Aristolochiaceae

The Aristolochiaceae () are a family, the birthwort family, of flowering plants with seven genera and about 400 known species belonging to the order Piperales. The type genus is "Aristolochia" L.
Description.
They are mostly perennial, herbaceous plants, shrubs, or lianas. The membranous, cordate simple leaves are spread out, growing alternately along the stem on leaf stalks. The margins are commonly entire. No stipules are present. The bizarre flowers are large to medium-sized, growing in the leaf axils. They are bilaterally or radially symmetrical.
Classification.
Aristolochiaceae are magnoliids, a basal group of angiosperms which are not part of the large categories of monocots or eudicots. As of APG IV (2016), the former families Hydnoraceae and Lactoridaceae are included, because exclusion would make Aristolochiaceae in the traditional sense paraphyletic.
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Phylogeny Group, place the family Aristolochiaceae in the order Piperales, but it is still quite common, though superseded, for the Aristolochiaceae to be assigned, sometimes with some other families, their own order (Aristolochiales).
Phylogeny.
Four assemblages can be distinguished in the genus-level cladogram of Aristolochiaceae:
Phytochemistry.
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" species are carcinogenic to humans.
Genomics.
The complete plastid genome sequence of one species of Aristolochiaceae, "Hydnora visseri", has been determined. As compared to the chloroplast genome of its closest photosynthetic relatives, the plastome of "Hydnora visseri" shows extreme reduction in both size (ca. 27 kilo base pairs) and gene content (24 genes appear to be functional). This Aristolochiaceae species therefore possesses one of the smallest plastid genomes among flowering plants.
Ecology.
Pipevine swallowtail butterflies lay their eggs on pipevine ("Aristolochia" species), and the larvae feed on the plant, but are not affected by the toxin, which then offers the adult butterfly protection against predators.
Fossil record.
The oldest fossil leaf remains are of †"Aristolochites dentata" from the Late Cretaceous of Nebraska, United States. Pollen record of †"Aristolochiacidites viluiensis" has been described from Upper Cretaceous sediments of Siberia. Fossil wood is known from the Deccan Traps of India some 66 million years ago. Leaf fossils of "Aristolochia" are known from the Early and Late Tertiary of North America and the Late Tertiary of Abkhazia, Ukrainia and Poland. Fossil leaf remains of †"Aristolochia austriaca" have been described from Late Miocene sediments of the Pellendorf site at the Vienna Basin in Austria. †"A. austriaca" is most similar to the extant Mediterranean species "A. rotunda" and "A. baetica".