I can't really blame the Four Wise Clerks of Oxenford here, as z in Spanish is normally written only before back vowels: Spanish /θ/ is written za ce ci zo zu. So Zéspedes is an anomalous spelling.

In any case, l for z is far more of a blunder than c for z.

The genus name Lespedeza shows up in some translations from classical Japanese poetry, in lieu of the usual "bush clover," for hagi or L. japonica. It is one of the Seven Weeds of Autumn. (Blunderingly, translators insist on calling these the "Seven Grasses.")

I can't really blame the Four Wise Clerks of Oxenford here, as z in Spanish is normally written only before back vowels

I wouldn't blame Joe Blogger for getting it wrong, but isn't the whole point of the OED to get arcane trivia right?

'Joe Blogger'--I like that. But wouldn't 'Joe Blogs' be even better?

Much better. Kudos.

I can see a capital C being misread as a capital L, perhaps that's why the OED mentions the variety with 'C'? (Especially since it is pretty well conceivable that someone also wrote Zespedez as Cespedez, given the common rules for c/z spelling in Spanish.)

Yes, I imagine both variants were in use, and I'm not really blaming the OED for picking the one not currently in favor, just twitting them for their haughty adverb.

Just proves a corollary of McKean's Law.

The corollary being: "The snider you are about someone else's mistake, the greater the likelihood that you yourself are in the middle of making one."