Genus Hydnoporia Murrill

Summary: Three species of Hydnoporia are known for North America so far. All three can form glue crusts. One is new for eastern states. The name H. corrugata applies to that species in Europe. Some previous synonyms of H. corrugata apply to H. olivacea instead.

Taxon Comparisons

1. Hydnoporia olivacea (Schwein.) Teixeira 1986

   Toothed Oak Crust is an olive-brown crust on dead fallen hardwood branches. It is common in oak woodlands around the Chicago Region, and elsewhere in North America. The hymenium is irpicoid meaning the underside is toothy-poroid, as seen in the whitish Irpex, where the teeth are flattened and irregular. A hand lens may reveal the projecting setae (spines).

   See the Miettinen et al. (2019) paper on H. olivacea, H. diffisa, and the European H. corrugata. Some synonyms of H. corrugata, including H. agglutinans, are now thought to be synonyms of H. olivacea. This implies that glue crust collections in America represent multiple species of Hydnoporia.

   The Gary Lincoff photo here of his glue crust shows an adjacent brown toothy hymenium, matching H. olivacea. Compare to the Tom Bigelow photo showing a gray cracked hymenium and blackish glue.

   On north side of Chicago in 2023, we found an example of Hydnoporia olivacea gluing branches together with brown mycelium.

   

   

   

2. Hydnoporia diffisa Spirin & Miettinen 2019

   This species, named for the cracking hymenium, is recently published. See Miettinen et al. (2019): the hymenium is grayish, later pale chocolate brown. When mature it is strongly cracked, and the margin becomes ferruginous brown (darker than hymenium). The poorly visible subiculum (the bottom layer underneath attached to substrate) is dark brown to blackish. Sterile patches are small and bright ferruginous brown. H. diffisa is described from eastern United States, North Carolina, New York, and present in Colombia and Peru. It is an American relative of the European Hydnoporia corrugata, which also has cracking (syn. Hymenochaete corrugata).

   I have an alder glue crust specimen from northern Wisconsin. It has blackish glue but no obvious hymenium. Microscopic characters may help identify it.

   

   

3. Hydnoporia tabacina (Sowerby) Spirin, Miettinen & K.H. Larss. 2019

   Named for its tobacco color, this effused-reflexed crust has a smooth underside with projecting setae (spines) visible with a hand lens. There are a few records in the Midwest but none yet near Chicago. It is circumglobal in the northern hemisphere (Holarctic) but more research may determine if the American and Asian material is separate from that of Europe, where it is called Willow Glue.

   Compare this carefully to similar species of Hymenochaete, such as H. rubiginosa, but also Punctularia strigosozonata (Gary's Tree Bacon).

   

   

Taxon Information

This Murrill genus Hydnoporia was resurrected to replace Hymenochaetopsis (itself a replacement name for Pseudochaete). It contains species, previously part of Hymenochaete and other genera, found to be in a more distant clade. Most species are found on hardwoods. Some may initially be parasites on the woody plants and spread between host shrubs or trees when adjacent branches touch. The mycelium bridges the gap and binds the branches together, giving them the name of glue crusts. This is a very cool method for the fungus pathogen to spread from one host to another one, killing branches in the process. I find it puzzling that this behavior is not mentioned or discussed in recent taxonomic papers. The aerial mycelial transfer is described by Ainsworth and Rayner (1990).

See the Miettinen et al. (2019) paper; a free PDF is available at link below. Analysis of ITS and nrDNA tef1 sequences along with morphological and biogeographic data sorted out most of the species. Lectotypes were designated where needed to stabilize names. The synonymy in this group was investigated. Notably some names of glue crusts previously assigned as synonyms to H. corrugata, including H. agglutinans, are now thought to be synonyms of H. olivacea. So, take note, a crust fungus gluing branches together cannot be assumed to be H. corrugata. Our other species of Hydnoporia have this ability.

Species

There are fourteen accepted species listed formally by Miettinen et al. (2019) with new combinations into Hydnoporia. They estimate there are 20 or more species (northern hemisphere).

• Hydnoporia corrugata, Europe.
• Hydnoporia diffissa, eastern North America, Colombia, Peru.
• Hydnoporia gigasetosa, India, China.
• Hydnoporia lamellata, East Asia.
• Hydnoporia laricicola, Russia, Asia.
• Hydnoporia latesetosa, tropical China.
• Hydnoporia lenta, Costa Rica.
• Hydnoporia olivacea, North America.
• Hydnoporia rhododendri, Europe, Asia.
• Hydnoporia rimosa, East Asia.
• Hydnoporia subrigidula, China.
• Hydnoporia tabacina, circumglobal, Northern Hemisphere.
• Hydnoporia tabacinoides, Japan.
• Hydnoporia yasudai, East Asia.