On 28 May, 20:45, Rusty Hinge 2
wrote:
I understand that they were grown on roofs because it was believed they
kept lightning away.

That and it was good material for thatching. In France we call it
artichauds des montagnes. Not leek, but artichocke! Which is perhaps
closer to what it looks like. Tectorum, as in sempervivum tectorum,
means roofing.