Butyriboletus regius

Description

Butyriboletus regius is a basidiomycete fungus of the genus Boletus. The cap is up to 20 cm wide, pink, dark pink to pinkish red, dry, smooth, and not blueing when bruised. Stem cylindrical to club-shaped, distinctly swollen or tapering towards the base, lemon yellow or bright yellow, in the base sometimes with red to dark red spots (especially when dried), entirely or at least in the upper half with a well-developed network, stem surface not blueing when bruised. Flesh lemon yellow or bright yellow, sometimes pale pink to dirty pink at the stem base, not blueing when exposed to air, occasionally somewhat reddening when dried.

This ectomycorrhizal mushroom is found singly or in very small groups under various kinds of oaks as well as Beech and Sweet Chestnut trees in calcareous regions. Rare in European countries, noticeably Italy, France, Spain, Portugal, and in some parts of North America and China.

Common names: Royal Bolete, Red-Capped Butter Bolete, Königsröhrling (German), Hřib královský (Czech Republic), Masłoborowik Królewski (Poland).

Mushroom Identification

1. Cap

   7–20 cm (2.8–7.9 in) wide. The cap surface is pink to red, occasionally with hints of yellow or brown, more so around the margin. Initially velvety to slightly tomentose (hairy) when young, these minute hairs tend to slough off with age, and the cap develops wrinkles and pits. The cap flesh is yellow, and slowly and erratically bruises blue in North American specimens.

2. Pores and Tubes

   The pores on the underside of the cap are angular, and measure about 1–2 per millimeter. The color of the pore surface is a bright yellow to start, but eventually darkens somewhat, and will stain blue with damage. The depth of the tubes comprising the pores extends to 0.8–2.5 cm (0.3–1.0 in).

3. Stem

   The stem measures 5–13 cm (2.0–5.1 in) long by 2.5–5 cm (1.0–2.0 in) thick, and typically has a thick, bulbous base. It is solid (i.e., not hollow), and bright yellow color, often with reddish tones, particularly near the base of the stem. The stem surface can be covered with fine yellow reticulations either throughout its length, or just on the upper portion.

4. Spores

   Its smooth, hyaline (translucent) spores are roughly elliptical to somewhat fusoid (wider in the middle and tapering toward the ends) to more or less cylindrical, and have dimensions of 12–17 by 4–5 μm.

5. Spore Print

   Olive-brown.

6. Chemical Reaction

   The cap cuticle will stain a pale purple color if FeSO4 is applied; this same test will turn the flesh grayish.

7. Habitat

   It is an ectomycorrhizal species with a broad host range, and associates with oak and conifers, particularly fir. Fruit bodies grow singly, scattered about, or grouped together. In North America, they usually appear from August to November, although they also appear between May and June. The North American distribution includes the Pacific Northwest states of California, Oregon, and Washington, where its frequency of occurrence ranges from "rare to locally abundant". It is rare in Europe, appearing on the Regional Red List of several countries, and is considered endangered in the Czech Republic. The species has also been recorded from China.

Look-Alikes

1. Hortiboletus rubellus

   Much smaller and has a ruby-red cap. The stem is striate rather than reticulate.

2. Boletus pseudoregius

   Has dull pink to pinkish-brown cap, yellow blueing flesh, blueing tubes and pores, and spores of different sizes.

3. Boletus kluzakii

   It may have similarly colored fruitbodies but it has blueing flesh and bitter taste.

4. Boletus spretus

   It also has a reddish cap, but this one has a compact reddish dot on the bottom of the stem and turns blue when cut or damaged.

History

In 1832 Julius Vincenz von Krombholz described this species and named it Boletus regius. This name was retained until 2014 when Americans David Arora and Jonathan L. Frank transferred it to the new genus Butyriboletus.

Butyriboletus regius was formerly classified as a member of the section Appendiculati of the genus Boletus. Molecular analysis demonstrated that this and related "butter bolete" species, including Boletus appendiculatus, are phylogenetically distinct from Boletus, and the new genus Butyriboletus was created to contain them.

The generic name Boletus comes ​​from the Greek "bolos", meaning "lump of clay", and the butyri- prefix means "buttery".

Synonyms

• Boletus regius Krombh. (1832)

• Boletus appendiculatus subsp. regius (Krombholz) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 160

• Boletus appendiculatus var. regius (Krombholz) Costantin & L.M. Dufour (1891), Nouvelle flore des champignons, Edn 1, p. 152

• Boletus subtomentosus subsp. cerasinus C. Martín (1903), Materiaux pour la Flore cryptogamique Suisse, 2(1), p. 32

• Butyriboletus regius (Krombholz) D. Arora & J.L. Frank (2014), Mycologia, 106(3), p. 466

• Dictyopus appendiculatus var. regius (Krombholz) Quélet (1886), Enchiridion fungorum in Europa media et praesertim in Gallia vigentium, p. 160

• Dictyopus regius (Krombholz) Quélet (1888), Flore mycologique de la France et des pays limitrophes, p. 424

• Suillus regius (Krombholz) Kuntze (1898), Revisio generum plantarum, 3, p. 536

• Tubiporus regius (Krombholz) P. Karsten (1882), Bidrag till kännedom af Finlands natur och folk, 37, p. 5

Photo sources:

Photo 1 - Author: GLJIVARSKO DRUSTVO NIS from Serbia (CC BY-SA 2.0)

Photo 2 - Author: Gerhard Koller (Gerhard) (CC BY-SA 3.0)

Photo 3 - Author: Phalluscybe (phonehenge) (CC BY-SA 3.0)

Photo 4 - Author: Shane (Mushane) (CC BY-SA 3.0)

Photo 5 - Author: pennybun (pennybun) (CC BY-SA 3.0)