And being on willow, they would be Macraltica (often placed as a subgenus of Altica). I'll need to find my key to this group to key it further. Note the transverse sulcus on the pronotal base - a character all Altica possess.

is not evident in all species of Altica. Look at Altica foliacea here for example and Altica chalybea from the same site.

Rob, I looked through all of the Altica I've collected over the years and although I found specimens where the sulcus is not evident from a direct dorsal view the sulcus is there but shallow and needs a slightly different angle for the light to catch it. All of my A. chalybea have a strong sulcus though. By no means do I consider my viewpoint to be the end-all of facts. The sulcus (or lack thereof) is used in keys to alticine genera so I guess there are species of Altica where the lack of a sulcus is normal. I have my suspicions though that if those species without a sulcus are carefully studied that it will be discovered that there are actually two genera under the same name. But that is just my thoughts on it. Systematics, by the nature of the fact that all things continue to evolve, is constantly changing as well. What is a good genus or species one year may not be so the next.

Yes, we´ll probably never fully understand a lot of these cryptic species complexes. I agree there could well be two genera involved. Macrohaltica are generally bigger and slower and I think they deserve genus status.

As you say yourselve the sulcus is not allways evident, especially not in all live pictures. Very shallow sulci will often not appaer on a photo

All we can do is make the best of what we can see on the pictures

Cheers

Rob

Yep. BTW I am in awe over your knowledge base! It's good to have someone with so much to share.