A search for 𝐸𝑟𝑦𝑠𝑖𝑝ℎ𝑒 𝑡ℎ𝑒𝑠𝑖𝑖 led me to its British stronghold in Oxfordshire, where I soon found it at Hartslock NR. This high-quality chalk grassland was also the site of my 4,000th species in the British Isles, a day shy of five months after my 3,000th and a couple of days before my 17th birthday.

𝑇𝑖𝑙𝑖𝑎 is practically unknown as a host for powdery mildew in the British Isles, so you can imagine my surprise when I found not one but two infected trees in an area of Woking yesterday. The infections are very sparse, causing discolouration and only on younger leaves.

𝐸𝑟𝑦𝑠𝑖𝑝ℎ𝑒 𝑎𝑢𝑠𝑡𝑟𝑎𝑙𝑖𝑎𝑛𝑎, specific to 𝐿𝑎𝑔𝑒𝑟𝑠𝑡𝑟𝑜𝑒𝑚𝑖𝑎, is rare in the UK but there is a population doing well at RHS Wisley which has been known from here in previous years. My first time seeing this stunning powdery mildew species!

Multiple species of Erysiphaceae occur on 𝑃𝑎𝑝𝑎𝑣𝑒𝑟, and are best separated microscopically. Shown here are 𝐸𝑟𝑦𝑠𝑖𝑝ℎ𝑒 𝑟𝑎𝑑𝑢𝑙𝑒𝑠𝑐𝑢𝑖 on 𝑃𝑎𝑝𝑎𝑣𝑒𝑟 𝑟ℎ𝑜𝑒𝑎𝑠 (which forms single conidia) and 𝐺𝑜𝑙𝑜𝑣𝑖𝑛𝑜𝑚𝑦𝑐𝑒𝑠 𝑏𝑜𝑙𝑎𝑦𝑖 on 𝑃𝑎𝑝𝑎𝑣𝑒𝑟 𝑠𝑜𝑚𝑛𝑖𝑓𝑒𝑟𝑢𝑚 (which forms catenate conidia).