Neighborhood Mushroom Watch (Someone’s Got To Do It): Part III – Spore Release and Dispersal

“For the rain had ceased at last, and a sickly autumn sun shone upon a land,

which was soaked and sodden with water. Wet and rotten leaves 

reeked and festered under the foul haze which rose from the woods. 

The fields were spotted with monstrous fungi of a size and color

never matched before - scarlet and mauve and liver and black. 

It was as though the sick earth had burst into foul pustules; 

mildew and lichen mottled the walls, and with that filthy crop 

Death sprang also from the water-soaked earth.”

From Sir Nigel by Sir Arthur Conon Doyle, creator of Sherlock Holmes

The summer of 2016 in southern New England was mired in the most severe drought in nearly a decade. While everyone reveled in the near "perfect" weather, wells began to dry up, lakes became historically low and waterways withered into ponds and long stretches of exposed beds. Watering restrictions and bans were issued as some towns purchased water from the state's back-up reservoirs. Farmers lost millions in production, and officials declared many regions a natural disaster area.

Welcomed rains triumphantly arrived in late August, but it was too little, too late for stunted crops - but not so for fungi. As if waiting for the appropriate conditions, they responded with astounding speed to the call of wet weather by fruiting on forest floors, suburban lawns, tree bark, rotting stumps, decomposing leaves, wood mulch, compost and manure. The myco-celebration was brief, but it generated and released countless gazillions of spores throughout the night and before dawn. It's fungi's sole mission - species perpetuation assisted by gravity, wind, water, insects, mammals and ejection ballisitics.

With a Foul Stench, the Erotic and Vile, Rude and Provocative,
Shameless Mutinus Elegans Demands Your Fervant Attention

This is my third post on the fungi of New England in which I investigate various modes and mechanisms of spore release and dispersal. Part I (here) discusses fungal basics and their otherworldly lifestyles, while on a quest to study local members of Kingdom Fungi. Part II (here) is a "Summer Sampler" of some remarkable specimens that fruited overnight in my neighborhood.

MUTINUS ELEGANS - PUTRID GOO ENTICES AGENTS OF DISPERSAL
Emerging mysteriously overnight after three days of soaking rain, over two dozen M. elegans magically sprang up in gregarious clusters from a bed of decomposing wood mulch and leaf litter in my yard. Its genus name, Mutinus, refers to the Roman phallic deity, and its order name is Phallales, as one might expect. For obvious reasons, it’s commonly called the Dog Stinkhorn, Headless Stinkhorn and the Devil's Dipstick. A related and frequently mistaken species, Mutinus caninus, is more reddish in color and smaller. 

They're both edible but hardly tempting, although they've been used in potions and ointments for gout, epilepsy and gangrenous ulcers and fed to cattle in parts of Europe as aphrodisiacs (no surprise). Not uncommon among fungi (Penecillium is the best example), the stinkhorn possesses antibiotic (anitbacterial and antifungal) properties.

And plants at whose name the verse feels loath,

Filled the place with a monstrous undergrowth.

Prickly, and pulpous, and blistering, and blue,

Livid and starred with a lurid dew.

From "The Sensitive Plant" by Percy Bysshe Shelley, 1820.

The poet is "loathe" to include the name stinkhorn in verse.

The somatic phase of growth begins with the stalk's (stipe) emergence from a partially-submerged, creamy-white, two to three centimeter, egg-shaped volva that is attached to the soil by a thick mycelial cord. Within hours, the capless mushroom acquired almost five centimeters of height. The jaw-dropping spectacle is accomplished so quickly since the stinkhorn is fully-formed in a compressed state within the "egg" - its appearance related more to expansion than cellular growth. The stinkhorn's slightly curved and erect body is hollow internally with an orange peel-like, spongy external surface that is punctuated with minute interconnecting chambers. 




