They aren't. Like mr lochroma said, it's prickly lettuce. But many other edible weeds (like dandelion) have little spines, and they never stopped anyone a tort before
Yes, lots of different genera with milky stems, prickles and composite, dandelion type flowers.
Milk thistles are 'Silybum' (honestly).
Sow thistle is 'Sonchus'
Prickly lettuce is 'Lactuca' from the Latin for milk.
Dandelion is 'Taraxicum'
There are others.
Your torts should love it.
The greeks here and especially my Tidgy go crazy for any of these.
And they're good in a balanced diet and the torts don't seem to bother about the spines at all.