16 January 2014

On my way to somewhere else I found…

It’s hard to believe these mushrooms represent the largest living organism but they’re the outward and visible sign of a subterranean and under-bark network.

The network can be quite large, as described here on Wikipedia:  “The largest living fungus may be a honey fungus of the species Armillaria ostoyae [now called Armillaria solidipes].  A mushroom of this type in the Malheur National Forest in the Blue Mountains of eastern Oregon was found to be the largest fungal colony in the world, spanning 8.9 km² (2,200 acres) [and] estimated to be 2,400 years old.  … If this colony is considered a single organism, then it is the largest known organism in the world by area.”

And so it was named the “Humongous Fungus.“

There are many species of Armillaria, all with dark shoestring-like rhizomorphs that grow through the soil or under bark and white mycelial fans which spread under bark via root contacts and root grafts.  Here’s what they look like: rhizomorphs on the left, mycelia on the right.  (For a sense of scale, these are tree trunks)

Sometimes the mycelia are luminescent and cause foxfire!

Fascinating as their huge size may be, Armillaria spreads widely, infects many trees and can either kill them outright or be a contributing factor to their demise.  This diagram shows how it cycles through the forest.

I have seen Armillaria in Schenley Park without realizing what it was: rhizomorphs, mycelia and mushrooms.

So now I understand how a live tree can just fall over when infected by Armillaria root rot.

(photo credits:  mushrooms by Walter J. Pilsak via Wikimedia Commons (click on the image to see the original).  Rhizomorphs and dead tree on grass by Joseph O’Brien, USDA Forest Service via Bugwood.org.  White mycelial fan by Borys M. Tkacz, USDA Forest Service via Bugwood.org)

‘Tis the season for kissing under the mistletoe but this genus is too small for the purpose.

Mistletoes are parasitic plants in the sandalwood family.  The ones we associate with kissing, Phoradendron leucarpum and Viscum album, are evergreen plants that parasitize oak and apple trees.  In winter they look like green balls in the bare trees.  Click here for a photo and description.

Dwarf mistletoe, on the other hand, is amazingly small.  Arceuthobium’s 42 dioecious species parasitize only conifers.  The female plant of American dwarf mistletoe (Arceuthobium americanum) is shown above, the male below. Notice the tiny size of the plant relative to the pine needles.

Dwarf mistletoe begins its life as a seed that lands on a tree branch, then germinates and grows beneath the bark, sucking water and minerals.  It rarely kills the tree but the tree fights back by developing witches’ brooms or losing branches as shown on this lodgepole pine.  Foresters hate dwarf misletoe.

Many mistletoes depend on birds to spread their seeds, but dwarf mistletoe takes matters into its own hands.  During the 18 months of seed maturation, water pressure builds up in the seed capsule until it finally bursts out, traveling at almost 50 mph … like this!

Pow!  The size of a grain of rice, it can travel 65 feet!

Tiny but powerful.  Watch out below!

(all photos are American dwarf mistletoe, Arceuthobium americanum, from Bugwood.org: 1241494 by John W. Schwandt USDA Forest Service, 2141082 by Brytten Steed USDA Forest Service, 2250003 by Frank Hawksworth USDA Forest Service, 5367211 by Mike Schomaker Colorado State Forest Service)