Lord Blade wrote
On my fifth time fully exploring the level, I found the boss plant. The other times, I'd explored everything I could get to, and couldn't find that plant room. Guess it was just bad luck with level design. Wouldn't be the first time I found a room that wasn't attached to the rest of the level.
I've been playing IVAN for years, and I've not seen or heard of a single time Genetrix hasn't spawned.