lichens

Lichens are a symbiotic combination of a fungus and an algae. The fungus generates the body of the lichen known as the thallus protecting the algae from detrimental environmental stresses such as dessication. The algae provides the nutrients via photosynthesis.

There are three main forms of growth: (a) Crustose - firmly attached to the substrate and not easily removed, (b) Foliose - leafy, possible to lift away from the substrate, often have root-like hairs and (c) Fruticose - Attached at one point and bushy. Sexual reproduction occurs by spores in the fungal portion of the lichen that must then find an algal partner in order to create another lichen. The fruiting body aids in identification and fall into three main types: (a) Podetia - stalks or cup-shaped bodies, (b) Perithecia - black flask-shaped bodies, (c) Apothecia - disc or 'tart'-shaped fruits that sit on the surface. Two forms of apothecia fruiting bodies occur: (i) Lecanorine - possesses an edge to the structure formed from the fungal cortex resembling a pastry crust to a 'jam tart' and is the same colour as the thallus, (ii) Lecideine - the fungal cortex is not raised at the edge and the edge is a different colour to the thallus. Asexual reproduction can also occur from propagule that contain both algae and fungal cells permitting rapid production of another lichen. The propagules may be of two main types: (i) Isidia - pin-like projections from the thallus, (ii) Soredia - powdery granules generated from elongated ruptures on the thallus surface.