Linking the spread to another trait is useless as long as the required value exists in some other plant's gene. E.g. it's quite easy to make potency 50 spreading plants.
As master botanist, the current code "outside a tray" mode annoys me because the spread gene is an easy way of growing strange plants in quantity for chemistry, but there's definitely no need to grow so many.
The behaviour is also wrong in the sense that it acts like the kudzu gene, with the only exception that the kudzu gene changes the appearance of the plants and can block sight.
I have to say also that botanics is quite cramped, and xenobotany should be in its own airlock space. The other day I had, but didn't release, a nitrogen producing "outside a tray" plant that would have ended the station. Still not as dramatic as what Virology, Xenobiology, Atmos and Engineering can do, but Botanics is missing the "things will be ok as long as the stuff is contained" -- because there's no proper contained area for hypercrops.
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