A horde of bees.
An angry wolf.
All these can be done as well. You could consider them 'damage over time' as well...
???
V
Trying to get a grip on the finer points of spell design...
Sorry to leap into the discussion just to gainsay you, but in fact magi of House Merinita can do this with one of their Inner Mysteries (Spell Timing). They have to cast the spell as a Ritual, so it's not so good for combat, but it can be made to recur indefinitely.
In this particular case, if I were the storyguide I might allow Reylar's spell (Level 20, D: Conc), but I'd rule on it like so: each round, he makes a Concentration roll. If he succeeds, it is as if he cast the spell again; the target loses another Light Wound. If he fails, the spell ends and he must actually cast it again.
No problem! To be honest, I'm pleased to see that such a mechanic does exist-- but it's not a baseline effect, which is what spurred the discussion.
In response to Vrylakos, regarding bees, wolves, boiling water or acid-- these things are all different than a straight PeCo spell. Perhaps I should clarify my comment:
"There's no baseline mechanic available to all Hermetic Magi for creating a repetitive, damage-inflicting spell effect that would not otherwise naturally continue to inflict damage."
With the other spells, you're generally creating something, that in its perfect state, would continue to do terrible things. They will continue to do their perfect natural behavior, until the duration ends. Fire burns, acid dissolves, bees sting. With PeCo, as we mentioned, you're creating a wound. A wound is just a wound. In its essential nature, it does nothing more except perhaps cause pain. It certainly doesn't cause more wounds just by being. That's the rub.
One of the best ways to think of spells is like a simple sentence:
"I verb (target or object) [possibly at some other target or object] {until X period ends}."
This spell becomes "I repeatedly injure targeted person until I stop concentrating," but we have the 'repeatedly' adverb in there-- that's not part of the vocabulary for Hermetic spells unless, as Erik pointed out, you're an initiated Merinita or other properly learned cultist. The adverb is necessary for the spell, otherwise it would just create a wound that couldn't be healed until the concentration was up (or the healing spell was cast with sufficient penetration to override the wounding spell.)
Not to say that such a mechanic should be considered 'broken,' it just needs to be adjusted for. 
Apparently the adjustment is to have the spell be a ritual and the caster initiated into the mystery that has learned spell timing.
-Ben.
This spell seems more like cloak of flame .
Oh, whoops, I wasn't very clear, was I? I was pointing out that the Merinita can make spells that recur, but I was also saying that I didn't think it was broken for a non-Merinita to make a spell like I was describing. Since the magus could always just cast the spell again each round, it doesn't seem like a bad thing to allow him to do so with a concentration roll if the spell is increased to D: Conc.
And sadly, this suddenly becomes a moot point as Reylar Valerian is removed from the game by an angry mob of townsfolk, who see him bleed blue blood after leaving the Baron's hall, where he pleaded his case for the ownership of his magical scytale, but incidentally mentioned the snake had been stolen for him by the King of the Black Forest, who may or may not be his father...
He cries out to his father for aid as the mob pulls him down, and a hurricane of blackened pine needles and wings pulled him into the sky.
V
And here I was starting to enjoy the 'Wilson' of the forum...
Ah well, I'm sure your player's next magus will be just as entertaining. 
-Ben.
The Valerian Clan is doubtless very extensive.
Leylar , Teylar and even Geylar could make appearances at some later stage.