They are now grown worldwide, and more than 400 cultivars have been produced. Some hybrids have become invasive species.

 The name is derived from the Greek words krokos (saffron) and osme (smell), referring to the saffron-like scent, when dried flowers are dipped in water. They have colourful inflorescences of 4 to 20 vivid red and orange subopposite flowers on a divaricately branched stem.

The terminal inflorescence can have the form of a cyme or a raceme.