Percival (1921) [reference] produced the first English-language monograph of Triticum, The Wheat Plant. Although out-of-date for its treatment of genetics and plant breeding, the taxonomic and morphological components of the monograph are still in use today. Percival was unusual for designating the wild species as progeniotrs of the domesticated species. His classification is presented here, in its original form with corrections in the authority citations.
| Species 1. |
| Triticum aegilopoides Balansa |
| Race I. |
| Triticum monococcum L. |
| Species II. |
| Triticum dicoccoides (Körn. ex Asch. & Graebner) Schweinf. |
| Race II. |
| Triticum dicoccum Schrank ex Schübler |
| Race III. |
| Triticum orientale Percival |
| Race IV. |
| Triticum durum Desf. |
| Race V. |
| Triticum polonicum L. |
| Race VI. |
| Triticum turgidum L. |
| Race VII. |
| Triticum pyramidale Percival |
| Race VIII. |
| Triticum vulgare Vill. |
| Race IX. |
| Triticum compactum Host |
| Race X. |
| Triticum sphaerococcum Percival |
| Race XI. |
| Triticum spelta L. |