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Alder RollrimPaxillus rubicundulus
Kingdom: Fungi
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| Common name | Alder Rollrim |
| Scientific name | Paxillus rubicundulus |
| AKA | Alder Roll-Rim, Red-Brown Rollrim |
| Season (UK) | Late summer to autumn (typically August to November) |
| Habitat | Wet woodland and waterside - exclusively associated with alder (Alnus glutinosa) |
| Cap diameter | 3cm to 10cm |
| Spore print | Rusty brown (useful for ID) |
| Edibility | POISONOUS!! do not eat under any circumstances! |
| Rarity | Uncommon to scarce |
The Paxillus genus contains a group known collectively as the 'Rollrims' which are named for the distinctively inrolled cap margin that all species share. They often have the look of something that should be edible (boletes, chanterelles, decent honest mushrooms). They are not. The family resemblance is there, but the Alder Rollrim is mean.
Overview
We've actually seen this one in the wild, which puts it one ahead of a lot of the mushrooms we’re covering in our efforts here (low bar, we know, we will do better). At least, we probably saw it - there’s an alder-populated space in Childwall (appropriately called Childwall Woods and Fields, which was planted back in the 18th Century by rich locals) and, in the sort of damp woodland that would enter pretty low on anyone's foraging destination list, we’re reasonably sure we spotted this mushroom - it just looked like several different things at once, and we’re pretty rubbish at ID, so it could have been a bolete but, from another angle, possibly something chanterelle-adjacent, or something you'd maybe describe to a friend as 'a medium-sized concern-for-safety' if it was growing in your direction. We’re ticking it off our list anyway. You can’t stop us.
Paxillus rubicundulus is considered in the general literature as an uncommon to scarce fungus across Britain and Ireland, almost exclusively in wet habitats alongside common alder (Alnus glutinosa - the one with the little cone-like catkins, you'd know it if you saw it). Stream banks, pond edges, boggy bits, that kind of thing. It's a specialist in a way most woodland fungi aren't, forming ectomycorrhizal partnerships with alder specifically, which makes the habitat almost more useful for identification than the mushroom itself. No alder, no Rollrim. Simple. Unless you’re as bad as we are, then it could have been anything.
From people who know this stuff, we can say the cap is rust to reddish-brown, the gills run down the stem and bruise darker when handled, and that the whole thing has a slightly sticky quality in wet weather. Honestly, it’s not even trying. From pictures, the rolled margin gives it a slightly sulky expression (aesthetically, a three at best, but it definitely looks like it wants to ruin your afternoon).
There is no gift shop version of the Alder Rollrim. We've checked. In the dialect of the area we found them - they proper ming. The Rollrim family has a reputation that precedes it, and for excellent reason (we'll get to it in the edibility section).
Do Not Eat: All Rollrim species should be treated as poisonous regardless of appearance or confidence level. Wild Food UK, one of our favourite sources, is clear: after molecular studies divided the genus into multiple species, the entire Paxillus family is off the table (badumtish). The bruising gills are a useful identification signal.
Identification
Young specimens can look almost appetising (don't, like, really - don’t). The cap starts convex, flattens to a broad funnel as it matures, and the colour ranges from pale ochre-rust through reddish-brown to a sort of tired yellowish-brown that mycology books describe as 'fulvous', which is just showing off. It could as easily be described as 'the colour of a ginger biscuit' which would be enough to convince many people it shouldn’t be eaten.
Its surface is smooth to finely scaly, sticky in wet weather, the margin of the cap is strongly inrolled, especially in younger specimens (that rolled-under rim that gives it its name is the family's most consistent feature and your first identification flag).
The gills are crowded, pale yellowish-brown to ochre, and run down the stem (decurrent). The critical detail: they bruise. Handle them, damage them, press them with a finger, and they darken (sometimes to a wine-red colour, sometimes to rust-brown). That colour change is one of the most reliable signals in the whole Paxillus genus. If the gills are going brown, put it down, as Flanders may have said.
