KEYS TO SPECIES IN THE USA [pdf]
by William R. Anderson and Christiane Anderson
Key to specimens bearing flowers [fruits]
1. Flowers cleistogamous, minute (up to 1.5 mm in diameter), without visible petals, stamens, or styles.
2. Plants often decumbent with branches ascending; larger leaves 8–23 mm wide, 1.3–2.5 times as long as wide.
2. Plants erect or nearly so; larger leaves 2–8 mm wide, (3–) 3.3–7 (–8.3) times as long as wide.
1. Flowers chasmogamous, large (at least 6 mm in diameter), showy with visible petals, stamens, and style(s).
3. Styles 1 in each flower.
4. Petals abaxially densely sericeous, 4 pinkish white, the fifth distally pinkish white and proximally lemon-yellow; stamens 10, all fertile; exotic locally naturalized in southern Florida.
4. Petals glabrous, yellow, sometimes with red claws or blotches or turning orange or red in age; stamens 2–5, 2 or 3 fertile, the others, if present, reduced to staminodes without anthers; native in southwestern US.
5. Petals lemon-yellow; slender wiry twining vines.
5. Petals carrot-yellow; erect subshrubs or perennial herbs or decumbent, non-twining perennial herbs.
6. 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.
6. 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. Styles 3 in each flower.
7. Petals lemon-yellow, sometimes suffused with red or turning orange or red in age.
8. Petals glabrous; sepals all without abaxial glands; styles slender and subulate with minute stigmas; suffrutescent herbs or small shrubs.
8. Petals abaxially white-sericeous or -tomentose; sepals (4 of the 5) bearing pairs of large multicellular glands on abaxial surface; styles uniformly stout their whole length, with a large stigma on the internal angle; woody vines or shrubs with scandent or trailing branches.
7. Petals pink or pink and white, lavender-pink, white, or red.
9. Habit a woody vine, climbing high in trees; exotic locally naturalized in southern Florida.
9. Habit an erect shrub or subshrub; species native in southern Florida and southern Texas.
10. Inflorescences terminal, racemose; pedicels sessile; stipules intrapetiolar; leaves eglandular; styles slender and subulate with minute stigmas; Florida.
10. Inflorescences axillary, umbels or corymbs; pedicels raised on well-developed peduncles; stipules interpetiolar; leaves usually bearing 2–4 glands embedded in abaxial surface of blade; styles stout, cylindrical, truncate at apex with large stigmas; Texas.