Observation 102691: Boletus bicolor Peck
When: 2012-07-22
No herbarium specimen

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Bicolor group
By: walt sturgeon (Mycowalt)
2012-07-31 13:59:19 BST (+0100)

Ammonia on the flesh of B. sensibilis is quickly yellow. On the flesh of B. bicolor it is negative. But chemical tests can be misleading especially on the cap cuticle where testing certain areas of th cap produces different reactions.
Xanthoconium separans shows different reactions on the lilac areas. Also the age of the specimen can make a differece. Two field charachters I use are that B. sensibilis has the sweet odor of fenugrek, maple syrup etc. and B. bicolor does not. Also the tubes of B. bicolor are extremely short in relation to the flesh. The slower and less strong blue bruising of the flesh is also typical of B. bicolor. There are other lookalikes such as B. bicoloroides, B. carminipes and B. miniatoolivaceus. At last year’s NAMA Foray there was considerable debate about these yellow pored ruddy capped boletes. They are not easy!

KOH test on cap?
By: John S. Harper (jsharper)
2012-07-30 20:04:10 BST (+0100)

Walt – I was at the West Virginia Mushroom Club foray this weekend near Davis WV. There were boletes on the table that Gary Lincoff and Bill Roody apparently agreed were B bicolor (var bicolor?). In my clubs (MAW) we always worry about whether these are B sensibilis instead.

I collected some very (to me indistinquishably) similar specimens to what was on the table and tested at home with KOH last night. The reaction was clearly relatively prompt olive-yellow color on the red brick cap. In my books that is noted as the expected reaction for B sensibilis, rather than B bicolor. Do the specimens that you collected show any KOH reaction on the cap? [KOH on the context did not do much – maybe made it a little bit darker yellow, but it could just be the moisture].

The other distinguishing feature between these two species that I have learned is to note the rapidity with which the yellow context turns blue. Rapid for sensibilis and slow (or not at all) on bicolor. (Both stain blue on pore surface when bruised, but in this case, I think also slower for bicolor.) My specimens have slow and not very strong blue staining – mostly on the context nearer the pores.

Any other suggestions of what you look for to decide you really have a bicolor in hand?

I may post an observation with some photos if it seems worthwhile.

Created: 2012-07-25 03:17:35 BST (+0100)
Last modified: 2012-07-25 03:17:37 BST (+0100)
Viewed: 62 times, last viewed: 2016-09-07 10:25:23 BST (+0100)
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