– one of the most common lichen symbionts – occurs in the thalli of more than 20 lichen genera. The most common photobionts in this genus that associate with Cladonia are A. glomerata, A. italiana, and A. mediterranea, with some lineages showing dominance in one or several climatic regions. The algal genus Trebouxia, a very common lichen photobiont, has not been recorded associating with the Cladoniacae. Some Pilophorus species associate with cyanobacterial symbionts (in addition to their association with green algae) in structures called cephalodia. The cyanobacterial genera Nostoc and Stigonema are involved in these tripartite associations. Development The development of several Cladoniaceae genera have been studied in detail, although the interpretation of results has sometimes been controversial. Cladoniaceae species begin development with the formation of a prothallus – a fungal layer upon which an algae-containing thallus will develop. It comprises the hyphae from the germination of an ascospore. After the protothallus contacts the alga, lichenization begins with the development of small squamules (scale-like thallus segments) that make up the primary thallus. Most Cladoniaceae have a mixed thallus, consisting of two parts: a base, parallel to the substrate, called the primary thallus and the other erect, the secondary thallus. The primary thallus is squamulose (scaly) or crustose (crustose-like). The secondary thallus consists of vertical structures that are shrubby and hollow, although they can be solid in rare cases. If these structures are made of generative tissue, they are called podetia; when they are made of vegetative tissue, they are called pseudopodetia. The morphology of these structures determines to a large part the taxonomy of the Cladoniaceae, which can range from simple to very complex branching patterns. Cladonia minisaxicola, found in the mountains of Bahia (Brazil) is the only species in that large genus that is completely crustose and does not develop podetia. The tips of the podetia have a wide range of morphology in the Cladoniaceae. They can be straight, tapering from a wide base to a point (called subulate), or flaring on cup-shaped scyphi. The scyphi are sometimes closed, or have a central perforation, forming structures called funnels. The podetia are slow-growing, with an annual growth rate generally ranging from 1 to 15 mm. Habitat and distribution Cladoniaceae species have been recorded growing in many habitats and on a diversity of substrates, including soil, tree trunks, and rotten wood. In a few cases, Cladoniaceae can grow on rocks, such