Gardnerian Wicca is the source of modern Wicca, and its own account of its origins is the part that has not survived examination.
Gerald Gardner, a retired colonial civil servant, published Witchcraft Today in 1954, three years after the repeal of the Witchcraft Act made it safe to do so. He described a surviving pagan religion, and said he had been initiated into a coven in the New Forest in 1939. His coven at Bricket Wood in Hertfordshire, working from 1954, is where the tradition begins as a documented thing.
The claim of ancient survival rested on Margaret Murray's thesis that the people tried for witchcraft in early modern Europe had been practitioners of a pre-Christian fertility religion. Historians have rejected that thesis. The trials were a persecution built on a fantasy, and the figure of nine million dead sometimes quoted for them is false by any serious estimate. Ronald Hutton, whose Triumph of the Moon is the standard history, concluded that a New Forest group is plausible but unproven, and that no such group could have been a survival of ancient paganism. Others have gone further and treated the coven as Gardner's invention, supplying the pedigree a new religion needed; Philip Heselton has argued the other way and named probable members.
The distinction that matters is this. Initiatory descent from Gardner is documentable, and Gardnerians trace it with care. Descent through Gardner to antiquity is not, and the tradition's better teachers stopped claiming it decades ago.