Plants are large, specialized beasts that act as factory bio-structures from which low rank beasts are mass-produced in huge volumes. It has the ability to erode and produce beasts independently by themselves. As such, they are fielded in the front lines to serve as surrogates both to their Queen's womb and the Nest.
Plants develop from special seeds that are launched directly to battle fields where they eventually grow and serve their purpose. Its production is limited to certain breeds and types only - usually low rank beasts and bio-materials that mimic human technology such as warships and weaponry. Only the artificial womb in Nests or from the personal womb of the Queen herself can produce high rank beasts up to the EX-Types.