This group of Wall Barley (Hordeum murinum) at the foot of a lamp-post was very eye-catching in the red light of dusk, though my camera could only gesture at it.
The next day I went back a couple of times to try again - a bit furtively, since the street corner is constantly overlooked and taking photos of weeds is obviously eccentric behaviour.
Wall Barley always seems to grow in places where dogs piss, but whether the unusual amount of red in these plants has anything to do with being pissed on, or with some other polluting accident (petrol, White Lightning), I don't know. (When nettles are pissed on it sometimes turns them pale yellow; dog-owners come to accept brown patches on their lawns.) [NB written a couple of weeks later: - In the Swedish fells I noticed a grass that I suppose was Poa alpina whose panicles were very strikingly coloured, sort of rosy-pink as well as strawy - I forgot to photograph it.]
And where did wall barley grow before human beings existed? Difficult to imagine it in Britain, - perhaps around a few dry rock exposures? - I rather imagine it was a latecomer from the dry south, eagerly colonizing our primitive clearings.
More or less unconnectedly, here are some plants whose anthocyanins went missing. This rather surprising plant is Herb Robert (Geranium robertianum), found in Savernake Forest.
(Here's what it normally looks like: - remember?)
And this plant is, of course, not White Campion (Silene latifolia) but white Red Campion (Silene dioica). Obviously in this case the context is a massive clue. The other clue is that a white Red Campion usually contains no anthocyanins, so its stem and calyx are pale green. By contrast, the white petals of White Campion are as a rule prettily contrasted with the wine-flushed calyces.
These are only probabilities. For two species so different in character and habit, (and in normal circumstances so instantly distinguishable), a cast-iron diagnostic difference is surprisingly hard to pin down. The main one concerns the capsule-teeth...
These ones are revolute not erect, proving the plant to be red campion. But you need to wait for mature fruit before you can see it.