Cherrypicked xenophage-rewrite mechanics over.

code/game/objects/structures/alien/node.dm

@@ -0,0 +1,19 @@
+/obj/structure/alien/node
+	name = "alien weed node"
+	desc = "Some kind of strange, pulsating structure."
+	icon_state = "weednode"
+	health = 100
+	layer = 3.1
+
+/obj/structure/alien/node/New()
+	..()
+	processing_objects |= src
+
+/obj/structure/alien/node/Destroy()
+	processing_objects -= src
+	..()
+
+/obj/structure/alien/node/process()
+	if(locate(/obj/effect/plant) in loc)
+		return
+	new /obj/effect/plant(get_turf(src), plant_controller.seeds["xenomorph"])