Boletes look like regular gilled mushrooms in that they have a cap and a stem, but they have a soft fleshy pore surface under their cap instead of gills. The pore layer is easily separated from the flesh of the cap, and the whole mushroom will feel soft enough to easily chew. Unrelated polypore mushrooms (and others) may have a pore surface, but they are usually tougher - at least as tough as leather if not as hard as a chunk of wood, and the pores cannot usually be easily removed from the rest of the mushroom. Boletes usually grow out of the ground, while polypores more often grow out of the sides of trees without stems, or are simply a pored surface lying flat without a cap on a piece of wood, but occasionally they will have a stem too.
Most boletes are mycorrhizal. Their spores are often three times or so longer than they are wide.
Like most non-gilled mushrooms, boletes are generally safer to eat and easier to identify than gilled mushrooms, although there are important exceptions. Gilled mushrooms have the greatest diversity and for whatever reason, more toxic species. In fact, some of the most desired edibles are boletes, in particular the porcini or king bolete (the Boletus edulis group).
Poisonous boletes are rare in the PNW. The most reliable reports of severe bolete poisonings come from some of those with red pores, the Rubroboletus. There are some quite common boletes that taste very bitter or very hot. These have been reported poisonous, because people eating them sometimes get sick, but I don't know if that's because of the unpleasant taste or if they're actually poisonous. Sometimes pleasant tasting species can cause gastrointestinal distress in some people, for instance, the red capped Leccinum.
Key to Boletes: (the larger ones may grow to >20cm)
There are many different kinds of boletes. We don't have very many of them in the PNW compared to other parts of the world like the east coast, where it is joked that they have more genera than we do species. You should be grateful you don't have to learn them. Boletus is the Latin genus that most people think of when they think of the word bolete (as you might guess because the words are very close), but Boletus (capitalized) is just one kind of bolete (not capitalized). Many yummy species are here.
The king boletes: once the DNA work is complete, it is likely that these are going to be the only species still called Boletus. Everything else will get new genera. Mushrooms in this main group are often called the porcini or ceps. They can be huge (up to 30cm) and are highly prized. There are many species in this complex, all equally tasty.
All have a net-like reticulation pattern on the top of a (usually) bulbous stem. Pore surface white when young, yellow when mature. They do not usually turn blue, but sometimes slightly so.
B. edulis var. edulis - "King", brown cap, whitish young pores (most others are yellowish) and bulbous stem.
B. edulis var. grandedulis - even larger with darker, reddish cap tones, brown tubes when mature and a darker stem.
B. regineus ('aereus'/
Butyriboletus - the butter boletes: like the king boletes with reticulated stems and often bulbous stem bases, but with yellow pores, stem and flesh that often turn blue. Large and stocky (10-15cm or so). They get rarer the further north you travel from California. Reports of the European species B. appendiculatus (not pink) and B. regius (pink) are actually the following species:
Caloboletus - the bitter boletes: May be huge (20-30cm), very common. Mistake these for porcini and you'll wonder what all the fuss is about, but these all blue, and don't usually have the bulbous stem often seen in B. edulis. Not to mention that they are usually horribly bitter.
C. frustosus (C. conifericola/
Chalciporus - smaller (<10cm), hot and peppery, yellow to brown pored boletes. Yellow mycelium at the stem base. Perhaps they are parasitic on Amanita muscaria, but it's hard to tell if they are restricted to growing near that Amanita since that grows almost everywhere.
Porphyrellus - a distinctive dark, greyish-black pored bolete. East and south of here are other similar species, but in the PNW so far, it's unique. When young the pores might be whitish, but the rest of the mushroom is still dark. Blues, the blue quickly turning brown. 5-15cm.
Rubroboletus/Neoboletus/Suillellus - the red-pored boletes, some of which can be quite poisonous (Rubroboletus). All are rare, occuring more commonly south of here, and turn blue. Usually 10-20cm.
Rubroboletus eastwoodiae ('satanas') - red, reticulated and very bulbous stem. Under oak. Moderate bluing. Poisonous.
