An isidium is a
vegetative
Vegetative describes vegetation. Vegetative may also refer to:
*Vegetative reproduction
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in ...
reproductive structure present in some
lichens. Isidia are outgrowths of the
thallus
Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or " twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...
surface, and are