The stem is stout, solid, and typically paler than the cap. Relatively short for the cap size, sometimes slightly off-centre, with a faintly compressed look in older specimens that adds to the general sense that this mushroom has had a difficult week.
The spore print of the alder rollrim is rusty brown - a warm, distinctly reddish-brown rather than the more yellowy-brown of some superficially similar species. Worth doing, if only to confirm what you already strongly suspect (or if you want to be able to say you’ve definitely seen it rather than just holding tightly to a suspicion.
Best single ID rule: no alder, no Alder Rollrim. Check the tree first.
Lookalikes & ‘Mix-Up’ Species
Do Not Eat: No, seriously, put it down. The chanterelle confusion is the one to take most seriously. Young, pale Rollrim specimens in damp conditions have caught out experienced foragers. The key check: chanterelles have forked, blunt-edged ridges (not true gills), don't bruise, and smell faintly fruity. The Rollrim has crowded, true gills that bruise darker when touched.
This is the section that justifies a Mushipedia entry for something you should never eat and which, honestly, we’re never going to stick on a hat. The alder rollrim is genuinely useful to know about because at various stages of development it resembles several things you would very much want to eat, and the consequences of confusion are, as we'll explain shortly, not small.
Chanterelle (Cantharellus cibarius) — young, pale, funnel-shaped Rollrim specimens are the problem here. Similar colour range, similar habitat, similar approximate size. The differences (blunt forked ridges vs true gills, the bruising, the fruity smell vs the Rollrim's faintly earthy-sour one) are clear on close inspection. The issue is that 'close inspection' requires knowing what you're inspecting for, which we absolutely don’t and is precisely what this entry is trying to provide with help from people who do.
Penny Bun / Cep (Boletus edulis) — the bolete resemblance comes from the Rollrim's taxonomic identity as much as its appearance: Paxillaceae sits within the order Boletales, meaning it's genuinely more closely related to boletes than to typical gilled mushrooms. The gills can appear almost pore-like near the stem in some specimens, but a proper bolete has actual pores — run your finger under the cap and you'll know immediately (one is a sponge, the other has distinct gills). Takes two seconds and a healthy amount of alcohol hand cleaner stuff.
Brown Rollrim (Paxillus involutus) — the more common, more studied, and historically more deadly close relative. Also poisonous. Associates with birch and other hardwoods rather than alder. Larger, more robust, less reddish. If you're near alder and water, rubicundulus is more likely; dry birch woodland suggests involutus. Leave both of them alone.
Paxillus olivellus - a closely related species, formally described in 2016 by French mycologist Pierre-Arthur Moreau and colleagues, which has since been found to be widespread in Britain and was historically lumped in with rubicundulus. Also associated with alder. Also poisonous. The Paxillus genus is extremely committed to the bit. Maybe we saw this one. We’ll literally never know.
Edibility
Did We Mention “Do Not Eat!”: If you believe you or someone else has eaten a Rollrim species, seek medical attention immediately and do not wait for symptoms. The mechanism is cumulative and the onset of serious symptoms can be delayed. Take a sample of the mushroom with you if at all possible.
No.
Just no.
No arguing, you understand? No.
The longer version?
The Paxillus genus contains toxins that work through a mechanism that is, frankly, more alarming than most. They sensitise the immune system over repeated exposures — meaning the first few times they’re eaten (and yes, people did eat them, for years, in parts of Eastern Europe particularly, where involutus was considered edible well into the 20th century), you might feel nothing. Or mild gastrointestinal unpleasantness. The problem is that each exposure builds sensitisation and, at some unpredictable point, the next meal triggers haemolysis - the destruction of your own red blood cells by your own immune system, followed by kidney failure, circulatory collapse and, in documented cases, death. The mushroom doesn't poison you. It makes you poison yourself.
