Key to identify Porophyllum species in the northwest of Argentina

1. Stems decumbent; plants gynodioecious; corollas dark purple.......................................................................................... P. iruyense

- Stems erect; plants monoecious or gynodioecious; corollas lemon, cream, greenish or brownish....................................................2

2. Leaves petiolate; leaf blades ovate-elliptic......................................................................................................................... P. ruderale

- Leaves sessile or attenuate into a pseudopetiole; leaf blades subfiliform, linear or elliptic ..............................................................3

3. Gynodioecious herb 9–25 cm tall; leaf blades linear-subfiliform to elliptic; capitula with pedicel remarkably inflated below receptacle, 2.5–3 mm in diam.; florets ca. 100; corollas cream ........................................................................................ P. cabrerae

- Monoecious herb 15–80(–130) cm tall; leaf blades linear to elliptic; capitula with pedicel slightly inflated below receptacle, 1 mm in diam.; florets 45–60; corollas lemon.............................................................................................................................. P. riparium