Updated: Mar 29, 2020
I would hazard at guess that this may be the most commonly recognized edible wild mushroom in the Southern Rocky Mountains. It goes by many names: porcini, king bolete or 'king', Rocky Mountain red-capped bolete, Rocky Mountain red, penny bun, or often just simply 'bolete'. You may also see people mistakenly refer to this mushroom as B. edulis because it was actually classified as B. edulis until 2014 when David Arora and Jonathan Frank published a paper that distinguished our Rocky Mountain porcini as it's own species! (https://www.pnwfungi.org/index.php/pnwfungi/article/view/1267)
This species holds a special place in my heart! When I started mushroom hunting around age 10 this was the first species that we looked for; my introduction to the world of fungi.
This is a great mushroom for beginners to learn because they're often plentiful and easy to find, they're simple to identify if you follow a couple rules, and they're delicious! In the rest of this post we will go over the main characteristics of the Rocky Mountain red, where and when to look for them, common look-a-likes and the traits that differentiate them, and anything else that I think you should know about this species!
Boletus rubriceps is a stout mushroom with convex cap that is reddish brown in color and often slightly sticky or "greasy" when fresh. It has a robust stem, pale cream to white in color with white or sometimes light pinkish reticulations (net-shaped patterns). The spore-bearing structures are sponge-like pores. They are white in young specimens but progress to yellow and eventually greenish brown as the mushroom matures. The flesh is white and does not stain when cut, though it can be accidentally stained during cutting by pulling some of the cap or pore color through with the knife.
These mushrooms usually begin fruiting with the summer rains in July (if we get them...) and can be found into late September or October. Early in the fruiting season they can be found as low as 8,000 ft and will continue to fruit up in elevation all the way to the treeline. In Colorado they mainly associate with Engelmann spruce (Picea engelmannii), and sometimes firs (Abies spp.) and Douglas fir (Pseudotsuga menziesii). They can also be found in association with pines (Pinus spp.), but it is less common in my experience.
Now that we've gone over when they fruit, what trees to look out for, and which elevations to target, let's get more specific about where to look! I tend to focus my searches on northern aspects, these north facing slopes tend to stay a little cooler and hold moisture longer. This can be especially useful during the dry years that we often have in Colorado! Porcini can often be found fruiting along trails or near creeks or other water holding features, though I do tend to find them a little further away from the moisture than some species. While looking for B. rubriceps you should also look out for fly agaric mushrooms (Amanita muscaria), and hawk wings or scaly hedgehogs (Sarcodon imbricatus), as these species share environmental preferences with them.
Boletus rubriceps has very few look-a-likes, and the few that it might be confused with are very easy to tell apart once you learn some key traits. The most commonly mis-identified species are from the genus Leccinum, also known as 'scaber stalks'. At first, these mushrooms can definitely appear to be B. rubriceps, however upon closer examination a few obvious characteristics will give them away. The first is how the genus Leccinum gets its common name, the presence of black or brown 'scabers' on the stalk. The word 'scaber' comes from scabrous meaning rough or scab-like, but the 'scabers' are actually fairly soft, feeling almost like the mushroom has fur on it stalk. The next very obvious trait, if you miss the scabers, is staining flesh. The species we have in Colorado can stain blue, purple, grey, or even reddish, though the first two are most common.
It's worth noting that many people consider the Leccinum species we get in Colorado to be edible. However, most field guides, as well as myself, advise caution. There have been many instances of poisonings concurring from orange capped Leccinum, often referred to as 'aspen boletes'. There has not been any definitive answers as to why the poisonings are occurring, but the symptoms sound bad enough that I personally choose to leave these mushrooms in the forests.
The other mushrooms that I sometimes see confused with Boletus rubriceps are from the genus Suillus. The mushrooms found in this genus are also easily differentiated with a few traits. The first is simply shape and size. Suillus species in Colorado are usually pretty small, rarely having caps over 5 inches or so. Their stems are skinny and small compared to the stout stem of a porcini, and they also have a unique trait called 'glandular dots'. These are little dots that spread down the stem starting at the cap, they're often brown or tan in color, but sometimes light or even white. The other obvious feature of mushrooms in the Suillus genus is a very sticky cap. These mushrooms will often have pine needles and dirt stuck to their caps! That said, in dry conditions this stickiness can sometimes be very faint or completely missing in some specimens. From there traits can vary between species, some will stain when cut or damaged, some can have residual rings from a partial veil, some can even have a velvety appearance to their caps. Don't get overwhelmed though, differentiating between these is fool-proof as long as you know the traits of Boletus rubriceps and the above traits from Suillus!
Finally, a few notes about harvesting porcini once you find some! Many people will suggest cutting wild mushrooms to preserve mycelium health, we will save that discussion for another day, but here is a link if you'd like to do some more research on the topic: http://www.fungimag.com/spring-2012-articles/LR_Agaricidal.pdf
I would recommend a gentle pulling and twisting motion to harvest them. These mushrooms often are surrounded by dirt and organic material, especially when young, and it makes it very hard to get a knife in for cutting them cleanly. Pulling also results in more mushroom to take home! Once removed from the earth, simple brush and cut away any debris without wasting too much meat.
These mushrooms, and many others, will often house small fly larvae once they've matured a bit. If you start to clean one and find a lot of small holes or larva just put the mushroom back where you picked it or break it into pieces and disperse it around the around the area. This is a personal decision, some people don't mind the "extra protein", I usually take specimens with a few holes, but any with lots of larva get lefts behind.
Lastly, as mentioned above, once these mushrooms begin to mature their pores become yellow or even greenish-brown. I will leave the pores on young porcini if they are still white or off-white and consume them with the mushrooms, but once they become yellow I remove them and spread them around the area before leaving. I personally find that they can become bitter at this point, though many people keep them and enjoy the flavor, or they separate and dry them to use as a mushroom powder or thickening agent!
Although this year (2018) is looking like it may be a tough one for much of the state in regards to summer rain, I would still recommend that you get out and look! Focus on micro-climates near streams or other water holding features. If there is any moisture these mushrooms will fruit. Plus, there's never a bad day spent in the woods!
As always, don't hesitate to reach out with comments or questions! I would love to hear what you think about the Forage Weekly series and if you have any requests for species to feature in a future post!