Northern Tooth

Welcome to the final Mushroom Monday of 2025. We’ll end with a large and easy-to-identify species that hasn’t been recorded all that often on the Island: Northern Tooth (Climacodon septentrionalis).

As we’ve seen throughout this series, mushrooms come in all shapes and sizes, and can share physical traits without being closely related. The spore-bearing surface of Northern Tooth has spine-like ‘teeth’ rather than gills, folds, or pores (inset photo). Despite this, it is more closely related to the Polypores than other toothed fungi like Hedgehogs or Bear’s Head Tooth. Mushroom guides generally group species based on appearance rather than genetics – we’re looking at form in the field, not taxonomy – and so you’ll usually find Northern Tooth among the Toothed Fungi rather than the Polypores.

I wish I had known that the first time I came across this mushroom a few years ago. Not long before, I’d found some Hedgehogs (Hydnum spp.) and learned that everything in that group is edible. Being new to mushrooms, I thought that meant all toothed mushrooms were edible, and I got very excited at a big find of Northern Tooth. Fortunately, I double-checked (as I always do!) and quickly learned that while this species is not considered toxic, it is too tough and bitter to eat.

Northern Tooth forms large, overlapping brackets on the sides of hardwood trees, including Beech, Birch, and Maple (main photo). It starts out white but begins to turn yellow and brown with age. Unlike some of the other Polypores we’ve looked at – Red-Belted Polypore or Artist’s Conk for example – Northern Tooth isn’t perennial; the mushrooms in this photo will die by winter, and new ones will appear next year if conditions are right.

This is one of our parasitic fungi. Those fruiting bodies you see release spores that are carried by wind and water to new trees. Where there is an opening – a frost crack, branch scar, or other wound, for example – the fungus gains entry, grows mycelia inside the tree, and starts digesting lignin in the heartwood. Lignin is important to wood’s strength, and Northern Tooth slowly weakens the tree until it eventually breaks or blows over.

Once you see Northern Tooth brackets on the outside of the tree, the fungus is well-established, rot is underway, and the tree can’t be saved. That may seem like a bad thing, but this fungus is important to creating habitat for all sorts of things: other fungi, plants, insects, salamanders, bats, squirrels, and insect-eating and cavity-nesting birds, among others. In nature, parasites aren’t always negative: sometimes they’re the neighbourhood building contractor!

As if that weren’t cool enough, Northern Tooth is also carnivorous. It creates droplets that immobilize and kill tiny worms called nematodes. Over a period of days to weeks, the fungus envelopes and digests the nematodes. This serves two roles: it provides Northern Tooth with added nutrition (particularly nitrogen) and kills an enemy that would have preyed on the fungus. This adaptation isn’t unique to Northern Tooth, and more than 700 species of fungi have been found to be carnivorous.

Northern Tooth is a distinctive fungus that’s most often seen in fall. It may be more common on the Island than reports suggest, so keep your eye out for it as you explore PEI Untamed!