Rubroboletus pulcherrimus - clavate, not bulbous, reticulated species. Red-brown cap and stem. Poisonous.
Rubroboletus haematinus - yellow pores only turning red in age, except at the margin, so watch out! Otherwise similar clavate, reticulated species with a yellow stem and usually paler brown cap. Poisonous.
Aureoboletus/Buchwaldoboletus/Pulveroboletus - some distinctive species, with odd characters not usually seen in 'Boletus'... a viscid cap, partial veil, eccentric stem or overhanging cap margin. Often brilliant yellow.
Aureoboletus flaviporus - unusual viscid cap and extremely vivid yellow pores. Hardwoods, especially madrone.
Buchwaldoboletus lignicola - eccentric stem, often growing on wood, possible overhanging cap margin and large pores. Stains blue when bruised.
Red Stems (but not red pores) and a mild taste. Pulchroboletus, Xerocomellus and Hortiboletus, usually not reticulated. Usually small-medium (<10cm). Bluing
First, let's rule out the two small genera.
'Pulchroboletus?' (Boletus) smithii - the top of the stem is red (unlike B. rubripes), and the brownish yellow cap becomes more red as you rub it. Blues. P. vividus and P. amyloideus are related gastroids.
Hortiboletus 'rubellus' - Deep red cap and stem contrasted with bright yellow pores and stem top. May blue. Similar to Xerocomellus dryophilus.
Xerocomellus - many species, hard to tell apart
Xerocomellus diffractus ('chrysenteron') - cracked cap, perhaps with pink in the cracks. Reddish stem. Blues slowly.
Xerocomellus amylosporus - very similar, darker cap with irregular cracks, staining inky blue, stem stains dingy brown.
Xerocomellus mendocinensis ('truncatus') - very red stem, darker cap, less cracking (may resemble X. zelleri), but bluing quickly.
Xerocomellus zelleri - Beautiful black cap contrasted with yellow pores and red stem. Some may blue slightly. Slightly velvety but not very bumpy cap, with a pale rim. Slender.
Xerocomellus rainisiae (rainisii/
Xerocomellus salicicola - pink cap when young, red stem apex with some reticulation, cracking. Hardwoods.
Others - none of the above, including Xerocomus, Hemileccinum and Gyroporus.
'Boletus' mirabilis - very velvety cap with a dark stem streaked like a tree trunk (compare B. fibrillosus) but has yellow pores and grows on wood. It tastes of butter and lemon! Rarely blues. Up to 15cm or more.
Xerocomus 'subtomentosus' grp
- three species, including X. oregonensis ('ferrugineus'/
Hemileccinum subglabripes - yellow pored, almost like a Leccinum with scabers that do not develop very visibly. Does not blue.
Gyroporus borealis ('castaneus') - a rare and interesting small (5cm or so) east coast bolete that has been introduced under landscaped hardwoods. It has hollow chambers in the stem and almost looks like it has notched or free white pores, a concept normally only used for gilled mushrooms. Does not blue.
Leccinum: the scaber-stalked boletes, not to be
confused with Suillus which has glandular dots that look painted on compared to
scabers that can be removed. These are edible, although some people report
allergic reactions to the red capped ones (which stain blue/
Leccinum were well studied back in the 60's, but we still know little about them since we don't have DNA or colour photos of most species. Names is single 'quotes' are European species that have not yet been proven to be here. The other species are described from North America but do not make up a complete list and may not represent a one-to-one mapping to the species that occur here. The upshot is you can't really trust the names you see on our local Leccinum yet (nor probably on these photos).
L. scabrum/schistophilum - the birch boletes, often found with urban birch. Dark brown cap.
L. rotundifoliae - similar alpine birch species.
L. brunneum - dark brown capped aspen bolete. Idaho.
L. 'holopus' - a pale birch bolete with a whitish cap. May stain red.
L. 'cyaneobasileucum' - brown birch species with bluing in the stem base may indicate this species?
L. clavatum - an albino conifer Leccinum with a thick, clavate stem. Stains blue-grey. Large. Idaho.
The smooth orange-red capped group is confusing and not well studied yet, but here is what others have said so far. Note that only one group has black scabers when young, the rest darken in age, possibly to black. I doubt these species concepts will hold up to DNA scrutiny. If I was a betting man, I'd bet that the species you find might have most to do with what trees are nearby.
