Ground elder is most accurately described as an extremely invasive weed with a variegated ornamental form. The species (Aegopodium podagraria) is a fast-spreading ground cover that colonises borders and is very difficult to eradicate once established. The variegated cultivar 'Variegatum' is more restrained and attractive but still vigorous.
The flat-topped white umbel flowers are similar to elderflower and can be used as cut material. I would advise against growing this anywhere, as once it has jumped into a bed it is nearly impossible to eradicate without much effort, pain and heartbreak. You may even have to move.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Ground Elder Rust
Orange to brown pustules on the undersides of leaves, with yellow spotting on upper surfaces. Heavily infected leaves distort and die back.
Remove and bag infected foliage; do not compost. Improve air circulation by cutting back dense growth. Rust rarely controls the plant but can be reduced by clearing affected leaves promptly.