Sexual reproduction in lichens depends on a germinated lichen spore, which contains only the fungal component of the lichen, encountering an appropriate alga on the substratum. This method involves a factor of chance. It is useful, therefore, for the lichen to have a mode of reproduction that ensures that the fungal and algal components of the lichen will come together to produce a lichen. Many of the asexual modes of lichen reproduction handle this problem by packaging fungal and algal cells together in a propagule that can produce a new lichen thallus. However, C. coralloides does not employ all of these modes of asexual reproduction. Also, not all propagules for asexual reproduction in lichens contain both the fungal and the algal components.
For example, pycnidia provide a mechanism for the asexual reproduction of Caloplaca coralloides in which the fungal component is not packaged with algal cells. Pycnidia are flask-like structures embedded in the thallus of the lichen which produce conidia, which can act as “spermatia” in sexual reproduction of the lichen, but which can also propagate the lichen asexually. A conidium is a fleck of fungal hyphae that can develop into a lichen if it lands on a suitable substrate, germinates and encounters an appropriate alga. Pycnidia occur in all lichen groups and are present in C. coralloides.
A type of vegetative propagule in some lichens that does contain both components of the lichen symbiosis is soredia. Caloplaca Coralloides does not have soredia (Arup 1995a). Soredia are small balls of hyphae (50-100 um in size) around a few algal cells. Soredia are formed in the photobiont layer, so they do not contain any cortex. They are released through breaks in the thallus cortex or they develop when the cortex of the thallus is damaged. Soredia can be carried from the surface of the lichen thallus by wind, water or animals. Masses of soredia that appear on the surface of the lichen thallus are called soralia.
Another structure for asexual reproduction in lichens is isidia. Isidia are coralloid or fingerlike projections from the upper cortex. Therefore, they are surrounded by a cortical layer. They are usually 0.3-1 mm in length and around 0.2 mm in diameter. When isidia are broken off they can grow into another lichen component. Isidia, like soredia, contain both the fungal and algal components.
The alga in a lichen reproduces asexually by mitosis and the formation of akinetes and aplanospores, spores resistant to harsh environmental conditions that germinate when conditions improve.
2005 Megan Kelso