Many pathogens are still undescribed, and many species complexes remain to be split up. Here are some taxa that I would recommend collecting and submitting to a herbarium if you encounter them.
Known in the literature as “Entyloma ranunculi-repentis” like many other Entyloma on Ranunculus. This corresponds to complex Entyloma eburneum on iNaturalist. Entyloma is extremely rarely recorded on Water Crowfoots, with my specimens on Brackish Water Crowfoot Ranunculus baudotii being the only recent record I am aware of. They may be very host-specific as with other Ranunculus species, or it could be that the recent hybrid origin of some of the host species has meant the same species occurs on multiple hosts.
These are generally all recorded as Peronospora grisea, but are likely to soon be split up. It is worth submitting specimens to your local herbarium so each new species will be represented when they are split, particularly if you find it on a new host for your area. These occur on many different Veronica including the garden Hebes from Aotearoa/NZ.