From Sir Nigel by Sir Arthur Conon Doyle, creator of Sherlock Holmes
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.
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.
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.
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.
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!
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.
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.
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.
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.
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.
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.
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.
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.
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
• 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).