Clathrus ruber, called the basket or lattice stinkhorn, “must be smelled to be believed,” according to mycologist David Aora.

Bill Pramuk photo

Last November, I got into the topic of mushrooms and trees (Mushrooms: Another Kingdom Heard From, 11/5/16). The impetus was a sudden flush of mushrooms appearing soon after generous rainfall in October. Then, with a wet winter, mushrooms and other fungal fruiting bodies continued to appear and pique my interest.

The latest example was a strange surprise.

In a home landscape grove of coast live oaks, with the soil covered by a thick layer of wood chip mulch, I noticed something reddish and resembling the remnants of a dried up slice of tomato.

I looked at this thing and thought; “What in the world is that?’

On close inspection I saw others in various stages of development: a whitish, rounded mushroom cracking open to reveal the reddish framework inside. Another one, fully open, had houseflies congregating on it.

Intrigued, I got down close and got a whiff of rotten meat. No wonder the flies were all over it.

I decided I would just have to find out what it is.

With a little research, I found an article on it by the Bay Area Mycological Society (BAMS) with the subtitle: “I stink, therefore I am.” The mushroom is Clathrus ruber, the basket stinkhorn.

Checking further, I found it in David Arora’s book “Mushrooms Demystified.” He calls it the latticed stinkhorn.

Both descriptive common names refer to the openwork frame of the mature mushroom. Arora also compares it to a “red or orange whiffle ball.” He says: “It is, in my humble fungal opinion, the vilest of any stinkhorn. It must be smelled to be believed.”

The stench arises from a mucilaginous greenish spore mass, visible inside the lattice framework.

Strangely, like a few other mushrooms, the basket stinkhorn glows in the dark. The BAMS article comments that you “can view examples of mushroom bioluminescence in the privacy of your own home (or closet). It is unlikely that you would be able to remain for very long in a small, dark space with a mature Clathrus.”

So, what is this fungus doing here and is it harmful?

Like other fungi, the stinkhorns reproduce via microscopic spores, but how the spores of this heretofore unnoticed mushroom arrived in Napa Valley is a mystery to me. Arora says it is native to southern Europe. It has turned up in several southeastern States and is common in the parks in San Francisco.

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The BAMS article comments that Clathrus prefers temperate climates and seems to be advancing northward with global warming.

Clathrus does not cause disease or decay in trees. It simply absorbs carbohydrates from the moist wood chip mulch.

In contrast, another mushroom-like structure I have noticed growing in the mulch near Douglas fir trees indicates the probability of severe decay. This one is called the velvet top fungus (Phaeolus schweinitzii). It is rather showy in the red velvet stage as it expands but becomes brown as it dries out. One might mistake it for a cow pie.

Velvet top fungus causes a cubical brown rot in woody roots and trunks, rendering them structurally weak.

Yet another important one turned up on a tree inspection last week. A mature corkscrew willow had several large woody “conks” on the lower trunk. I recognized it as a Ganoderma, a fungus that causes white rot in the trunk and roots in many tree species.

Tapping the trunk with a mallet produced a hollow sound indicating decay has been advancing for a long time.

Be alert. We can learn a lot by paying attention to these tree associates.

Bill Pramuk is a registered consulting arborist. Visit his website, Email questions to or call him at 707-226-2884.