The Liliaceae, or the lily family, are a family of monocotyledons in the order Liliales. Plants in this family have linear leaves, mostly with parallel veins but with several having net venation (e.g., Cardiocrinum, Clintonia, Medeola, Prosartes, Scoliopus, Tricyrtis), and flower arranged in threes. Several have bulbs, while others have rhizomes. Shade-dwelling genera usually have broad, net-veined leaves, fleshy fruits with animal-dispersed seeds, rhizomes, and small, inconspicuous flowers; genera native to sunny habitats usually have narrow, parallel-veined leaves, capsular fruits with wind-dispersed seeds, bulbs, and large, visually conspicuous flowers.
The lily family was formerly a paraphyletic "catch-all" group of petaloid monocots that did not fit into other families. It included a great number of genera now included in other families and in some cases in other orders, including Agavaceae, Alliaceae, Amaryllidaceae, Asparagaceae, Asphodelaceae, Hyacinthaceae, Melanthiaceae, Nartheciaceae, Ruscaceae, Smilacaceae, Tecophilaeaceae, Themidaceae, Tofieldiaceae, and Uvulariaceae, and members of the monocot orders Asparagales, Dioscoreales, and Alismatales. Smilacaceae appears to be the family most closely related to Liliaceae in its modern restricted sense.
The genus Calochortus, which includes the sego and mariposa lilies, and its allied genera are separated into a separate family Calochortaceae in some schemes, while others maintain them as a subfamily of Liliaceae, the Calochortoideae.
It is estimated that the family evolved 58 million years ago during the Early Paleogene.