Many of the native tribes in Roman Britain, and Scotland (which the Romans never conquered), were then fairly recent incomers. But at the time everyone agreed that one tribe in present-day Scotland had been there since the year dot. That was the Taezali, who occupied the eastern coastal strip of the highlands, and were presumably one of the Pictish tribes.
It is all too easy to invent spurious word associations, because there are only so many vowels and syllables. But I sometimes wonder if the thistle, the present emblem of scotland, and also called the teazel (which sounds quite similar to “thistle” come to think of it), wasn’t derived from their tribal name or vice versa. Perhaps they cut their hair short, or flat on the top, and the name Taezali meant something like “Thistle Heads”!
Maybe in addition to their body painting, which gave rise to their Latin name “Pictae” (Painted People), they also dyed their hair purple like punk rockers, making them resemble thistle tops even more!