  
During the reproductive phase of growth, which quickly follows, the apex of the stalk becomes smeared with an olive-brown, fecal-smelling, mucilaginous slime (gleba). The malodorous goo is enriched with spores produced within the volva and passively exudes from a small opening at the tip during its erection. The lively color of the stinkhorn is visually enticing to insects as is the gleba, which is an offensive olfactory mix of skunk-smelling methylmercaptan and rotten egg-infamous hydrogen sulfide. The gelatinous mass of spores irresistibly attracts mycophagous (fungi-eating) insects such as the metallic-colored Bluebottle fly that traipse through and ingest it.

Rather than relying on wind and gravity to disperse the spores, the two commonest dispersal modalities for all fungal spores, the appendages and bodies of insects serve as vectors of dissemination. Called entomophilus dispersal, the cache of spores are unknowingly removed during its grooming elsewhere. Spore ingestion may also contribute to dispersal, since they're acid resistant and can germinate elsewhere following defecation.

In a day or two with its reproductive obligation fulfilled, the fruiting body has begun to wither, becoming limp and flaccid with little remaining gleba, yet a lone fly is still attracted by the fetid scent. Off to the left, also promoted to germinate by the wet weather, a bevy of tiny cup-shaped Bird's Nest fungi are awaiting the next rain to facilitate spore release via a uniquely different mode and dispersal mechanism.

CYATHUS STRIATUS - SPLASH-CUP RELEASE MECHANISM
Sprinkled around the stinkhorns and easy-to-miss by virtue of their tiny 3/8th inch-diameter, Bird's Nest fungi easily can catch the eye by their grouping into tight clusters on rotting wood mulch. Its fluted fruiting body resembles a miniature bird's nest replete with eggs, which are lens-shaped periodoles - packets of millions of spores and the specialized cells that form them. The "nest" (peridium) is a cup-shaped structure that quickly loses its membranous, lid-like cover structure (epiphragm) upon germination. 

Cyathus Striatus - A Master at Spore Dispersal
Initially, Bird's Nest fungi have immature fruiting bodies that are spheroidal with a hairy projections on the exterior and contain lens-shaped periodoles that contain spores. a striated interior.  When mature, the mushrooms rupture exposing the striated namesake-interior and appear like tiny eggs with spores enclosed within the protective sac of the periodole "eggs." They fruited in concert with the stinkhorns and like them, are saprophytic - enzymatically feeding on decomposing organic remains.

As do plants, fungi utilize two modes to extend their range: growth into a neighboring area, which is a slow process (fairy rings are an example) or the dispersal of spores utilizing various vectors. Compared to seeds, spores are microscopic (~2-5 μm), lighter, less dense and more aerodynamically-designed and can travel considerable distances via the wind - the dispersal vector to which most spores subscribe. 

The Mushroom is the Elf of Plants-

At Evening, it is not-

At Morning, in a Truffled Hut

It stop upon a Spot

From "The Mushroom is the Elf of Plants" by Emily Dickinson

A region of micro-still air surrounds the spore-producing gills of mushrooms, which spores that rely on the wind for dispersal must first clear. In addition, most fungi are below the thin, non-turbulent "boundary layer" of air at ground level. When air flows over a surface, such as the ground, friction reduces current flow and creates a transition zone of calm air between the two stable systems. In order to become airborne, many fungi have developed highly creative mechanisms for assisting spores to penetrate through the layer in order to utilize the wind for dispersal.

A Cluster of Bird's Nest Peridia Filled with Lens-Shaped Periodoles Awaiting the Next Rain
The Bird's Nest mature fruitbodies are cone-shaped and covered externally with shaggy, dark brown hairs, whereas, the inside wall is smooth, striated and gray and filled with lens-shaped periodoles. The fungus typically fruits on beds of decomposing woody mulch.

