Puccinia sessilis is a fungal species and plant pathogen, which is also known as arum rust or ramsons rust. It commonly infects Arum maculatum and Allium ursinum causing yellow to orange circular patches on leaves. On the underside of the leaves, it produces raised orange aecia commonly covered in spores. It is common in Eurasia in the spring.
It was originally found on the leaves of Iris versicolor in New York, USA. Other plant species affected by this rust include Convallaria majalis, Dactylorhiza fuchsii, Dactylorhiza incarnata, Dactylorhiza majalis, Gymnadenia conopsea, Neottia ovata, Paris quadrifolia and Phalaris arundinacea.
A specialised form, Puccinia sessilis f.sp. narcissi-orchidacearum (now called Aecidium narcissi) is a cause of rust in daffodils (Narcissus) and also on various wild Orchidaceae species.