No antidote. Treatment is supportive only. This is a properly scary mush.
The case that changed the formal classification was Julius Schäffer, a German mycologist who died in October 1944 after eating a meal containing Paxillus involutus. He is, somewhat grimly, considered the only professional mycologist on record to have been killed by a fungus he was studying. The mushroom wasn't formally reclassified as being deadly poisonous until 1981 (thirty-seven years after it killed one of the people who studied it professionally, which seems slow to us). Mycological publishing moves at its own pace it seems.
For rubicundulus specifically, the toxicological picture is less thoroughly documented than for involutus as it's rarer, less studied, and the molecular work that confirmed it as a distinct species only happened in 2016. Wild Food UK's position is unambiguous: treat all Rollrims as poisonous. That seems like the right call.
Naming history
Paxillus rubicundulus was formally described in 1969 by Scottish mycologist Peter D. Orton, published in the Notes of the Royal Botanic Garden Edinburgh — a pleasingly grand provenance for a mushroom you'll find in a ditch by a canal. Orton was a prolific and meticulous describer of British fungi, which is a mad job description when you think about it, through the mid-20th century, responsible for distinguishing and naming a significant number of species that had previously been folded under broader European designations. Rubicundulus was part of a larger effort to untangle the alder-associated Paxillus species from the involutus complex. Well done that man.
The species name rubicundulus comes from the Latin rubicundus, 'ruddy' or 'red-faced' — a reference to the reddish-brown cap tones. It's a diminutive, so technically 'a bit ruddy'. That feels accurate. The genus name Paxillus, 'peg' or 'small stake' (a reference to the stipe shape), was established by Elias Magnus Fries in 1821, the same Swedish botanist who formalised much of modern fungal taxonomy, and whose authority was so widely deferred to in 19th-century mycology that the abbreviation 'Fr.' appears after more species names than anyone else's. Taxonomy has its celebrities.
For decades, rubicundulus was treated as a synonym of Paxillus filamentosus (since formally rejected) and was only properly separated after molecular phylogenetic studies in 2016 confirmed it as part of a species complex containing at least three distinct taxa - which is way more common than you’d think. Two of those species, Paxillus olivellus and Paxillus adelphus, were described as new to science that year. Which means there's a reasonable chance that what you find beside a British alder isn't technically rubicundulus at all (by you, we mean we, we’re increasingly convinced as we research). Whether that affects your decision about eating it is a question with an obvious answer. Do not eat the mushroom.
Ecology
The Alder Rollrim is a genuine specialist — ectomycorrhizal, and almost exclusively partnered with common alder (Alnus glutinosa) in wet, riparian (that, which our American friends may call a ‘ten dollar word’, means ‘situated on a riverbank’) habitats. The habitat specificity is unusual in the Paxillus genus, where involutus and its relatives are considerably more flexible in their tree partnerships, and it means the alder rollrim's distribution maps almost directly onto the distribution of mature alder in wet lowland habitats. Find one, you've effectively found the other.
There's a broader (and genuinely fascinating) question here about the evolutionary timeline of the Paxillaceae. The family's estimated divergence date of around 98Mn years ago places its origins in the same era as the angiosperm radiation, the explosive spread of flowering trees that transformed terrestrial ecosystems in the Cretaceous.
Whether the family's various tree partnerships (alder for rubicundulus and its relatives, birch and others for involutus) represent ancestral traits or later specialisations is the kind of question that produces long papers and strong opinions in mycological circles. Not really what we're here for today, but worth mentioning because it's actually pretty cool that that thing in the ditch probably killed a dinosaur.
Common alder is, itself, interesting in this context: it's one of very few broadleaved species capable of fixing atmospheric nitrogen via bacterial root nodules, making alder woodland unusually fertile. Whether the Rollrim benefits from this directly, or simply colonises alder habitat because alder is common in the wet lowland sites it prefers, isn't clearly established. Probably both, though, right? We can’t stress enough, we don’t know and are absolutely not the people to ask.
