Catalan verb morphology displays a curious and complex morphome that is not morpho‐syntactically motivated. The set of categories represented consists of (a) and (b): (a) 1st singular present indicative, present subjunctive; (b) Past perfective indicative (synthetic), past subjunctive, past participle. The morphome is generally marked by a velar consonant: /k/ after a sibilant, /g/ elsewhere. I explore the spread in individual verbs of the velar marker from submorphome (a) to sub‐morphome (b) or from (b) to (a), and from the original verbs to others, in a corpus of inflections from 1200–1550. I attempt to identify morphological, phonological, and possibly semantic, motivations for the observed spread of the morphome from 22% of e‐conjugation verb roots showing any stem alternation in 1300 to 78% in the present day.