Some biomes definitely like each other more than others. Ice biomes like forest biomes better than desert biomes. I think there are some biomes that need at least one other biome to merge, and if they don’t have one of those, they will add a little bit of an unselected biome to make the merge work.
I’m not going to pretend to understand how the entire algorithm works, but I’ve spawned a lot of planets and I’ve noticed some patterns in what they do. Ice and desert don’t seem to like each other very much. Some of the varying altitude biomes don’t like each other much, but this depends on whether they can cut holes in each other or not. Lantern field prefers to have a water body but will plant itself on any flat biome if it cannot find water. Olympus and cube field are BFFs. If you try and force the algorithm to do things it doesn’t want to do, sometimes it spites you.
my point of view, never though about it earlier but, if 2 large biomes normally counts as 2 regions merges into 1 aere counted as 1 region?
i saw at Centon ice/glacier biome merged with sand/tangle/thorns biome where ice took place of sand and we have tangle/thorns structure at ice, it might be possible that those 2 regions now are count as 1?
also - there were no river biomes chosen but there are decent amounnnnt of water, did water covered few regions and made it 1?
On SOV planet [Charoite] I found this giant purple basket tree today,
Nothing strange in itself …
… But on top of it, ready to start chopping my way down …
I discovered, that this one was joined by four others nearby, in the same biome
My new base would have been totally boring… but @Draconic made me some wonderous stairs! all the little details are fantastic… Dude rocks the building.
Ancient Bamboo on 
[DrummersDomain] …
didnt found them yet at your sov 
