Which plant has more species, Zigadenus or Fallopia? 
Zigadenus: Zigadenus is a genus of flowering plants now containing only one species, Zigadenus glaberrimus, the sandbog death camas, found in the southeastern United States from Mississippi to Virginia. Fallopia: Fallopia is a genus of about 12–15 species of flowering plants in the buckwheat family, often included in a wider treatment of the related genus "Polygonum" in the past.
Fallopia