Just got over one of those before the same race. It wasn't nice and very frustrating and I may have jumped back into things a bit too quickly in preparation for my goal race. I get the feeling its slowly shutting down on me so a week of enforced rest it is.
I found it hard myself but you've just got to try and get out a keep the fitness up somehow.
Was given antihistamine tablets and told to notbuse suncream actually as adding chemicals to the mix can irritate further. Also told to leave blisters to go down on their own rather than lancing. So keeping myself covered for the next week. Docs not able to do much it seems just relieve any pain thats there.
If it is indeed that plant its not common I think we may have just been unlucky after the weather and it may have ended up overhanging a path.
The sap damages the epithelial cells of the skin and removes any uv protection it has. This causes very painful blistering on top of the area, which in my case already hurt enough. Can also give you photo- sensitive vision and the scaring that it sometimes leaves behind can take years to heal and be allowed exposure to sunlight again.