Whenever the celestial or fiendish planes intersect with the material one, there is an opportunity for a commingling of flora.
Celestial Varieties
Heavenly flora is often found growing near sacred sites associated with good-aligned gods. Temples, shrines, tombs, and worshipping places are all excellent spots for these plants to take hold. They also form near rifts between the Material Plane and a celestial one; the course of their growth can be tracked to locate the portal.
Slow Growing. Celestial flora take a long time to grow into mature plants. They often require protection from animals or curious humanoids in their early stages of development. Druids, clerics, paladins, and priests of good-aligned gods often act as keepers and guardians of these plants. These holy tenders are empowered by the plants and are often rewarded by their patron deity for their work. The plants might also sprout up miraculously at the site of a powerful celestial’s arrival on the Material Plane. If the being is of sufficient power, an entire lustrating grove may erupt into being rapidly.
Cleansing. Celestial plants have a natural ability to cleanse cursed and soiled ground. They can be cultivated in an area corrupted by demonic or infernal magic and, given enough time, eradicate the evil. The process is long, but, if the plants are properly tended, the outcome is guaranteed.
Sustained by Miracles. Celestial plants do not require water or sunlight to grow. They flourish anywhere their roots can find purchase, including underground caverns, shadowy mountain valleys, and harsh deserts.
Lustrating Groves. Left alone, a single celestial plant eventually grows into a large grove. The groves are places of intense radiant magic that call to divine magic wielders for miles around. These holy places contain great power and commune spells resolve with greater clarity and success. The groves are often guarded by angels or other celestial beings who see the site as a foothold on the Material Plane.
Fiendish Varieties
Fiendish flora grows at sites where great evil has transpired, where foul things are worshipped, and where devils and demons have tread. These foul life forms are carnivorous and require blood to grow and thrive on the Material Plane. Cunning devils cut and clip the plants into unholy gardens which bolster their powers. Demons promote the flora’s wild and expanding nature, sacrificing animals and humanoids to allow the fiendish plants to grow as rapidly as possible.
Carnivores. Fiendish plants require blood to grow. On the Material Plane, the plants do best in forests where careless animals are plentiful. These evil, sentient plants form relationships with all manner of dark-hearted beings. Fiendish flora offer power and protection in exchange for fresh blood. The craven nature of these plants often sees them devouring their allies when fresh blood is scarce.
Discord, Dismay, and Darkness. The fiendish plants propagate and thrive wherever there is a concentration of evil, chaos, and misery. If a fiend treads the Material Plane, there is a good chance that fiendish plants will trace its steps. A single shrub hidden in a farmer’s field can affect the temperament of nearby animals and humanoids, causing nightmares, depression, and a darkening of disposition.