Is it ekwisetum or equisetum?

In English a q is never alone. It travels with a u, and the pair make a single sound with two parts to it, a k followed by a w. Queen, quick, quiet, quantity. Somebody writing the sound down from scratch would have no reason to reach for a q at all, because k and w are perfectly good letters and they say exactly what is happening. The q is here because the word is Latin, and in Latin the sound was written that way from the beginning. The first half of the name is equus, a horse, and it is the same syllable that gives English equestrian and equine.

A c that has to be read as k, because the letter behind it is a Greek kappa.