1. Stem prostrate, with strong odor of ginger when freshly bruised; leaves in pairs; perianth regular, the tube very short, neither curved nor inflated but cup-shaped; stamens 12, with short filaments inserted on the ovary.
Asarum
1. Stem erect (herbaceous or a woody vine), with odor none or not ginger-like; leaves alternate; perianth bilaterally symmetrical, with elongate and inflated calyx tube; stamens 6, the anthers sessile and adnate to the stigma.
2. Plant a high-twining woody vine with flowers ca. 3 cm or more long; leaves usually more than 8 cm broad.
Isotrema
2. Plant herbaceous, not twining, with flowers less than 3 cm long; leaves (except the largest) less than 8 cm broad.
3. Flowers axillary; perianth ± straight, yellow; principal leaf blades about as broad as long or broader; escaped from cultivation, in ± disturbed places.
Aristolochia
3. Flowers on peduncles arising at the base of the stem; perianth S-shaped, purplish; principal leaf blades distinctly longer than broad; native, in forests.
Endodeca
All species found in Aristolochiaceae
Citation:
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 9, 2018. https://michiganflora.net/family.aspx?id=Aristolochiaceae.