A few of these have popped up this year in and around my greenhouse near Mainz, Germany. From googling, it looks to me like an "All the Year Round Lettuce", which I've never planted. Leaves are currently about 10-20cm long. Much obliged if anyone can confirm exactly what it is.
The colours don't look quite right to me but sessile leaves (attached direct to the trunk) with a relatively very strong midrib (slightly U-shaped in cross-section) from which the two sides fold slightly towards one another looks lettuce-like. However for me it is the stalk that is most convincing. That is not shown in this image of a Jericho:
but that bend looks very familiar (perhaps from planting too shallow or in a windy environment).
Yes, it is a lettuce.