The Aristolochiaceae, or the Birthwort family, are a family of flowering plants with 8 genera and about 400 species belonging to the order Piperales. The type genus is Aristolochia L.
The Aristolochiaceae are magnoliids, a basal group of angiosperms which are not part of the large categories of monocots or eudicots.
Some newer classification schemes, such as the Update of the Angiosperm Phylogeny Group, place the family Aristolochiaceae in the order Piperales, but it is still quite common, though superseded, for the Aristolochiaceae to be assigned their own order (Aristolochiales).
They are mostly perennial, herbaceous plants, shrubs, woody vines or even lianas.
The membranous, cordate simple leaves are spread out, growing alternately along the stem on leaf stalks. The margins are commonly entire. There are no stipules.
The bizarre flowers are large to medium-sized, growing in the leaf axils. They are bilaterally or radially symmetrical.
Many members of Aristolochia and some of Asarum contain the toxin aristolochic acid, which discourages herbivores and is known to be carcinogenic in rats. Aristolochia itself is carcinogenic to humans.
Genera of Aristolochiaceae on the PBS wiki are Aristolochia, Asarum and Saruma.