Diagnostic key for Alternanthera species occurring in Saudi Arabia

1. Leaves lanceolate (ratio length/width: 4–5) ...................................................................................................... Alternanthera sessilis

1. Leaves ovate to obovate (ratio length/width: 1–2).............................................................................................................................2

2. Leaves obtuse to rounded; tepals 5.0–7.0 mm long, obtuse; fruit 1.5–1.8 mm long....................................... Alternanthera pungens

2. Leaves acute to acuminate; tepals 2.0–2.5(–3.5) mm long, acute to acuminate; fruit 1.8–2.2 mm long.. Alternanthera bettzickiana