Urocystis colchici  

A smut fungus on the leaves and petioles of Colchicum autumnale in the UK, visible as elongate lesions, often merging together, which rupture to expose powdery black masses of spores.

Sori in leaves and petioles as slightly elevated, pustular, elongate areas of various size and shape, often confluent, visible on both sides of the leaf, initially lead-coloured and covered by the epidermis which ruptures exposing the powdery, black mass of spores. Infection systemic. Spore balls globose, subglobose, ovoid to irregular, (15-20)-40 µm in diam., composed of 1-3(-4) spores and a more or less complete covering layer of sterile cells. Spores globose, subglobose, ovoid, irregularly oblong or subpolyhedral, 9-14.5(-15) x (11-)12-20(-23) µm, medium reddish brown, smooth. Sterile cells subglobose, ovoid to irregular, 510 x 6-15 µm, pale yellow, with smooth, 1-2 µm thick wall, collapsed in old specimens.

Description adapted from Vánky, K. (2012). Smut fungi of the world. St. Paul, Minnesota: APS press.

Map of known distribution in Great Britain and Ireland.