Manzanita Bolete Identification Guide

Where and When

This is a fungus of western North America, from the California coast ranges and Sierra foothills north into Oregon, and it is tied to a particular kind of vegetation: manzanita thickets and chaparral, the manzanita understorey of mixed oak and conifer woodland, and stands with Pacific madrone. The season follows the winter rains, roughly November into February at low elevation and earlier higher up.

What you see is a large, solid, dark bolete standing among the crooked red stems of Arctostaphylos. The cap is deep red-brown or maroon, often shining after rain, and the stem below it is pale and coarsely stippled with black. Size alone is striking; this is one of the biggest Leccinums anywhere, and a mature one can carry a cap the width of a dinner plate on a stem as thick as a wrist.

Reading the Cap

Diameter runs from 8 to 20 cm and sometimes to 30 cm. The shape moves from hemispherical, almost spherical in buttons, through convex to broadly flattened, with the margin staying tucked under for a long time.

Colour is dark and warm: deep red-brown, maroon, brick, dark reddish-tan, fading to duller brown or paler tan on old, sun-exposed fruit bodies. The surface is minutely felted or matted when young and smooths with age, and it is distinctly slippery in wet weather, drying to a low shine.

Check the margin specifically. A narrow flap of sterile tissue projects beyond the tube layer all the way round, so the cap overhangs the pores like a small brim. That overhanging sterile margin is a genus character in Leccinum but it is unusually well developed in this species, and with age it becomes ragged and toothed. Run a finger under the rim to feel it.

Pores and Tubes

The pore surface is whitish to pale buff or grey-buff at first and dulls to olive-buff or brownish as the fruit body matures. Pores are small and round, roughly one or two per millimetre, and they bruise dull brown to olive-brown where pressed rather than blue.

The tube layer is deep, up to about 3 cm, and clearly depressed around the top of the stem so that there is a shallow moat where the two meet. It separates cleanly from the cap flesh as a distinct layer if you lever it with a knife, which is normal for boletes and worth confirming.

The Stem: Scabers Are the Genus Test

The stem is 10 to 20 cm long and 2 to 5 cm thick, often club-shaped and thickest below, sometimes tapering, solid and firm throughout.

The ground colour is whitish to pale grey. Over it, from top to bottom, sits the ornamentation that defines Leccinum: scabers. These are small projecting tufts of dark hyphae, arranged roughly in vertical lines, giving the stem a coarse stubbled or stippled texture that you can feel with a thumb. In this species they start whitish to grey and blacken with age, so a mature stem looks heavily flecked in black on pale grey.

The crucial contrast is scabers versus a network. A network, or reticulum, is a raised continuous mesh of ridges enclosing cells, and it is what you find on Boletus edulis and its relatives. Scabers are separate, discrete, tufted points that never join. Put a lens on the middle of the stem and decide which you are looking at before anything else.

The extreme base often shows blue-green or blue-grey staining in the flesh, which is normal and not to be confused with a general bluing reaction.

Flesh and the Colour-Change Sequence

Cut the whole fruit body in half lengthways and then watch the cut face for a full ten minutes; a single glance will miss the most useful character.

The flesh is thick, firm and white. On exposure it stains slowly and in stages: first a pinkish or vinaceous grey flush spreads through the cap flesh and upper stem over a minute or two, then it deepens to grey, and finally, over several minutes, to a dark greyish-black. The lower stem may go blue-green instead. That multi-stage sequence, pink then grey then near-black, is the most reliable confirmation available without a microscope, and it is what separates the group from boletes that either do not change or turn blue immediately.

The smell is mild and pleasantly fungal. There is no latex.

Spore Print

Boletes are slow depositors. Cut the stem off flush, lay the cap pore surface downward on white paper, cover it with a bowl to hold the humidity, and leave it six to twelve hours or overnight.

The print is olive-brown to dull yellow-brown, standard for the genus and useful mainly to confirm you have a bolete rather than a gilled fungus with a false pore surface. Under a microscope the spores are long and narrow, smooth and roughly spindle-shaped, in the region of 13 to 18 by 4 to 5 µm.

Substrate, Partners and Ecology

This is an ectomycorrhizal fungus, and its partnerships are unusually narrow. It associates with manzanita, Arctostaphylos, and to a lesser degree with Pacific madrone, Arbutus menziesii. Both are members of the heath family, and the fungus is essentially absent where they are absent, even if oaks and pines are abundant.

In practice that means you search the drip line of manzanita shrubs and the duff under madrone, often finding fruit bodies half-buried under leaf litter and moss with only a dark dome showing. Fruit bodies are usually solitary or scattered rather than clustered. Because the associated shrubs are long-lived and slow-growing, productive thickets are worth revisiting year after year.

Separating the Look-Alikes

Leccinum aurantiacum and L. insigne, the aspen and birch boletes, have bright orange to orange-red caps rather than dark maroon, scabers that are reddish-brown or brown at first and only later dark, and completely different partners: aspen, poplar or birch. Both cap tone and the surrounding trees separate them.

Leccinum scabrum, the birch bolete, has a dull grey-brown to tan cap with no red in it, distinctly soft and watery flesh, grey-black scabers on white, and staining that is faint and mostly pinkish or absent. It is strictly a birch associate.

Other dark-capped western Leccinum species overlap considerably, and here you rely on the combination of very large size, well-developed overhanging sterile cap margin, dark maroon cap and the specific manzanita or madrone association.

Boletus edulis and its western relatives grow in the same woods, but their stems carry a raised white network rather than scabers, their pores are white then yellow-olive, and the flesh does not change colour on cutting. The stem ornamentation test settles this pair instantly.

Suillus species under pines have slippery caps too, but the pores are large and angular or arranged in radial rows, and many have a ring or glandular dots on the stem.

Tylopilus species have pinkish pore surfaces and either a smooth or a netted stem.

What to Photograph

One image of the stem surface close enough to resolve individual scabers, one of the cap margin from underneath showing the overhanging flap, one of a cut section taken five to ten minutes after cutting so the stain is developed, and a wide shot showing the manzanita or madrone within a few metres. Those four make the record verifiable.