C. striatus has adapted to the problem of both discharge and dispersal beyond the boundary layer via ballistospory, by literally catapulting spores into the air. The Bird's Nest's "splash-cup" mechanism is accomplished when one-eighth inch raindrops travelling at 13 to 26 fps strike the cup and eject periodoles a foot or two from the "nest." Each periodole is attached to the cup's inner wall by a cord-like funiculus, which tears from the cup and serves as an attachment mechanism by entangling a sticky holdfast called a hapteron to a nearby plant. Once above the boundary layer, wind currents disseminate the spores. Voila!

The Innovative "Splash-Cup" Mechanism for Releasing and Dispersing Spores
 (A), Forceful raindrops strike the peridium; (B), Periodoles are ballistically ejected through the boundary layer; (C), The holdfast attachment snares onto anything in its trajectory; (D), Spore release and dispersion follows. 
Modified Images and Courtesy of Nicholas Money, Professor of Botany, Miami University.

FUNGI AT THE MICROSCOPIC LEVEL
Both M. elegans and C. striatus are members of phylum Basidiomycota. Along with larger, sister-phylum Ascomycota ("sac fungi"), they are members of the "higher fungi" sub-kingdom Dikarya, which is contained within Kingdom Fungi. Basidiomycetes (a non-taxonomic, obsolete class but convenient and informal term) produce most of the large fruiting bodies found in nature - the specialized reproductive structures that house basidia such as mushrooms, puffballs, bracket fungi, yeasts and so on. 

Its members largely reproduce sexually via specialized cavate (club-shaped), microscopic spore-producing and spore-bearing cells called basidia that typically blanket the gills located outside the fruiting body such as found on the underside of mushrooms. In the case of the Dog stinkhorn's volva and Bird's Nest's periodoles, spores mature inside the fruiting body instead of discharging them directly into the air. The internal production of spores accounts for the number of creative ways they are released in order to "get them outside." The gasteroid fungi were originally classified as gasteromycetes or "stomach fungi", another obsolete term of reference since many members are unrelated.

Cross-section of a Mushroom
Modified from nomadsonwheels.com 

Fungi are constructed of a thread-like network of mycelia (pl.). It's the whitish, fuzzy cobweb-like growth found on the forest floor beneath an overturned log. The mycelium permeates throughout the body of the fungus. On a microscopic level, it's comprised of an interconnecting and branching mass of tubular cells called hyphae (2-10 μm in diameter) that are responsible for the growth of the fungus and its nutrition. The hyphae and mycelium channel nutrients to form fast-growing fruiting bodies. 

SEM of Fungal Mycelium and Basidia with Spores
(Left), Mycelial mass of interconnecting and branching hyphae. It's role is to penetrate
(Right), Scanning Electron Micrograph of basidia and associated basidiospores. Basidiospores have a single haploid nucleus. 

COMING TO TERMS

Mutinus elegans typically appears on decomposing woody substrates, which makes it saprobic, obtaining nutrition from a dead or dying host. In contrast, plants are autotrophic, capable of providing and creating their own "food" (glucose) by converting carbon dioxide and water in the presence of sunlight (photosynthesis). Fungi and animals are heterotrophs, obtaining nutrition from their surroundings by secreting enzymes that break down (decompose) complex molecules into smaller, more absorbable compounds. Fungi digest foods externally via "chemoheterotrophic extracellular digestion" and then absorb it versus animals that ingest foods and digest it internally. Fungi are often parasitic, deriving nutrition from an unhealthy substrate such as a tree, and can continue as saprobic, after the host succumbs (or contribute to its demise). 

Along with soil bacteria, fungi are the great decomposers and recyclers of our terrestrial ecosystem. The disassembling of large organic molecules into simpler forms is a vital process that nourishes other life forms by re-entering the food chain. Without rot and decay there would be no life.

