Lichens

thumb|A tree covered with leafy foliose lichens and shrubby fruticose lichens

thumb|250px|Yellow pseudocyphellea on the underside of a species of Pseudocyphellaria in Patagonia Pseudocyphellae (singular pseudocyphella) are structures in lichens that appear as tiny pores on the outer surface (the cortex) of the lichen. They are caused when there is a break in the cortex of the lichen, and the medullary hyphae extend to the surface. Pseudocyphellae are the same colour as the medulla of the lichen, which is generally white, but can be yellow in some species of Pseudocyphellaria and in Bryoria fremontii. The presence/absence, abundance, colour, and shape of pseudocyphellae

thumb|right|Lower cortex of Peltigera praetextata showing rhizines In lichens, rhizines are multicellular root-like structures arising mainly from the lower surface. A lichen with rhizines is termed rhizinate, while a lichen lacking rhizines is termed erhizinate. Rhizines serve only to anchor the lichen to their substrate; they do not absorb nutrients, as plant roots do. Characteristics of the rhizines are used to identify lichens, for example, whether they are dense or sparse, uniformly distributed or clumped in specific areas, and straight or branched. Only foliose lichens may possess rhizin