Marchitar (Spanish for “to fade; to wither”) comes from the Latin marcere (“to decay, wither”) which itself comes from the ancient Proto-Indo-European root merk which also means the same, “to decay, wither.”
From the Proto-Indo-European root merk, we get the English… morning (via Old German — just remember the German morgen!).
Morning, after all, is just the end of the decay of the moon!
The m‑r root is clearly visible in both!