Where to Find It in the UK
We found it, possibly, in a woodland in a populated suburb of south Liverpool, which probably isn't the romantic foraging narrative you'd hoped for, but there it was, maybe, looking like something that wanted to be a chanterelle when it grew up, but probably wasn’t being raised right. We did not eat it. We lived. A successful outing by any reasonable measure.
Uncommon to scarce is the - this isn't a species you'll stumble across every autumn. The habitat requirement is specific enough that you're essentially looking for it beside alder-lined water anywhere in Britain. Canal towpaths are apparently underrated for this (and for fungi in general), so maybe a trip to the Venice of the UK (Birmingham, in case you don’t know this particular fact) should be on every budding mycophile’s bucket-list - but don’t eat it, it shouldn’t become a kick-the-bucket-list.
In England, the river valleys and Fens of East Anglia provide classic alder carr habitat, as do the Somerset Levels and the Thames valley. The New Forest also has wet valley bogs with established alder populations while, further north, the valley bottoms of the Yorkshire Dales and Lake District (particularly along becks where mature alder overhang the water) are worth checking. If anyone lives near Childwall, go take a look and let us know if we’re talking rubbish.
Wales also offers good riparian (yeah, twice in a single page, baby) habitat throughout — the Wye Valley, and the river valleys of Powys and Ceredigion where alder lines the streams through hill country.
Scotland's river systems, particularly in Perthshire and Argyll, also have extensive water adjacent (we couldn’t use it a third time in such quick succession) alder woodland, and are probably under-recorded for this species.
The NBN Atlas records for rubicundulus specifically are sparse (partly because it's genuinely uncommon, and partly because the 2016 molecular work that clarified the species complex means older records may have been filed under Paxillus filamentosus, or simply as Brown Rollrim). The real distribution is probably better than the map suggests, but - as ever - who are we?
Discovery season runs roughly August to November, with September and October apparently the most productive. Look after rain (like, following rain, we’re not asking you to adopt wet weather), low to the ground, in leaf litter at the base of alder trunks or among surface roots. If the tree isn't alder, keep walking.
Worth knowing
Paxillus involutus was listed as edible in at least one widely-distributed Italian field guide as late as 1998. That's thirty-seven years after Julius Schäffer's death, seventeen years after the official reclassification, and roughly 98 million years longer than it should have been, we may have saved many dino-lives. Mycological publishing, as a field, has improved considerably over the last hundred years, however, we're just noting this for accuracy, not to alarm anyone.
The antigen responsible for the autoimmune response in Paxillus poisoning has still not been fully identified. We know it's heat-stable (cooking does nothing), we know it builds sensitisation over repeated exposure, and we know the results can be fatal. We don't know exactly what it is. That feels like unfinished business of some importance and also like something that should 100% have appeared in an episode of House.
Julius Schäffer, the mycologist killed by involutus in 1944, had been studying the genus professionally for years. He knew what it was. The current understanding is that he'd eaten it before without serious consequence and simply (at that particular meal, at that point in the sensitisation process) ran out of road. Sneaky mushroom.
We put this mushroom in Mushipedia not because it's beautiful or rare or gastronomically interesting (it is none of these things), but because the lookalike risk is real and the consequences are serious, and we’re going to try and cover all of the UK species in this manner. However, the more people who can confidently identify it and walk past it, the better.
Sources: Wild Food UK, The Wildlife Trusts, First Nature, Woodland Trust, Jargeat et al., Fungal Biology (2016)
This article is for informational purposes only. The Alder Rollrim is poisonous and should not be consumed under any circumstances. If you believe you have eaten a Rollrim species, seek medical attention immediately — do not wait for symptoms. Mushroom Future cannot be held responsible for foraging decisions made on the basis of this or any other written guide. Especially the bit about the canal towpath.