Fungi's Essential Role in the Ecosystem
The complex organic molecules of detritus (dead plant material, animal remains and fecal material) are broken down by decomposers such as fungi, bacteria and earthworms into inorganic derivatives such as carbon dioxide, water and minerals (such as nitrogen and phosphorus). Fungi decompose organic matter by releasing enzymes, after which they absorb nutrients made available within the decaying material while returning (recycling) carbon and nutrients to the ecosystem for other living organisms such as vascular plants for growth and replenishing carbon dioxide to the atmosphere.
Modified from biotrick.com

IN A KINGDOM OF THEIR OWN

The study and classification of fungi - mycology - was initially a naked-eye endeavor based on morphology and reproductive structures. It was originally a branch of botany, although fungi were always recognized as different from plants. The science became more exacting with the invention of the light microscope in the 16th century and far more precise with the advent of SEM (Scanning Electron Microscopy) and molecular genetics in the 20th century. It led to the placement of all fungi within Kingdom Fungi of which taxonomists have classified perhaps 140,000 types, but the numbers suggest that only 10% are known.

Fungi were originally included within Kingdom Plantae based on anatomical and lifestyle similarities such as vegetative growth (the period between germination and reproductive stages), nonmotility (rendered via firm attachment to a substrate), rigidity (although fungal cell walls contain the rigidity-conferring, carbohydrate-polymer chitin occurring in arthropod exoskeletons, whereas plant cell walls are made of cellulose and animals lack a cell wall) and seed-like spores (superficially similar to plant seeds but fungal spores are immensely different and of course animal seeds are gametes and totally different). Remember that superficial resemblances are not a reflection of phylogeny, only convergent evolution! 

Many Aspects of Fungal Growth are Plant-like
The striated and gilled mushrooms of Mycena leaiana are visible with the naked eye, and are thus classified as macrofungi, which are largely found in subdivisions Basidiomycota and Ascomycota, although many are capless. Growing laterally from the forest floor in clusters, Mycena, like many mushrooms, orient themselves via negative gravitropism (plants orient to the sun called phototropism), so that the spores fall directly downward but above the boundary layer. It also protects the developing spores from rain. Fungi are also capable of plagiotropism, in which the apical portion of the stem bends upward towards vertical and not just at the base.

Unlike plants, fungi lack true roots, stems and leaves, lack vascular tissue as do plants, and don't possess chlorophyll, and therefore can’t manufacture food via photosynthesis as do plants. And unlike seeds, spores are microscopic, unicellular, produced in far greater numbers and don't contain miniature plant embryos and food stores. Seeds and spores share haploidy and diploidy conditions (half and normal chromosomal numbers), but there are major differences regarding the ultimate goals of sporogenesis - mass production of spores versus fewer spores but with genetic variability (explained in post Part I here).

Fungi and the Phylogenetic Tree of Life
The three-domain system of life (Carl Woese, 1990), which uses ribosomal RNA protein sequences, adds a level of classification "above" kingdoms and divides life forms into Bacteria, Archaea and Eukarya. All life is theorized to have evolved from a "universal common ancestor." First classified as plants, fungi (red arrow) are thought to have diverged from plants and animals but are more closely related to the latter. Fungus-like slime and water molds, although structurally similar to fungi, belong to Kingdom Protista (Protoctista). Unlike single-celled bacteria and archaea that are prokaryotic (lack membrane-bound cellular organelles) and are classified within separate domains, fungi, like plants and animals, are eukaryotic (contain membrane-bound organelles, especially a nucleus).
Modified from Biology of Plants, Seventh Edition, W.H. Freeman and Company, 2005

WHO'S RELATED TO WHOM?

Most of the scientific community believes that dinosaurs and birds are phylogenetically related, as are mammals and reptiles, apes and humans, and so on. They all belong to Kingdom Animalia and, along with plants, are eukaryotes (organisms with cells that contain membrane-bound organelles, especially a nucleus). So, how are plants, animals and fungi related being in separate kingdoms? Is there a common ancestor?

Although relationships are unresolved, molecular analyses suggest a three-way split between between fungi, plants and animals estimated at 1,576 +/- 88 Ma and that fungi and animals were derived from a common ancestor that existed ~1 billion years ago. Subsequent to that, terrestrial colonization of land by fungi remains somewhat speculative and obscure (see Prototaxites below). No ancient fossils exist, since fungi don't biomineralize (produce preservable minerals within biological tissues). 

