''Rheubarbariboletus armeniacus'' is a small mushroom in the family

Boletaceae The Boletaceae are a family of mushroom-forming fungi, primarily characterised by small pores on the spore-bearing hymenial surface (at the underside of the mushroom), instead of gills as are found in most agarics. Nearly as widely distributed ...

native to Europe. It was formerly placed in the genera ''

Boletus ''Boletus'' is a genus of mushroom-producing fungi, comprising over 100 species. The genus ''Boletus'' was originally broadly defined and described by Carl Linnaeus in 1753, essentially containing all fungi with hymenial pores instead of gil ...

'', ''

Xerocomus ''Xerocomus'' is a genus of poroid fungi related to ''Boletus''. Many mycologists did not originally recognize the distinction between the two genera and placed ''Xerocomus'' taxa in genus ''Boletus''. However, several molecular phylogenetic stu ...

'', and ''

Xerocomellus ''Xerocomellus'' is a genus of fungi in the family Boletaceae. The genus, as it was described in 2008, contained 12 species. However '' X. rubellus'' and '' X. engelii'' were transferred to the new genus '' Hortiboletus'' and '' X. armeniacus'' ...

''. It acquired its current name when it was transferred to genus '' Rheubarbariboletus'' in 2015.

Taxonomy

French naturalist

Lucien Quélet Lucien Quélet in 1869 Lucien Quélet (14 July 1832 – 25 August 1899) was a French naturalist and mycologist. Quélet discovered several species of fungi and was the founder of the Société mycologique de France, a society devoted to mycolo ...

described this species as ''Boletus armeniacus'' in 1885, before placing it in the genus ''

'' in his 1888 work ''Flore mycologique de la France et des pays limitrophes'' (''Mycological flora of France and neighbouring countries''). It was transferred to the new genus ''

'' described by Czech mycologist Josef Šutara in 2008, and then to '' Rheubarbariboletus'' in 2015.

Description

The

cap A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. Caps typically have a visor, or no brim at all. They are popular in casual and informal se ...

is initially globular before expanding to become convex and flattening somewhat; it grows to a diameter of . The cap margin initially adheres to the stipe and has a tendency to become lobed or undulated in age. The cap surface is first somewhat

pubescent The adjective pubescent may describe: * people or animals undergoing puberty * plants that are hairy, covered in trichomes * insects that are covered in setae In biology, setae (singular seta ; from the Latin word for "bristle") are any of a ...

but later becomes smooth and hairless, and may develop cracks in age. Its color is orangish-

apricot An apricot (, ) is a fruit, or the tree that bears the fruit, of several species in the genus ''Prunus''. Usually, an apricot is from the species '' P. armeniaca'', but the fruits of the other species in ''Prunus'' sect. ''Armeniaca'' are also ...

, aging to

ochre Ochre ( ; , ), or ocher in American English, is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It is also the name of the colours produced ...

. Tubes are initially pale yellow, but become more vivid in age, and eventually develop greenish-yellow to greenish-olive tones. They will become pale blue upon with bruising. The pores are circular or a bit angular, with the same coloring and bruising reaction as the tubes. The robust stipe measures long by thick. It is usually thicker in the middle or lower region, and its base roots into the substrate. The top part of the stipe is yellow; under this the coloration tends to be masked by a dense and fine reticulation that becomes brown to brownish-crimson in age. In some specimens the stipe cuticle cracks and pointed patches lift from the surface. The

flesh Flesh is any aggregation of soft tissues of an organism. Various multicellular organisms have soft tissues that may be called "flesh". In mammals, including humans, ''flesh'' encompasses muscle Skeletal muscles (commonly referred to as mu ...

is pale yellow in the cap, with a narrow strip of pinkish-yellow under the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

; in the stipe, the flesh is orange-ochre, with a reddish tint. The flesh sometimes shows a slight and temporary color change to blue when cut or otherwise injured, but this feature is not consistent. It has a pleasant odor and a fruity-acid taste.

Spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

are

fusiform Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon-shape, but often implies a focal broadening of a structure that continues from one or both ends, such as an aneurysm on a b ...

(spindle shaped), measuring 10–15 by 4.5–6

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

. The

basidia A basidium () is a microscopic sporangium (a spore-producing structure) found on the hymenophore of fruiting bodies of basidiomycete fungi which are also called tertiary mycelium, developed from secondary mycelium. Tertiary mycelium is highly-c ...

(spore-bearing cells) are club-shaped, four-spored, and contain internal oil droplets; they measure 28–35 by 9–12 µm. The

cystidia A cystidium (plural cystidia) is a relatively large cell found on the sporocarp of a basidiomycete (for example, on the surface of a mushroom gill), often between clusters of basidia. Since cystidia have highly varied and distinct shapes that ar ...

are fusiform,

hyaline A hyaline substance is one with a glassy appearance. The word is derived from el, ὑάλινος, translit=hyálinos, lit=transparent, and el, ὕαλος, translit=hýalos, lit=crystal, glass, label=none. Histopathology Hyaline cartilage is ...

(translucent), and 40–55 by 9–12 µm.

Ecology

It has been recorded forming

ectomycorrhiza An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobi ...

l association with white poplar (''

Populus alba ''Populus alba'', commonly called silver poplar,Webb, C. J.; Sykes, W. R.; Garnock-Jones, P. J. 1988: Flora of New Zealand. Vol. IV. Naturalised Pteridophytes, Gymnosperms, Dicotyledons. 4. Christchurch, New Zealand, Botany Division, D.S.I.R. si ...

'') in Hungary. Its ectomycorrhizae contain bright yellow

pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

, especially the

rhizomorph Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functio ...

s, and have warts on the outer surfaces of both the rhizomorphs and the mantle. The ectomycorrhizae of ''R. armeniacus'' cannot be reliably distinguished from those of ''

Xerocomus subtomentosus ''Xerocomus subtomentosus'', commonly known as suede bolete, brown and yellow bolete , boring brown bolete or yellow-cracked bolete, is a species of bolete fungus in the family Boletaceae. The fungus was initially described by Carl Linnaeus in 17 ...

''.

References

{{Taxonbar, from=Q54371403, from2=Q923521 Boletaceae Fungi of Europe Fungi described in 1885 Taxa named by Lucien Quélet