Suillus - The Slippery Jacks, considered inferior edibles to most of the other genera, although some are said to be good. Suillus is suggested by a sticky cap instead of a dry one, or a veil, or glandular dots on the stem (but often all three). Suillus tomentosus has no veil and sometimes a dry cap, and therefore is probably the most difficult one to recognize to genus. Many of them have a preference for pine trees. The glandular dots are simply coloured spots that look painted on, unlike the scabers of Leccinum which can be removed. Some of them may stain somewhat blue in the pores or flesh when handled or exposed to oxygen, while others turn brownish. 5-10cm or more unless otherwise specified.
Let's start with the ones that do not have a veil. It can be tricky to tell... often the veil might rub off in old age so it's easiest to tell on a young specimen, but if you look carefully you can usually tell because there will be some kind of clue or remnant left around the stem or cap margin. It just takes practice to know what to look for. These do not blue, except for S. tomentosus.
Suillus brevipes - dark cap (rarely pale), no dots on the stem (thus a clean look), often a short stem, under 2-3 needle pine.
S. subalpinus ('granulatus'/
S. tomentosus - rough, almost dry cap and no ring, orange colours, including in the pores. Slowly blues. 2-needle pine.
Rough-capped Suillus: These do not appear very Suillus-like because the caps are not very sticky, in fact they are pretty rough and scaly, but they do have an obvious veil. Some exhibit a slight bluing: S. lakei in the base of the stem and S. ochraceoroseus throughout.
S. lakei (flavogranulatus?) - a pinkish brown distinctively scaly cap with large pores that stain brown. One version is very much like S. caerulescens with subtle scales. Douglas fir.
S. ampliporus ('cavipes') - dark brown with large pores. Easily recognized by its hollow stem. Larch.
Next, species with glandular dots on the stem (they do not blue). First, with a weak partial veil, that usually does not stay on the stem to form a ring, you may only see some remnants along the edge of the cap.
S. brunnescens (borealis) - young white cap and stem staining chocolate brown, weak purple- to red-brown veil, with stem dots. 5-needle pine. Closely related to S. luteus.
S. americanus (sibiricus) - a very yellow Suillus with reddish-brown patches near the cap margin. Sometimes with large pores. Glandular dots. 5-needle pine.
These species with glandular dots usually do have a conspicuous ring on the stem (they also don't blue).
S. luteus - the Slippery Jack itself. Dark cap colour and purple sheathing veil (splays up). Lots of glandular dots. S. brunnescens can sometimes look similar. 2-needle pine.
Finally, the sometimes difficult to recognize species without conspicuous glandular dots on the stem (there may be a few). The ring may or may not be conspicuous.
S. caerulescens (imitatus var. imitatus) - streaky yellow brown cap. Pores bruise brown and only the bottom of the stem bruises blue. Suillus lakei can look very similar with sometimes subtle scales. Douglas fir.
S. ponderosus (imitatus var. viridescens) - a little darker brown than S. caerulescens, occasional green patches, often bigger and stockier, with yellow-orange slime on the veil when young. Douglas fir.
S. clintonianus (S. grevillei var. clintonianus) - usually chestnut coloured with a yellow rim and a yellow to chestnut veil, but harder to recognize when the colours fade. Also staining brown, but sometimes blue in the stem base. Larch.
S. elbensis ('viscidus'/
S. flavidus (umbonatus/
S. albivelatus - white veil, like many others, not bluing but parts tend to stain pale vinaceous. Little veil material on the stem. 2-3 needle pine.
Congratulations! You are now familiar with an entire group of mushrooms that contains many good edibles, all of our fleshy pored mushrooms. For specialized literature, please see North American Boletes by the Bessettes et. al.