- A hybrid between named taxa may be indicated by placing the multiplication sign between the names of the taxa; the whole expression is then called a hybrid formula.
- Agrostis L. × Polypogon Desf.; Agrostis stolonifera L. × Polypogon monspeliensis (L.) Desf.; Melampsora medusae Thüm. × M. occidentalis H. S. Jacks.; Mentha aquatica L. × M. arvensis L. × M. spicata L.; Polypodium vulgare subsp. prionodes (Asch.) Rothm. × P. vulgare L. subsp. vulgare; Salix aurita L. × S. caprea L.; Tilletia caries (DC.) Tul. & C. Tul. × T. foetida (Wallr.) Liro.
- It is usually preferable to place the names or epithets in a formula in alphabetical order. The direction of a cross may be indicated by including the sexual symbols (♀: female; ♂: male) in the formula, or by placing the female parent first. If a non-alphabetical sequence is used, its basis should be clearly indicated.