AN INTRODUCTION TO LICHENS
Lichens are composite organisms, each consisting of a fungus species that has succeeded in establishing an ongoing parasitic relationship with a green alga or cyanobacteria. The fungus is dominant and the name of a lichen is really the name of its fungal component. There are about 400 species in New Jersey.
Like typical fungi, many lichens produce spores, embedded in disc- or knob-shaped structures called apothecia. But since spores replicate only the fungus component and not the algae it needs for survival, spores are not a very effective means of lichen reproduction. Many lichens, therefore, propagate partially or entirely by various vegetative methods. Some species produce dust-like particles called soredia, each particle of which contains a fragment of fungus and a few algae cells. Other species produce larger outgrowths called isidia, which break or are rubbed off the parent thallus; unlike soredia, these isidia have a cortex. A few lichen species appear to propagate only by fragmentation, breaking into pieces when stepped on or handled roughly. These vegetative particles can be carried by wind or water to new sites and grow into a new lichen.
Lichens in general can vary a lot within a species with regards to form. This is particularly true of the members of the genus Cladonia, in which some specimens, even "good" specimens, cannot be identified visually with 100 percent accuracy. To complicate things further, there are "chemical species" which are identical morphologically and which can be identified only by chemical tests. But many common lichens - especially the foliose and fruticose species - can still be identified from a good photograph with a fair level of accuracy provided you have a well-developed specimen.
The flat grayish, greenish, or yellow foliose lichens
on tree trunks and other objects require a close view of the upper surface for identification; look particularly for flat, disc-shaped fruiting apothecia; for areas of granular isidia; or for areas or lines of fine dust-like soredia erupting from the surface or along the edges. Some species have hair-like cilia fringing the thallus. It is very important to include something in a photograph to show scale; the width of the lobes that fringe the lichen thallus is a major field mark. Note that some species of gray or brown lichens become greenish if they get wet (the cortex becomes translucent and the algae beneath it show through). Photograph them when they are dry.
Many of the lichens on the ground or rotting wood are in the fruticose genus Cladonia. They have a basal growth of very small leaflets called squamules from which are produced upright fruiting stalks that may be tipped with a spore-producing apothecium. The red-fruited "British soldier" lichen is a familiar example. Identification requires a close view of these fruiting structures as well as the basal squamules. Several species may grow together on suitable habitat, creating a "hash" which is difficult to interpret.
Crustose lichens may be visible only as grayish or brownish stains on the rock, wood, bark or concrete; but they still produce apothecia, usually disc-shaped, which are necessary for their identification.
There is no real field guide to the local lichens but there are some technical works.
Karl Anderson
Karlanderson6@aol.com