Plants and fungi exist in symbiotic relationships that are thought to have developed long ago. Co-operative interactions with fungi may have helped early plants adapt to the stresses of the terrestrial realm. Thus, it's likely that fungi were on land with plants in the Devonian, although molecular clock estimates indicate fungi gained ground earlier in the Cambrian. 

Fungal Columns of Prototaxites Dominate a Speculative Landscape
Although alternative older views suggest it was a large vascular plant, it is currently thought that, in the Late Silurian to the Late Devonian, Prototaxites formed large trunk-like structures up to 1 meter wide and 26 feet high, the largest organism of the period. It possessed a tubular structure identified in fossils most like fungi of phylum Glomeromycota and must have had an extensive mycelium to have obtained sufficient organic carbon to accumulate the necessary biomass for the giant fungus.
Used with permission from scientist F. Hueber (who redescribed Prototaxites as a fungus in 2001 after 20 years of research). Painting by M. Parrish with permission and courtesy of the Smithsonian Institution.

OMPHALOTUS ILLUDENS - BULLER DROP BALLISTOSPORY

Commonly referred to as the Jack-O-Lantern mushroom, for obvious reasons, and the fact that it fruits in the fall, Omphalotus illudens is saprobic, in this case deriving nourishment from the roots of an unhealthy acacia tree. It's typically found in large clumps on decaying wood, buried roots or at the base of hardwood trees in eastern North America. Its agaric (mushroom-shaped fruiting body) is bright-orange with decurrent (descending on the stalk) gills (thin plates beneath the mushroom cap that contain spore-producing basidia). Don't be enticed by the seductive, culinary beauty of the mushrooms. They are extremely poisonous when ingested!

Omphalotus spores are gravity-released from the undersurface of the fruiting body, which allows wind currents to disperse them called anemophilous dispersal. The large number of mushrooms in clusters (many of which reach six inches in width) and the massive numbers of spores that are generated (a large mushroom can shed 40 million spores per hour) better the odds that at least a few spores will germinate somewhere downwind if the conditions are right. How do the spores get off the gills and away from the mushroom cap?

All members of phylum Basidiomycota, such as the Dog Stinkhorn, Bird's Nest and Jack O'Lantern fungi, possess spore-producing basidia cells. As mentioned, they line the gills on the undersurface of mushrooms or equivalent reproductive structures. Each spore secretes a small amount of sugar that absorbs moisture from the humid air around the gills, which condenses on the spore's surface in a thin film. Condensed water also forms a tiny Buller's drop at the base of the spore at the sterigma, a tiny extension of each basidium (sing.) As the drop gradually increases in size, it suddenly contacts the film and quickly collapses as it "feeds" additional moisture to the spore's surface. 

The micro-event shifts enormous mass to the spore providing sufficient momentum to accelerate the "ballistospore" 25,000 times the force of gravity and discharge it through the micro-thin boundary layer of air around the gills to the wind. By comparison, the NASA Space Shuttle possesses a maximum acceleration of only a few times the force of gravity. The mechanism of ballistospory is utilized in many unrelated mushroom groups and is the result of parallel co-evolution.

(Top), Time-Lapse Photos of Micromechanical Forcible Discharge of a Spore Using a Buller's Drop
The transfer of energy from the drop to the spore releases the spore from its supporting structure. During the early phase of coelscence process, the sterigma provides the external force that prevents the spore from moving toward the drop. In the late phase of the coalescence process, the sterigma is now put under tension and should fracture easily to prevent dissipation of the spore energy. The kinetic energy of the spore after ejection ejects it through the boundary layer. 
From Xavier Noblin et al, 2009.
(Bottom), High-Speed Video Imaging Demonstrating Ballistospore Discharge
From YouTube

There is no known analog in nature of this unique, musculature-less, micro-mechanical process in animals, plants or bacteria. The production of many trillions of spores ensures that some will survive once dispersed by the wind. Some basidiomycetes lack forcible discharge such as the stinkhorns that use insect vectors, which is considered an evolutionary loss ancestral to all basidiomycetes.

