This orange-streaked bramble stem caught my eye today.
Bramble Rubus fruticosus agg. hosts a few species of rust fungi but, as far as I know, only one which looks like this. These longditudinal pustules are the uredinia (stage II) of Kuehneola uredinis.
The UK species inventory lists its preferred common name as Pale Bramble Rust, with Bramble Stem Rust also in use. But they're both rather unsatisfactory. At this stage in this species' life cycle you can see it's very much not 'pale'. And at other stages of its life cycle you'll find it on growing on the bramble leaves, not the stem. So I'm inclined to forget the common name for this one.
I think you can get away with identifying this species from its field characters, but I did have a look at the uredospores.
- P. bulbosum should have paraphyses, but I can't figure out what they'd look like.
- P. bulbosum uredospores are 'distantly echinulate' whereas in K. uredinis they're 'densely and finely verrucose/echinulate.
|Reproduced from 'British Rust Fungi' by Wilson & Henderson (1966).|
Wilson & Henderson treat Grove's K. albida as synonymous with K. uredinis; but that uredospore illustration in Grove looks suspiciously like Wilson & Henderson's illustration for P. bulbosum. Hmm... Confusing!
The Plant Parasites of Europe website has images of K. uredinis uredospores (here) but no comparable photos for P. bulbosum.
I got this other micrograph of my collection, which shows something spotty, i.e. a 'verrucose' or 'echinulate' uredospore? I don't know why it's clear (hyaline) – did the fungus produce an empty spore for some reason? Maybe the other ones look like this too but you can't see the details of the uredospore wall usually, against the orange contents...?
- Also P. bulbosum is described as 'yellow' and K. uredinis is 'orange-yellow'. Well, I would describe my collection as 'orange-yellow' but that's not much to go on.
Location: Home, West Sussex