Halliday & Matthiessen (2014: 644-5):
… in order for a lexical item to be recognised as repeated it need not be in the same morphological shape. For example, dine, dining, diner, dinner are all the same item, and an occurrence of any one constitutes a repetition of any of the others. Inflectional variants always belong together as one item; derivational variants usually do, when they are based on a living derivational process, although these are less predictable. (For example, rational and rationalise are probably still the same lexical item, though the relationship between them has become rather tenuous; but neither now goes with ration — rational is closer to reason, though not close enough to be considered the same item.)
In Landor’s lineI strove with none, for none was worth my strife
there is a strongly felt cohesion between strife and strove, suggesting that strive, strove and strife are one and the same lexical item.