letting nature back in

No, I didn’t find fungus growing in bird’s nests, but a fungus that resembles bird’s nests. Very tiny nests to be sure, and within each nest-shaped cup nestles a cluster of egg-like capsules.

Easy to overlook, the tiny bird’s nest fungus cups are clustered together growing on soil rich in decomposing wood including sawdust

The first time I paid attention to the tiny bird’s nest fungus was only in March this year. I was watching a small pollinating fly when my eye was attracted to the shiny fluted cups that are only about 1 to 1.5 cm (around half an inch) in diameter. Down on my hands and knees I was amazed to see that within the delicately fluted cups were nested small dark capsules resembling eggs, about the size and shape of small and slightly flattened peas.

Here is a slightly closer look. Some of the cups appear to be empty, but most contain several round egg-like capsules

I realised that these little cups belonged to a fungus, and I wondered at the capsules as I had thought that fungi spread by means of microscopic spores. Once I found out that these little fungi belong to the bird’s nest fungus family I was able to learn more about their curious nest shape and the little ‘eggs’ within.

Here is a close-up the little nest-like cups, with only one containing visible egg-like capsules in its centre

Although bird’s nest fungi were first scientifically described as far back as 1601 and they attracted subsequent interest from fungus experts, it was only in the 1920s that the mechanism for how these fungi disperse their spores was first understood.

The entire fruiting body comprises the cup (peridium) that houses the round capsules (peridioles). Interestingly, the word peridiole derives from the Greek word peridion, meaning “small leather pouch”, which is descriptive of the capsule containing its cargo of spores. Each peridiole contains spores that must be dispersed in order for the fungus to reproduce.

I think the bird’s nest fungus in our garden is Cyathus striatus, the fluted bird’s nest fungus

So how do the peridioles/capsules get to release their cargo of spores? In the 1920s it was discovered that the cup-shaped “nest” is actually a splash cup. When a rain drop falls into the cup hitting the wall of cup at a suitable angle, by means of a splash mechanism the velocity of the falling drop discharges the peridiole/capsule so that it launches at speed out of the cup and flies off to a distant spot from where the spores can disperse when the peridiole/capsule ruptures.

The capsules in the Cyathus genus of bird’s nest fungi have an added mechanism, in that each capsule carries with it a funicular chord that unravels when the capsule hits an obstacle such as a plant stem and if possible the chord wraps around the obstacle so that the capsule remains elevated above the ground. When the capsule ruptures, its elevated position enables a more effective dispersal of its airborne spores.

In brighter light the striated cups of the fluted bird’s nest fungus Cyathus striatus shine with a silvery iridescence 

I think that this rather wondrous diminutive bird’ nest fungus fulfills the criteria of being both odd and marvelous to qualify as a backyard curiosity. Added to its remarkable splash-dispersal discharge mechanism, the fungus itself is an efficient feeder on decaying and decomposing wood and other organic material and contributes to nutrient recycling and soil building – an asset to any garden.

To view high-speed videos of water droplets causing the ejection of capsules from the bird’s nest cup see this article by Hassett et al (2013).

Sources:

Alchetron. 2018. Cyathus. https://alchetron.com/Cyathus; Hassett, Maribeth O. et al. 2013. Splash and grab: Biomechanics of peridiole ejection and function of the funicular cord in bird’s nest fungi. Fungal Biology 117(10): 708-714. https://doi.org/10.1016/j.funbio.2013.07.008; Wikipedia. 2020. Nidulariaceae. https://en.wikipedia.org/wiki/Nidulariaceae

Posted by Carol