[Kameron8]

The Druid Devil Vines appear unable to grow into a tile that has a light shaft on it.

To replicate:

1.  Equip Druid, Brighten, Devil Vines, and Mass.
2.  Use Mass, then summon two Devil Vines.  Next, use Brighten on top of the two Devil Vines.
3.  Observe that the two plants grow, but cannot spread if no tiles are close enough without Light Shafts.

[Rendar]

The Druid Devil Vines appear unable to grow into a tile that has a light shaft on it.

To replicate:

1.  Equip Druid, Brighten, Devil Vines, and Mass.
2.  Use Mass, then summon two Devil Vines.  Next, use Brighten on top of the two Devil Vines.
3.  Observe that the two plants grow, but cannot spread if no tiles are close enough without Light Shafts.

They're unable to grow into any tile that has an already existing effect on it.

Ice, Cinders, Smoke Screen, Sanctuary (obviously), Dark Stage, Other Plants, Vines (Forma de Reduction Evade), Tall Grass (Forma De Evade Buff), dark water, acid tiles, etc etc...

Using Mass Brighten on Devil Vines actively cucks them 9 times out of 10.