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A Bolete close and possibly associated with oak trees - Case 1

  • So basically I am reposting as two separate posts for boletes I found under Quercus ilex, fruiting early in October, in calcareous substrate present in the Msltese Islands, maybe someone is familiar with them.

    This collection often formed thick stipes and spherical reddish to reddish-brown pileus not much broader from the stipe (probably it will extend to a convex shape when fully mature).

    Reddish-brown, somewhat in three zones, the central more reddish to reddish brown, then a faded potion and turning bark brown at the border, then a whitish lining at the margin

    Stipe light yellow, with golden hues, then reddish streaks or flushes at the lower half which becomes more intense after collection

    When cut the upper half remains light yellow, but below it forms reddish streaks which intensify towards the base. The colouring is most intense just under the cuticle at the base. A faint blue color was observed after time or cutting a specimen collected after 12 hours

    Hymenium or stipe do not change colour when bruised

    Scent faint mildly fungal, not of anything distinct. Taste palatable, good-tasting, mushroom-like but not of anything distinct too.

    Pores rounded, about 0.3mm diameter, circular to more often oval-ellipsoid, irregular and sometimes coalescing forming elongated (linear) shapes up to 1.2mm long

    Spores fusiform-navicular with a tiny germ pore at one pole and a small eccentric apicullum at the other. Contents with 2-3 large oil drops sometimes with few smaller ones. Measurement: 9.7 [11 ; 11.6] 12.9 × 4.7 [5.3 ; 5.5] 6.1 µm [ Me = 11.3 × 5.4 µm ; Qe = 2.1]. Spore mass dull olive-brown, darkens slightly in KOH.

    I.considered Hortiboletus rubellus and Hortiboletus (Xerocomus) cisalpinus or just again abnormal specimens of X. redeuilhii (also present there) but not so happy with any of these three.

  • Hi.

    Maybe I'm mistaken but a few spores look like they are truncate. If so (check in 1000x), maybe consider Xerocomellus marekii which is a red color form of X. porosporus.

    I'm not sure however. Xerocomellus fennicus is supposedly similar but it's hard to find information about it. The few descriptions I found say that it favors Betula and Alnus however.

    If you have some dried material which isn't affected by Hypomyces a sequence might be interesting.


    Bin lediglich fortgeschrittener Anfänger.
    Posts sind nicht als Essensfreigabe zu verstehen. :-]

  • Xerocomellus marekii : love:

    X. marekii « boletales.com

    Pablo - I love your suggestion !!!! I see truncate spores (but not all ??!) and habitat (under oaks), colours, flesh when cut (including the bluening), small hemisherical head of this species are matching nicely. I think I have to sequence this collection at this point. About C. fennicus, I thought its distribution is more north, in acidic soils not under oaks. I try to watch again the spores carefully.

    Reference is made to striated spores.... Is this best checked at x 1000 in cotton blue or cresyl blue ?

  • Hi.

    I'd check the spore shape in water. I think cotton blue is lethal to the spores and might lead to collapsing spores rather quick. You don't really need to stain the spores here.

    It's normal for the boletes with truncate spores that not all of them are truncate but you should be able to spot some every now and then. Especially the ones in the upper right corner you circled do seem rather truncate in your picture but like I said, best to check again under oil immersion to be sure.


    Bin lediglich fortgeschrittener Anfänger.
    Posts sind nicht als Essensfreigabe zu verstehen. :-]

  • I am reading the discussion... those I highlighted in green match well, those in red do not match with my specimen (in my opinion!) Those left unhighlighted not important or distict

    Characteristic features of Boletus marekii can be summarised as follows: fruit

    bodies relatively small, of a xerocomoid appearance; pileipellis red-coloured from

    youth, e.g. orange-red, bright red, carmine to dark red, soon cracking and then

    coarsely rimose-areolate over the entire pileus surface, consisting of

    a palisadoderm with weakly incrusted hyphae; both tubes and pores yellow,

    slightly bluing or pale blue-greening when injured, pores in maturity relatively

    large (about 1 mm); spores smooth and truncate; stipe light yellow to whitish yellowish,

    in the middle sometimes dirty reddish, dirty red-brownish or wine-reddish;

    context in the pileus and upper half of the stipe pale yellowish, when cut

    slightly bluing. This species can be easily recognised by its red-coloured pileipellis

    and the truncate, smooth spores. Such a combination of characters is quite exceptional,

    not occurring in any other species of the Boletaceae.

    B. marekii belongs to Boletus L. subgen. Xerocomus (Quél.) Maubl. and macroscopically

    is rather similar to some species of the B. chrysenteron group, particularly

    Boletus armeniacus Quél., Boletus ripariellus (Redeuilh) Watling and Boletus

    fennicus (Harmaja) Šutara, partly also Boletus porosporus (Imler) ex

    Watling, Boletus rubellus Krombh. and a reddish form of Boletus declivitatum

    (C. Martin) Watling.

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