The current International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code; Turland & al. in Regnum Veg. 159. 2018) prescribes how to form the genitive case for personal names that are not of Latin form and that end in a consonant other than er. Article 60.8(b) specifies that the genitive for masculine nouns is formed by adding ii (singular) or iorum (plural), and for feminine nouns by adding iae (sing.) or iarum (pl.). Thus, one would render the genitive of the personal name “Smith” as, depending on the gender and number, smithii or smithiorum, or as smithiae or smithiarum. Latin grammar books (e.g. LaFleur, Wheelock's Latin, ed. 7. 2011), however, prescribe a slightly different set of genitive endings for these nouns: namely, for masculine, i (sing.) or orum (pl.), and for feminine, ae (sing.) or arum (pl.). As many taxonomists have probably noted, these endings are used by the International Code of Zoological Nomenclature (ed. 4, International Commission on Zoological Nomenclature. 1999), resulting in names such as Paramecium woodruffi (honouring Woodruff, masculine) and P. grohmannae (honouring Grohmann, feminine). Therefore, by comparison, it would appear that the Shenzhen Code requires an extra i between the noun and its genitive case ending. This interpolated i is called a “stem augmentation” in Art. 60.8(b) and (d). Why does the Shenzhen Code apparently use different endings than those of classical Latin and the zoological Code? Actually, the Shenzhen Code uses the same endings as in classical Latin and the zoological Code. The difference is how the Shenzhen Code creates the stem of the noun to which the genitive endings are added. The process is thus: the surname “Smith” is first put into Latin form by adding ius, resulting in smithius. Note that this process gives rise to stem augmentation because the interpolated i is part of the newly latinized stem. The genitive is then formed by the normal rules of Latin grammar: the us is dropped, resulting in smithi, and then the appropriate genitive ending is added. If the word is a masculine singular noun, i is added, resulting in smithii; or if plural, orum is added, resulting in smithiorum. Nowhere is this process explained in the Code. It should be. Without an explanation, taxonomists will not understand how a stem augmentation arises. Also, they will not readily appreciate why names already of Latin form lack a stem augmentation and end in a single i, as when, for example, Hieronymus (meaning “Jerome”) is inflected with only one i, resulting in hieronymi. To address this deficiency in the Code, we propose the following amendments to Art. 60.8 clauses (b) and (d) and Ex. 17, and a new entry in the Glossary defining “stem augmentation”. “(b) If the personal name ends with a consonant (but not in -er), substantival epithets are formed by latinizing them with -ius, then dropping the -us and adding -i- (stem augmentation) plus the genitive inflection appropriate to the gender and number of the person(s) honoured (e.g. Lecard-ius, lecard-i-i for Lecard (m), Wilson-ius, wilson-i-ae for Wilson (f), Verlot-ius, verlot-i-orum for the Verlot brothers, Braun-ius, braun-i-arum for the Braun sisters, Mason-ius, mason-i-orum for Mason, father and daughter).” “(d) If the personal name ends with a consonant, adjectival epithets are formed by latinizing the personal name with -ius, then dropping the -us and adding -i- (stem augmentation) plus -an- (stem of adjectival suffix) plus the nominative singular inflection appropriate to the gender of the generic name (e.g. Rosa webbi-ana for Webb, Desmodium griffithi-anum for Griffith, Verbena hassleri-ana for Hassler).” “Ex. 17. In Rhododendron ‘potanini' Batalin (in Trudy Imp. S.-Peterburgsk. Bot. Sada 11: 489. 1892), commemorating G. N. Potanin, the epithet is to be spelled potaninii under Art. 60.8(b) because Potanin is first put in Latin form by adding -ius to create potaninius; then the genitive is formed by first dropping the -us to yield potanini- (the final -i- is the stem augmentation) and then adding the masculine genitive singular ending -i, resulting in the epithet potaninii). However, in Phoenix theophrasti Greuter (in Bauhinia 3: 243. 1967), commemorating Theophrastus, it is not spelled ‘theophrastii' because Rec. 60C.1 applies.” “stem augmentation. [Not defined] – the -i- at the end of the stem of a specific or infraspecific epithet derived from a personal name not already of Latin form and ending in a consonant. It results from latinizing the personal name by adding -ius (e.g. Smith to smithius), then dropping the -us to yield the stem (smithi-), to which is added the appropriate genitive ending (smithi-i, masc. sing.; smithi-orum, masc. pl.; smithi-ae, fem. sing.; smithi-arum, fem. pl.) (Art. 60.8(b) and (d)). Similarly, adjectival epithets are formed by first latinizing the personal name by adding -ius, then adding an adjectival suffix (-an-) to which is attached the appropriate nominative singular inflection.”