KEYS TO SPECIES IN THE USA [pdf]
by William R. Anderson and Christiane Anderson
Key to specimens bearing fruits [flowers]
1. Fruits fleshy, indehiscent.
2. Inflorescences terminal, racemose; pedicels sessile; stipules intrapetiolar; leaves eglandular; Florida.
2. Inflorescences axillary, umbels or corymbs; pedicels raised on well-developed peduncles; stipules interpetiolar; leaves usually bearing 2–4 glands embedded in abaxial surface of lamina; Texas.
1. Fruits dry at maturity, breaking apart into samaras or unwinged nutlets or cocci.
3. Mericarps unwinged, smooth or bearing at most a very short dorsal crest and/or lateral ribs.
4. Mericarps smooth, with thin brittle walls; sepals all without abaxial glands.
4. Mericarps with a dorsal crest and often lateral ribs, the walls thick and tough; chasmogamous flowers bearing 8 abaxial glands on 4 of the 5 sepals, the tiny cleistogamous flowers with all sepals eglandular.
5. Chasmogamous flowers borne in umbels of 4 terminating leafy shoots; plants often decumbent with branches ascending; larger leaves 8–23 mm wide, 1.3–2.5 times as long as wide.
5. Chasmogamous flowers borne singly in axils of full-sized leaves; plants erect or nearly so; larger leaves 2–8 mm wide, (3–) 3.3–7 (–8.3) times as long as wide.
3. Mericarps developing into samaras bearing obvious wings.
6. Each samara bearing 1 elongated dorsal wing, the sides of the nut smooth or bearing at most short winglets or crests.
7. Wing of samara with the adaxial edge thickened, the veins bending from it toward the thinner abaxial edge; slender wiry vine in desert shrubs; native in southwestern US.
7. Wing of samara with the abaxial edge thickened, the veins bending from it toward the thinner adaxial edge; woody vine climbing in trees; exotic species locally naturalized in Florida.
6. Each samara bearing 2 or 3 large lateral wings, the dorsal wing none or, if present, notably smaller than the lateral wings.
8. Lateral wings of samara 2, semicircular; dorsal wing well developed, like lateral wings but smaller; native in Texas.
8. Lateral wings of samara 3, elongated, much longer than broad; dorsal wing mostly lacking or at most a low rib, rarely 1 elongated winglet much smaller than lateral wings; exotic species locally naturalized in Florida.