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How do mushrooms grow so quickly?

by Timber Press on January 12, 2017

in Gardening, Natural History

Large, arbuscular mycorrhizal fungal spores. Image courtesy of Jim Deacon, University of Edinburgh.

Have you ever walked into your garden or through the woods to find a ring of mushrooms had sprung up overnight? In his third book on the soil food web, Jeff Lowenfels describes the reproduction and life cycles of fungi.


Fungi are often placed into one of two categories: perfect fungi are capable of making spores and can reproduce either asexually (with only one parent) or sexually (with two parents). Imperfect fungi reproduce only by asexual spores, or at least they have never been seen to reproduce sexually.

The most common type of fungal asexual reproduction is through the formation of spores that are dispersed from the parent organism. Some fungi develop sporangia, budlike cells that hold onto young sporangiospores until they mature and separate from the parent cell. Other fungi develop spores outside the reproductive cells. Still others create sclerotia, storage structures made up of compact fungal tissue, some of which can survive dormancy for long periods in adverse environmental conditions.

Fungi can also be asexually cloned from hyphal cuttings. Some mycorrhizal fungi form vesicles that can reproduce or clone the fungi. Still, nothing beats sporulation in terms of numbers. It is the reason fungi are so prolific and successful.

Sexual reproduction requires two mating types and can occur in several ways. In some fungal species, meiosis (nuclear division) occurs in the asci, single-celled spore structures, which results in the formation of exactly eight spores. These fungi shoot out their spores to distances of up to several centimeters. Given the size of the organism, this is comparable to tossing an American football a couple of miles (or kilometers). Consider the osmotic pressure that must be involved. In other species, basidia structures develop to produce and hold or eject spores. The pressure in this case is decidedly weaker. These tiny spores are dispersed by wind currents and can travel long distances.

One other point is important to mention. Scientists have discovered that fungi exchange DNA with other fungi and with other microorganisms. (Don’t be surprised, because human bacteria do it all the time.) They seem to do this based on environmental conditions that require some sort of adaptation. This has all manner of ramifications, many of which are being sorted out by lots of further study.

How mushrooms are formed. Illustration by Arthur Mount.


Some mycorrhizal fungi types (specifically, ectomycorrhizal fungi) form mushrooms, the specialized fruiting bodies that play a role similar to that of flowers in plants. Mushrooms can grow below the soil, as do truffles, or above, as do morels. Their caps can be gilled or nongilled. Some have economic and gastronomic value, such as porcinis and chanterelles. Not all mycorrhizal fungi produce mushrooms, although all mushrooms are fungi.

Mushrooms are typically the part of the fungus that carries and disperses fungal spores, usually through sporangia (sporangium, singular), the enclosures in which the spores are formed. Each tiny spore released from a sporangium gives rise to a hypha, which branches and grows into hyphae, which then continue to grow and interweave to form a mycelial web.

Sometimes the hyphae form rhizomorphs, structures that transport water and nutrients throughout the network. This occurs when parallel hyphae merge. The inner hyphae lose their nuclei and cytoplasm, becoming hollow.

Merging hyphae also form fruiting bodies as a result of hyphae growing together. Specifically, two homokaryotic fungal hyphae (each with genetically identical nuclei) merge cytoplasm, but keep their nuclei separate, to form a dikaryotic hypha. Every time the cell divides, the new cells keep the two sets of haploid nuclei separate.

At the appropriate time, given some cue from nature, some environmental condition stimulates the fungus, and signals are created in the circulating cytoplasm, which cause the hyphae to merge and form a primordium, a tiny knot in the mycelia. This primordium includes all the cells the mushroom will ever have. It enlarges into a tiny budlike structure, or button, which will grow into a full-size mushroom.

All a mushroom requires is water to fill the cells. The mushroom can rapidly pull in water from its mycelium and expand the primordium. It can take less than 24 hours for a primordium to fill and grow; this is why mushrooms can pop up so quickly. Mushrooms have outer membranes, or veils, that dehydrate rapidly, so they usually appear only when temperature and moisture conditions are right. Those hydrophobins are working full time.


 Jeff Lowenfels has been writing an award-winning garden column for the Anchorage Dispatch News for over forty years. He is the founder of Plant a Row for the Hungry, a program that encourages all gardeners to donate one row to feed the hungry. A popular national garden writer and leading proponent of gardening using the concepts of the soil food web, Jeff is the former president of the Garden Writers Association. He lives in Anchorage, Alaska, and Portland, Oregon.


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