Apios, Fabricius, 1759

Egan, Ashley N. & Pan, Bo, 2015, Pueraria stracheyi, a new synonym to Apios carnea (Fabaceae), Phytotaxa 218 (2), pp. 147-155 : 152

Key to species of Apios :

1. Stipule 4 mm long or greater and plants of North America ............................................................................................................... 2

- Stipule 4 mm long (up to 6 mm in A. delavayai ) or less and plants of Asia ...................................................................................... 3

2. Stipule 4–6.5 mm long, pedicel 2–3 mm long, flowers deep maroon to pale maroon with white, standard 10.5–12.5 mm long....... ........................................................................................................................................................................................ A. americana

- Stipule 7–9 mm long, pedicel 4–5 mm long, flowers pale green suffused with rose purple, standard 12–15(–18) mm long............. ........................................................................................................................................................................................... A. priceana

3. Flower red, reddish purple, or orange; leaflets usually more than 5 cm .............................................................................. A. carnea

- Flower green, yellow, or purple; leaflets usually less than 5 cm ........................................................................................................ 4

4. Flowers paired on top of a single, common pedicel, corolla purple, leaflets oblong-linear to narrowly lanceolate, usually less than 1.2 cm in width............................................................................................................................................................... A. gracillima .

- Flowers each on their own pedicel, corolla light yellow to light green, sometime suffused with light purple, leaflets lanceolate to ovate-lanceolate or ovate, usually more than 1.2 cm in width ........................................................................................................... 5

5. Standard greater than 1.6 cm long...................................................................................................................................................... 6

- Standard less than 1.6 cm long........................................................................................................................................................... 7

6. Leaflets lanceolate, generally less than 2 cm wide, flowers 1–3 per node......................................................................... A. delavayi

- Leaflets lanceolate to ovate-lanceolate, 2–3.5 cm wide, flowers 2 per node ................................................................. A. macrantha

7. Leaflets ovate to rhomboid-ovate, flowers yellowish green or light green, keel coiled, style coiled, plants of China and Japan....... ............................................................................................................................................................................................. A. fortunei

- Leaflets ovate to ovate-lanceolate, flowers yellowish light purple, keel extended and inflexed but not coiled, style twisted, plants of Taiwan....................................................................................................................................................................... A. taiwaniana