In message , P. van
Rijckevorsel writes
"P. van Rijckevorsel" schreef
http://www.box.net/shared/nc8vfa8m0m

or this one
http://www.missouriplants.com/Yellow...iola_page.html
PvR

I find Lactuceae a difficult group, especially when not in flower, but
both Sonchus oleraceus/asper*, what I've never completely convinced
myself is Sonchus arvensis and Lactuca seriola (= scariola) grow around
here and the original image looks more like Sonchus oleraceus than the
others. Anyway the spiny underside of the midrib is a good key character
for Lactuca seriola.

* I find some plants are obviously Sonchus oleraceus, some obviously
Sonchus asper, but many hard to place definitely in one species or the
other.
--
Stewart Robert Hinsley