PARASOLA PLICATILIS - AUTOLYSIS OF THE FRUITING BODY
Subsequent to genetic investigation, many coprinoid fungi - all members of Basidimycota - have been reclassified, many with a name change. In fact, binomial scientific names of all fungi often change with the advent of more refined genetic analyses. This is true especially of "gill" fungi. 

With Parasola plicatilis, the group acquired the coprinus genus name, because they frequently "live on dung", while plicatilis in Latin means "folded" or "wrinkled". Although this sole, delicate beauty fruited one morning on wood chips, they are also purported to live in grassy areas and forest litter. With a delicate, long stalk, cover of tiny hairs and a gracefully unfurled parasol, P. plicatilis doesn't remain too long in the heat of the day. There's a reason, and it's related to spore release and dispersal. 

As the mushroom matures, the stem begins to rapidly elongate followed by liquefaction of the cap and gills within hours via the mushroom's autolytic enzymes. "Self-digestion" allows the mushroom's black spores to release to the wind, facilitated by the elongate stalk well above the boundary layer. The blackish goo that forms following lysis provides the group's more common name "inky caps", which actually can be used for writing. 

GANODERMA AUSTRALE - GRAVITY DOES ITS THING
This common perennial, semicircular-shaped, large fungus protrudes in a shelf-like manner from its host, a rotting stump. G. australe's spores are produced inside tiny, rigid tubes rather than gills that line the underside of the fruitbody. They open to the exterior and lend a perforated appearance to the fungus, hence the species common name polypore and bracket fungus due to its shelf-like growth on the sides of trees and stumps. Unlike mushrooms that morph into a putrefying mass in days following the reproductive phase, bracket fungi can last months, through winter and some years owing to their woody consistency.

Various Spore-bearing Surfaces Under Caps
Modified from maturehealth.files.wordpress.com

It's parasitic in early stages (fungal tree pathogens produce biodelignification or white heart rot in oak, birch, beech, chestnut and a few others) and becomes saprobic as the host dies (which can have enormous economic and environmental impact). They're commonly called "conks", because the fungal "wood" is corky in texture with a tough, leathery and shiny surface (ganoderma means "shining skin"). Not surprisingly, they're inedible, although some members of the genus have been used to make tea and for medicinal purposes in China and Japan for thousands of years. 

With a drab, brownish uppersurface, the brilliant white, rounded collar and undersurface are an indication that brown spores are ready to be released by basida that line the tubuli. Succumbing to gravity, they have colored the fruiting body, adjacent bark and underlying soil with a fine, brown dust upon their release. You can even ascertain the direction of the prevailing wind to the east from the color of the adjacent bark.

The Shelf or Bracket Fungus Ganoderma Australe
Growing on trees that are naturally elevated from the ground, a stalk is unnecessary to elevate the fruiting body above the boundary layer's still air. Success of germination is ensured by the enormous number of spores that are generated over the many years that the fungus can live, which often can be calculated by counting the growth zones or furrows on the cap as the cap extends outward and downward. 

SCLERODERMA CITRINUM - WINNING BY THE NUMBERS
In contrast to mushrooms and like the aforementioned stinkhorns and bird's nest fungi, S. citrinum produces spores inside the fruit body. It's often confused with puffballs, which are soft and spongy when ripe, Scleroderma ("hard skin") citrinum is an earthball fungus. Superficially, the two are similar but are unrelated. Also known as Common Earthball or Pigskin Poison Puffball, it's typically found found solitary or in groups in the woods on rotten wood and leafy, twiggy ground. 

