), although I've heard that they are in Hawking's Gap too, but bugged and can't be scanned there. Be that as it may, they are numerous there because their requirements aren't strict: their area covers the entire region, and their star / body requirements are quite permissive.
As far as I can tell, if all required conditions are met, then NSPs spawn 100% of the time. (So it's not a, say, 50% chance to spawn in correct systems.) However, the Codex doesn't always list all the actual requirements, and there's also the area requirement. (Not just within the region, but within a certain area of the region.)
Now, all Peduncle tree variants (discovered so far) have the following requirements:
- The system should contain at least one of the following star types: F, G, K, M
- The system should contain at least one of the following body types: ELW, WW, GGWL, CII GG, WG
- The system should not contain a Wolf-Rayet star (this is an universal requirement)
Similarly, the IOS is full of NSPs because Albulum Gourd Molluscs have quite permissive requirements too, and their area covers the whole sector. The only difference there is that they need a T star present (doesn't have to be the main star) instead of FGKM.
If either the Albulum gourd molluscs or any of the peduncle trees didn't have a region requirement, then the galaxy would be quite full of NSPs. And we'd miss the rare stuff, because people would quickly grow bored of them in general.
I have to say though, that's a pretty good screenshot!
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