Watercress Leaf Beetle Phaedon cochleariae

I'm not sure how widely the vernacular name is recognised. This one (Watercress Leaf Beetle) is used at the UK Beetles website, but NatureSpot uses an alternative name, Mustard Beetle.

These two were a mating pair collected from among at least 10 similar beetles on watercress. They both seemed to key to cochleariae but the first one I examined (the female) had more-or-less entirely black antennae, the only hint of colour on segments one and two being at the very apex of each segment. Also the diagram of the male's median lobe in Duff shows a very squared-off tip, whereas the tip of the one I collected was clearly rounded. The median lobe is strongly curved so if I laid it so the basal section was flat and the apex curved up towards the camera then it did appear squared off, but surely that's not a standard way of viewing it? Anyway, other sources (including Mike Hackston's ley and the German website coleonet.de) do not show the tip squared off.

female Watercress Leaf Beetle Phaedon cochleariae showing head, metasternum, pronotal fore margin, close-up of pronotal disc, apical sternite and spermatheca, Wendling Beck Environment Project (Norfolk, UK), 1st May 2024

male Watercress Leaf Beetle Phaedon cochleariae showing metasternum, pronotal disc and median lobe (3 views), Wendling Beck Environment Project (Norfolk, UK), 1st May 2024

I originally identified this one using Hackston's key and somehow managed to end up with calling it Phaedon amoraciae. I'd previously found an amoraciae (which I'm still happy with) but looking at the photos of this one now I think it's mroe likely to be cochleariae. There seeems to be some reddish on the first and second antennal segments - not much which I guess is why I didn't register it originally, but there shouldn't be any on amoraciae. Also compared to the one I'm still happy to call amoraciae, this one has very indistinct humeral calli and I think I can see a little irregularity in the lines of punctures on the side of the elytra (which Hackston has as a character for cochleariae). It was one of three but I only retained and examined this one.

However, the other cochleariae I've seen since (above) and most photos online, show a much more colourful beetle with clear blue-green reflections. This does not appear to have such strong colour tones so I'm wondering if I might have miskeyed it before getting it to genus, or if it could be amoraciae after all? Anyway, for now I think it's safest to leave it unrecorded until and unless I gain enough experience to be confident about what it is from the photos.

possible Watercress Leaf Beetle Phaedon cochleariae, North Elmham Cathedral Meadows (Norfolk, UK), 1st May 2024