by Don Culwell, SFNC docent
Those interesting, light and dark splotches on tree limbs and bark, some of which have curled up edges, some form little branching tree or shrub-like growths on limbs or on barren soil, they catch your eye. Some even grow in hanging masses from trees (like old cedars on a bluff) that cause one to wonder if what is being seen is Spanish moss. But, in Arkansas, it is most likely Old Man’s Beard, a lichen. And their colors, whether their growth is crusty, leafy, or branching, may be chartreuse, yellow, orange, or red; most often around central Arkansas they are seen as white to grey to blue-green, to black and even grey stalks with caps of red balls (which are British Soldier lichens).
These unique organisms are called “pioneer plants,” for they grow quite well on rock surfaces, tombstones, tree bark, and poor, bare soil where no other “plant” can exist…they are the first to inhabit many such surfaces in the ecosystem. They function in a symbiotic capacity, that is, they are made of fungal threads that we call “hyphae” and there are tiny rounded cells of algae all around and through their hyphal matt (a living association between two organisms, the fungus and the alga…we call this mass of cells a thallus). The algal partner here, being green, carries on photosynthesis when moisture is available, making carbohydrate molecules. The fungal hyphae provide a place, often a moist one, that “houses” the algal partner and absorbs carbs made by it. These lichens grow and prosper under good environmental conditions and quickly dry out when moisture is absent. Their mass of hyphae and algae grows, spreads its branching morphology, or flat, crusty mass, covering “pioneer surfaces” with their interesting patterns of growth.
Reproduction within these lichens takes on interesting characteristics. Asexually (vegetative reproduction), tiny particles we call soredia (tiny bits of lichen) are dispersed by wind, water, or animals through fragmentation of the thallus; tiny, ball-like structures called isidia are also produced for dispersal. Small (or very tiny) cups or saucer and plate-like structures (maybe as much as a half inch in diameter) may be formed on lichen surfaces; often these are of a brownish or darker color. It is from within these cup or saucer surfaces that spores of the fungal partner are made. Only the fungus is reproducing here by spore production (a sexual process) which spreads the fungal partner.
Lichens, like mosses, may be more obvious during the dormant, winter season…they are more obvious in ones’ line of vision with the leaves off the woody limbs. Take a walk in the woods and locate the crusty, the leafy, or the branched forms of lichen (crustose, foliose, and fruticose morphological forms). They will brighten your winter’s day!