In most groups of fungi, terminal or intercalary segments of the mycelium may become packed with lipid reserves and develop thick walls within the original hyphal wall. The new walls may be colorless or pigmented and are often hydrophobic. Structures of this type have been termed chlamydospores.
They have formed asexually. Generally, there is no mechanism for detachment and dispersal of chlamydospores, but they may become separated from each other by the collapse of the hyphae producing them.
They are therefore typical memnospores, forming important organs of asexual survival, especially in soil fungi. Chlamydospores may develop within the sporangiophores of some species of the Mucorales, e.g. in Mucor racemosus. The Glomales, which are fungal partners in symbiotic mycorrhizal associations with many vascular plants, reproduce primarily by large, thick-walled chlamydospores.
These develop singly or in clusters (sporocarps) on coarse hyphae attached to their host plants. They are sedentary in soil but may be dispersed by wind or by burrowing rodents that eat the spores.
Chlamydospores may also develop within the multicellular macroconidia of Fusarium spp. and may survive when other, thin-walled cells making up the spore are degraded by soil microorganisms.
Similar structures are found in old hyphae of the aquatic fungus Saprolegnia, either singly or in chains. In this genus, the chlamydospores may break free from the mycelium and be dispersed in water currents.
Chlamydospores which are dispersed in this way are termed gemmae. The term chlamydospore is also sometimes used to describe the thick-walled dikaryotic spore characteristic of smut fungi (Ustilaginales) but the term teliospore is preferable in this context.