Because they are often partially buried, they have been mistaken as truffles, a non-farmable ascomycete fungus that is highly prized for its culinary attributes. That would an unfortunate mistake for the forager, since earthballs have an unpleasant flavor and are mildly poisonous causing GI disturbances, chills and sweats. It would be financially beneficial to recognize the difference in the field, since this year a 4.16 pound white truffle sold at a Sotheby's auction for $61,250. And yet, it was a bargain, since abundant rainfall in Italy has produced a bumper crop that brought prices down.

S. citrinum is yellow-brown in color and covered with a scaly raised and ornamental mosaic of attractive brownish geometrics on its tough, rind-like peridium (skin). It typically has an ellipsoid or globose (round) to pear-shaped fruit body that contains trillions of spores that develop within locules (small cavities or glebal chambers). Unlike puffballs that are saprotrophs, earthballs are mycorrhizal ("fungus-root"), entering into a symbiotic relationship with vascular plants. 

In fact, over 90 percent of all plant families are known to partner with mycorrhizal fungi. By doing so, the fungus provides increased water and nutrient absorption while deriving carbohydrates formed from photosynthesis. It often explains why crops fail and why a newly planted sapling doesn't "take." Gardeners recognize this from their active use of compost.
  

Typical Fine-Branching Mycorhizzal NetworkContrary to one's common perception, the white fungal network of hyphael cells in intimate contact (ectomycorhizzal, outside of root cells and penetrating within, endomycorrhizal) with the roots of vascular plants and trees is responsible for the uptake of nutrients, not the plant roots.
From motherearthnews.com and illustrated by Michael Rothman

S. citrinum's is a member of Basidiomycota, but unlike mushrooms it's spore-producing basidia cells line and mature within the puffball's enclosed, globular interior. It's 
considered to be a gasteroid ("stomach") fungus for obvious reasons. Puffballs, when provoked by rain, implode and release trillions of spores to the wind in a powdery, smoke-like puff through a small aperture on the the superior surface of the fruiting body. On the other hand, earthballs, which also rely on a massive release of spores, develop fissures when ripe in order to release their bounty.

PUNCTELIA APPALACHENSIS - GONE WITH THE WIND
Instead of parasitizing or scavenging other organisms, some 13,500 fungi to date have discovered farming by being intimately involved in a symbiotic relationship. It's a mutualistic and intimate partnership with dissimilar organism(s). The affiliation allows the lichen to endure extremes of temperature, nutrient availability, solar radiation and aridity, seemingly everything adversely environmental with the exception air pollution. As a result, lichens are typically not found in big cities ("lichen deserts") and industrial regions due to high levels of sulfur dioxide.

There is a low mist in the woods—

It is a good day to study lichens.

From A Year in Thoreau's Journal by Henry David Thoreau, 1851.

The interdependent partnership is between a mycobiont, a lichenized fungus (the major partner and usually a member of Ascomycota), and a photobiont, a green alga or cyanobacteria (formerly called blue-green algae) or both. The mycobiont derives organic molecules (generally simple carbohydrates such as glucose) from photosynthesis carried out by the photobiont, while the alga is protected against desiccation and excessive solar radiation, and receives mineral nutrition from the mycobiont's atmospheric and substrate surfaces. Cyanobacterial partners provide nitrogen to its fungal partner.

Schematic Cross-Section of a Typical Foliose Lichen
Arranged in a layered sheet-like manner, a foliose lichen's thallus consists of: 1.) A colorful upper cortex of interwoven, highly-compacted, physically-protective ultraviolet light-filtering pigment of fungal hyphae); 2.) A green or blue-green algal photosynthesizing photobiont surrounded by the strands of the mycobiont; 3.) A spongy, middle medulla of loosely-packed, thread-like hyphae; 4.) A lower cortex of; 5.) Anchoring hyphae on the substrate (rhizines) without vascular capabilities like plants. The thallus of a lichen is the vegetative, non-reproductive "body" of the lichen. Other lichens possess a somewhat different morphology such as a missing lower cortex.
Modified from Wikipedia, artist JDurant and www.autocww2.colorado.edu/~toldy2/E64ContentFiles/AlgaeAndFungi/Lichen.html

