From the White Wolf Wiki, the most complete White Wolf reference

The Gardeners of the Tree are one of four factions within the Verbena. They are Pattern mages who try to keep the old ways alive and pure, thus tending the base of the metaphorical tree which is the Verbena.

They keep records, track genealogy, and trace the heritage of Verbena rituals. Conservatives among them only count "true Verbena" as those who have a blood tie to one of the families at the root of the Tradition. More flexible members content themselves with remembering old rites and propagating the spread of the fundamental elements of their heritage.

[edit] Background Information

The name of the faction is an homage to Gerald Gardner, the founder of modern Wicca.