The fall and winter rains have pushed our planting plans off schedule in recent weeks, but with the rain…we have the return of ‘Mushroom Mondays’!


Bird's Nest Fungus (Crucibulum laeve)

Last winter I looked high and low for any evidence of this fungus, but by the time I finally found one, the dry season was upon us, and the only specimens I found were already dessicated.

This year I’ve kept my eyes open since the rains returned, and now these tiny fungi seem to be growing everywhere.

Crucibulum laeve is in the Nidulariacaea family of fungi, and the most common species of bird’s nest fungus likely to be encountered in the San Francisco and Monterey Bay area.

Crucibulum are saprobic fungi, obtaining all their required nutrients from decaying organic matter.  Typically found on woody debris, they may rarely be found on larger logs.

The overall characteristics of this species make it clear how the common name ‘Birds Nest Fungus’ came about.  The main cup-shaped fruiting body, called the peridia, resembles a small nest, and toward the final stage of development, these ‘nests’ can be seen with spore-filled ‘eggs’.

This fungus resembles tiny birds nests, hence its common name

There are three distinct stages of growth of this fungus.  Being able to recognize each stage of growth makes it easier to identify this species throughout the winter months.  I’ve been watching a colony on some woody debris for the past few weeks, but on first encounter, it wasn’t obvious to my then untrained eye that they would eventually develop into the classic birds nest.  After observing this species throughout its life-cycle this year, I feel confident I could now recognize it anywhere.

The fruiting bodies of this species are initially yellowish, and grow 5-8 mm high, and up to 15 mm across.  They have a pillow to round shape at first, and appear to be capped with an ochraceous lid, called an epiphragm.


The cap on immature fruiting bodies of Crucibulum laeve is called an epiphragm



At this stage the epiphragm is almost orange in color

In the second, more mature phase, the fruiting bodies become more cylindrical with a narrowed base, and the thickness of the epiphragm decreases and turns a pale buff color.


As the fruiting bodies mature, the cap thickness decreases...


...and the epiphragm color becomes more pale

Maturing fruiting bodies of Crucibulum laeve

As the fungus matures further, the lid gradually disappears, revealing the tiny 1-2 mm white, to pale grey, ‘eggs’, called peridioles.  It’s the appearance of this final stage that gives this species the moniker bird’s nest fungus.


As the epiphragm deteriorates, the 'eggs' are revealed


The fruiting body second from the bottom is just starting to reveal its peridioles


The 'eggs' of this fungus species are more correctly termed peridioles

A distinguishing characteristic of species within the Crucibulum genus is that the peridioles are attached to the interior of the ‘nest’, called the endoperidium, by a simple funiculus, an adhesive cord of hyphae, which the ‘eggs’ use to attach themselves to woody debris.


If you look closely (click photo to enlarge) you can just see the hyphae attached to this peridiole

The cup-shaped nests act as splash cups, facilitating the dispersal of the eggs.  Once the lid has disappeared, when a raindrop strikes the cup at the appropriate angle, the eggs are projected out of the nest, stretching the hyphae until the egg breaks free of the cup.  The cord remains attached to one end of the egg, and the free sticky ends of the cord hold the egg to the leaf or stick where it becomes attached, and starts the cycle over again.


Once all of the 'eggs' have splashed out of the nest cups, the endoperidium is more readily visible

Species in the Nidulariaceae family, including Crucibulum, are considered inedible, not due to toxicity per se, but because they are not sufficiently fleshy to be culinarily useful.

Regardless, this is a common and rather charming species of fungus to kick off this season’s Mushroom Monday posts.  (For all of our fungus posts to date, see our Fungi blog category).  I expect our Mushroom Monday posts won’t be as regular this year, but that depends on how many new species we encounter compared to last year…we’ll have to wait and see what the rest of winter brings!