The elder is one of the few European trees with a well-attested guardian spirit and a protocol for dealing with her.
The Elder Mother, Danish Hyldemoer, and cognate figures in German and English tradition, is held to inhabit the tree, and the requirement is to ask leave before cutting it. The formula recorded in English and Scandinavian sources runs to the effect of: Old girl, give me some of thy wood, and I will give thee some of mine when I grow into a tree. Burning elder on the hearth was widely held to be dangerous or to bring the Devil down the chimney, and elder was nonetheless planted deliberately by houses and byres as a guard against witchcraft and lightning. A tree that both protects and must be placated is doing two jobs.
This creates a real tension with the planetary attribution. Culpeper puts elder under Venus, which reads it as a benign, healing, cooling plant, and that fits the flowers and the berries. Modern occult compilers frequently reassign it to Saturn instead, on the strength of the guardian spirit, the funerary associations, the taboo on burning, and the tree's habit of growing on graves and waste ground. That reassignment is not a correction of Culpeper by better evidence; it is a different tradition weighing a different set of facts and reaching a different answer.
Both attributions are therefore defensible on their own terms and neither is ancient. The honest description is that the source disagrees with the modern consensus, and that the disagreement is about which half of the tree's reputation counts.