this is called fasciation - its harmless, but you can prune out the affected stems if you want. Usual cause is said to be damage to the growing points earlier on, by frost, mechanical damage, insect damage, and possibly some viral cause as well. Funny, they look just like rhubarb stems...

thanks for quick reply,probably frost the culprit but have no rhubarb!

Keep a check out in your borders, I get a lot of fasciation to all sorts of plants. It amazes me and I love the quirkiness of it. As Bamboo says, it's quite likely due to the frosts we had. And I've already had an anemone with a double head. A daff with no trumpet but a small flower at the back. and a lily martagon with droopy leaves and a flat base to the flower.

all I've got is some pleating on leaves - cold when growing is the cause of that