H.2.1. 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.
Ex. 1. Agrostis L. x Polypogon Desf.; Agrostis
stolonifera L. x Polypogon monspeliensis (L.) Desf.;
Salix aurita L. x S. caprea L.; Mentha aquatica
L. x M. arvensis L. x M. spicata L.; Polypodium
vulgare subsp. prionodes (Asch.) Rothm. x subsp. vulgare.
H.2A.1. 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 ({o+}:
female;{o!}: male) in the formula, or by placing the female parent
first. If a non-alphabetical sequence is used, its basis should
be clearly indicated.