1. Flowers ca. 3 (–4) cm long or shorter, double (stamens and pistil absent); bracts ca. 11–15 (–22) mm long.
1. Flowers ca. (4–) 4.5–6.5 (–7.2) cm long, single; bracts (12–) 15–26 (–32) mm long.
2. Stem erect, sometimes somewhat twisted toward tip, short (less than 0.5 m), usually ± densely pubescent; flowers white, produced only on peduncles arising within 10 (–15) cm of the ground, below any twisted portion.
3. Longer petioles ca. 5–9 cm; leaf blades with spreading basal lobes, widest at the lobes; introduced along railways.
3. Longer petioles ca. 0.5–2 cm long; leaf blades truncate to cordate at base, the widest part usually above the poorly developed lobes; native in dry, sunny sites.
2. Stem twining throughout, elongate; flowers pink or white, produced all along the usually glabrous or glabrate stem.
4. Sinus of larger leaves acute or rounded, with blade tissue extending essentially to the petiole (within ca. 2 mm).
4. Sinus of larger leaves ± square, the two main diverging veins forming the sinus lacking blade tissue on the lower side for ca. 2–9 mm from the petiole on either side (the sinus thus formed by the veins).
All species found in Calystegia
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. November 22, 2017. http://michiganflora.net/genus.aspx?id=Calystegia.