这些符号由四个相邻的大写字母组成，没有点分隔，后面也没有句号。作为第四个字母的字母X表示与各自属的任何物种有关。当考虑一个属的不同物种所呈现的特征差异时，第四个字母是物种名称的第一个字母。附件包含符号代码。

These symbols are composed of four adjoining capital letters, not separated by points and not followed by a full stop. The letter X as the fourth indicates that any species of the respective genus is concerned. When characteristic differences presented by different species of one genus are to be taken into account, the fourth letter is the first of the species name. The Annex contains the code of symbols.