Key to species of the Pteronia adenocarpa group

1. Cypselae glabrous-glossy, glandular and/or hairy, when hairy then hairs evenly distributed on the surface ...................................... ............................................................................................................................................................ remaining species of Pteronia

- Cypselae hairy, hairs strictly confined to the base .............................................................................................................................2

2. Branches glabrous ..............................................................................................................................................................................3

- Branches hairy ....................................................................................................................................................................................5

3. Branches greyish-white; leaves slightly keeled; cypselae glabrous on the surface.......................................................... 6. P. viscosa

- Branches greenish; leaves flattened; cypselae glandular on the surface ............................................................................................4

4. Leaves narrowly ovate, free, glabrous, apex with prominent cluster of bristles; capitula pedunculate; pappus biseriate, straight..... ................................................................................................................................................................................... 2. P. armatifolia

- Leaves oblanceolate or obovate, connate at base, punctate, apex without prominent cluster of bristles; capitula sessile; pappus multiseriate with a tortuous band near the base........................................................................................................ 1. P. adenocarpa

5. Involucral bracts puberulent; cypselae glandular on the surface; corolla brown ................................................. 5. P. stoehelinoides

- Involucral bracts and cypselar surface glabrous; corolla yellow........................................................................................................6

6. Branches setose; cypselae oblong ...................................................................................................................... 4. P. hutchinsoniana

- Branches pubescent; cypselae ovate............................................................................................................................... 3. P. elongata