Hydnum repandum

Hydnum repandum: A Sweet Tooth of the Forest

Imagine a sweet tooth hidden in the dense undergrowth of forests, waiting for you to discover its delightful flavors. That’s what Hydnum repandum, also known as the sweet tooth or hedgehog mushroom, is all about.

The History and Description

This fascinating fungus was first described by Carl Linnaeus in 1753, making it a venerable member of the fungal kingdom. As the type species of the genus Hydnum, it’s like the golden retriever of mushrooms – always reliable and recognizable. The Hydnum repandum is a mycorrhizal fungus, meaning it has a symbiotic relationship with trees, helping them absorb nutrients in exchange for sugars produced by photosynthesis.

When you come across one, you’ll notice its distinctive yellow to light orange to brown cap, adorned with spines that hang down like tiny golden needles. The mushroom’s flesh is white and has a pleasant odor and taste – some say it’s spicy or bitter, while others find it sweet and nutty. When bruised, the tissue turns an orange hue, much like a sunset painting the sky.

Species Diversity and Distribution

The Hydnum repandum family is quite diverse, with molecular studies revealing that this species needs a revision due to poor overlap between morphological and molecular characteristics. A 2009 phylogenetic analysis showed two distinct clades, while a 2016 genetic study identified at least four species: southern China, Europe, eastern North America, and a reclassified H. repandum from Europe and northern China/Japan.

Interestingly, the genus has undergone intensive speciation, with one species (H. repandum) missing from Central America but with genetic material found in Venezuela. This shows how interconnected these fungi are across vast geographical regions, much like a network of underground rivers flowing beneath the earth’s surface.

Morphological and Chemical Characteristics

The specific epithet ‘repandum’ means “bent back,” referring to the wavy cap margin, while ‘album’ means “white as an egg.” This description paints a vivid picture of its appearance. The flesh of mature specimens is thick, white, firm, brittle, and bruises yellow-orange-brown, with a pale cream spore print. 5 by 4. 5–5. 5 μm. They usually contain a single, large refractive oil droplet.

The basidia (spore-bearing cells) are club-shaped, four-spored, and measure 30–45 by 6–10 μm. The cap cuticle is a trichodermium of narrow, club-shaped cells that are 2. 5–4 μm wide. Underneath this tissue is the subhymenial layer of interwoven hyphae measuring 10–20 μm in diameter. The spine tissue is made of narrow (2–5 μm diameter), thin-walled hyphae with clamp connections.

Chemically, both H. repandum and H. album contain diepoxide compound repandiol, which is under laboratory research. Volatile organic compounds responsible for the fruity aroma include eight-carbon derivatives like 1-octen-3-ol, (E)-2-octenol, and (E)-1,3-octadiene.

Similar Species

North American lookalikes are white hedgehog (Hydnum albidum) and giant hedgehog (H. albomagnum). H. albidum has a white to pale yellowish grey fruit body that bruises yellow to orange, while H. albomagnum is large and paler than H. repandum.

H. rufescens is smaller than Hydnum repandum, has a deeper apricot to orange color, and ellipsosporum spores that are 9-11 by 6-7.5 μm. These differences can help you distinguish between species when foraging in the wild.

Edibility and Culinary Uses

H. repandum is mycorrhizal, growing singly or in groups on ground or in leaf litter in coniferous and deciduous forests. It has fruit bodies with cap diameters 3-5 cm wide and is widely distributed in Europe, listed as vulnerable in some countries, and does not occur in Canada.

Dried H. repandum is 56% carbohydrates, 4% fat, and 20% protein, with high content of copper, manganese, palmitate, stearic acid, oleic acid, linoleic acid, and linolenic acid. It’s considered edible, sweet, nutty, and crunchy, similar to chanterelle mushrooms.

Repandum mushrooms can be cooked by pickling, simmering in milk or stock, and sautéeing to achieve a tender texture and mild flavor. The firm texture makes it suitable for freezing. Its natural flavor is similar to watercress or oysters, but older specimens may have a bitter taste that can be removed by boiling.

Some species are found under conifers and have an unpleasant strong taste. The form amarum is inedible due to its bitter fruit body. Repandum mushrooms are sold in Europe as pied-de-mouton and used as food by red squirrels, adding another layer of intrigue to their culinary history.

Conclusion

Hydnum repandum, with its sweet tooth hidden in the forest, is a fascinating species that continues to captivate mycologists and foragers alike. Its diverse forms and unique characteristics make it a true gem among mushrooms. So next time you venture into the woods, keep an eye out for this delightful fungus – who knows, you might just find your own sweet tooth in nature!