They develop in telia (sing. telium, or teliosorus).
The telial host is the primary host in heteroecious rusts. The aecial host is the alternate host (look for pycnia and aecia). These terms apply when two hosts are required by a heteroecious rust fungus to complete its life cycle.
Teliospores consist of one, two or more dikaryote cells.
Teliospores are often dark-coloured and thick-walled, especially in species where they overwinter (acting as chlamydospores).
Two-celled teliospores formerly defined the genus Puccinia. Here the wall is particularly thick at the tip of the terminal cell which extends into a beak in some species.