Very common in deciduous woods and forests of New England, foliose Punctelia appalachensis is accompanied by various tiny crustose lichens was growing on a rotting log in my back lot (below). The lichen has a greenish, mineral-gray thallus (vegetative body) with divided lobes and non-ciliated ("hairy") margins. Notice the green photosynthetically-active center section. That classifies it as a chlorolichen, whereas a lichen with a cyanobacterial partner is a cyanolichen. 

A Large Foliose Lichen Shares a Decomposing Log with Numerous Diminutive Squamulose Forms
This Punctelia appalachensis is covered with spores. Lichens are found in many growth forms: foliose (leaf-like lobes that are easily removed from the substrate), fruticose (shrubby or pendant), crustose (most common, crust- or coral-like and firmly-anchored by root-like rhizines), leprose (powdery) and squamulose (scale-like lobes).

Lichen reproduction is not a straightforward event, since lichens consist of two or even three distinct organisms that each participate in the process. Lichens reproduce asexually utilizing openings on the thallus called soralia that contain dust-like granular particles (soredia) and that contain fungal and algal cells from the parent lichen and grow into a new thallus. Alternately, tiny, cylindrical projections (isidia) on the surface that incorporate both mycobiont and photobiont can easily break off (fragmentation) and grow elsewhere on a suitable substrate.

Sexual reproduction occurs when lichens produce miniature-appearing, cup-shaped fungal fruiting bodies (apothecia) that contain spores and require the appropriate photosynthetic partner to lichenize. Our Punctelia specimen, being a member of Ascomycota (the other higher "true fungus" along with Basidiomycota and the most common mycobiont), asexually produces ascospores that take to the wind for dispersal. 

By the way, symbiosis exists between many other life forms. Jellyfish contain an alga (zooxanthellae) within their tissues as do reef-building coral, neither of which can survive on their own. It explains why jellyfish frequently swim inverted or dwell in shallow sunlit waters within the photic zone. Lichen's fungal members can't live and grow without their communal partner and are never found in nature without it, whereas, the photobionts, whether algal or cyanobacterial, can survive independently in nature. 

A DEDICATION
This post is dedicated to botanist, geologist, naturalist and fellow blogger Hollis Marriott, who always seems to like it when I post on something that grows. Please visit her blog par excellence "In the Company of Plants and Rocks" (here).

VERY INFORMATIVE RESOURCES IN PRINT

• Kingdom Fungi by Steven L. Stephenson 
• Macrolichens of New England by James W. and Patricia L. Hinds
• Mushroom by Nicholas P. Money 
• Mushrooms Demystified by David Arora
• Mushrooms of Northeast North America by George Barron 
• Mushrooms, Simon and Schuster’s Guide by Gary H. Lincoff

A FEW OF THE MANY EXCELLENT PAPERS ON-LINE
•  A Higher-Level Phylogenetic Classification of the Fungi by David S. Hibbett et al, Mycological Research III, 2007 (here).
•  Field Guide to Common Macrofungi in Eastern Forests and Their Ecosystem Functions by Michael E. Ostry et al, U.S. Forest Service, 2010 (here).
•  Mycelium Running by Paul Stamets, Ten Speed Press, 2005 (here).
•  Towards a Natural System of Organisms: Proposal for the Domains Archaea, Bacteria, and Eucarya by C.R. Woese et al, Proc. Natl. Aca. Sci., June 1990 (here).
•  Weathering of Rocks Induced by Lichen Colonization — A Review by Jie Chen et al, Elsevier, Catena 39,2000 (here).
•  Surface Tension Propulsion of Fungal Spores by Xavier Noblin et al, The Journal of Experimental Biology 212, 2009 (here).