Holly, Ilex aquifolium, is a broadleaved evergreen whose glossy spined leaves and bright red winter berries made it a natural decoration for the dark of the year long before it was Christian. The Romans used holly in the midwinter festival of Saturnalia, sending boughs of it as gifts and hanging it in honour of Saturn. Its evergreen persistence through winter, when most trees are bare, is the plain observable fact behind its symbolism of life enduring through the dead season, the same logic that attaches to ivy, mistletoe and the other midwinter greens.
Holly wood has a genuine practical history distinct from its symbolic use as greenery: dense, fine-grained and among the whitest of European timbers when freshly cut, it was prized for chess pieces, inlay work and knife handles, sometimes dyed black to stand in for ebony in marquetry, a workaday craft tradition running alongside the tree's decorative and religious use at midwinter. Holly has a caffeinated relative most people never connect to it: yerba mate, Ilex paraguariensis, used to brew a caffeinated tea across South America, belongs to the same genus as European holly, Ilex aquifolium, even though the European species is toxic if eaten in any quantity and has no such use.