The cap of Bothia castanella is convex at first before flattening out in age, reaching a diameter of 3–8 cm (1.2–3.1 in).
The center of the cap sometimes acquires a shallow depression, while the margin ranges from even to wavy and irregular.
The cap surface is dry and initially hairy, but becomes smooth in maturity.
Its color ranges from reddish brown to burgundy-brown to dark yellowish brown.
The flesh is white, and, unlike several other bolete species, does not change color when bruised or injured.
It is about 8 mm (0.3 in) thick.

On the cap undersurface are the pores, which are angular to elongated and measure about 2 mm wide.
The color of the pore surface is pinkish brown to tan or buff, but it becomes yellowish brown in maturity; bruised areas turn ochre-tawny.
The tubes are somewhat decurrent attached to the stipe (i.e., running slightly down its length), and extend about 6 mm (0.24 in) deep.
The mushroom lacks any appreciable odor or taste.
The dry, solid stipe measures 2–7 cm (0.8–2.8 in) long by 0.6–2 cm (0.2–0.8 in) thick, and is nearly equal in thickness throughout, or slightly tapered on either end.
Its surface is more or less smooth except for a reticulate (meshed) area at the apex.
The edibility of the mushroom is unknown.

Fruit bodies produce a yellow-brown spore print.
Spores are egg-shaped to ellipsoid, smooth, thin-walled, and measure 8.4–10.5 by 4.2–4.9 µm.
The basidia (spore-bearing cells) are club-shaped, four-spored, and measure 25–35 by 7–9 µm.
Cystidia are present on both the tube walls (as pleurocystidia) and abundantly on the edges (as cheilocystidia).
They are somewhat spindle-shaped, sometimes with a central swelling, and measure 45–70 by 7–12 μm.
Clamp connections are absent from the hyphae, and all of the hyphae are inamyloid.

Several chemical tests can used to help confirm identification of the mushroom.
The cap cuticle turns grayish with the application of a drop of ferrous sulfate (FeSO₄), and dark brown to amber with a dilute solution of potassium hydroxide (KOH).
The flesh turns pale brown with KOH, and pale yellow with ammonia (NH₄OH).
The cap of Bothia castanella is convex at first before flattening out in age, reaching a diameter of 3–8 cm (1.2–3.1 in). The center of the cap sometimes acquires a shallow depression, while the margin ranges from even to wavy and irregular. The cap surface is dry and initially hairy, but becomes smooth in maturity. Its color ranges from reddish brown to burgundy-brown to dark yellowish brown. The flesh is white, and, unlike several other bolete species, does not change color when bruised or injured. It is about 8 mm (0.3 in) thick.
On the cap undersurface are the pores, which are angular to elongated and measure about 2 mm wide. The color of the pore surface is pinkish brown to tan or buff, but it becomes yellowish brown in maturity; bruised areas turn ochre-tawny. The tubes are somewhat decurrent attached to the stipe (i.e., running slightly down its length), and extend about 6 mm (0.24 in) deep. The mushroom lacks any appreciable odor or taste. The dry, solid stipe measures 2–7 cm (0.8–2.8 in) long by 0.6–2 cm (0.2–0.8 in) thick, and is nearly equal in thickness throughout, or slightly tapered on either end. Its surface is more or less smooth except for a reticulate (meshed) area at the apex. The edibility of the mushroom is unknown.
Fruit bodies produce a yellow-brown spore print. Spores are egg-shaped to ellipsoid, smooth, thin-walled, and measure 8.4–10.5 by 4.2–4.9 µm. The basidia (spore-bearing cells) are club-shaped, four-spored, and measure 25–35 by 7–9 µm. Cystidia are present on both the tube walls (as pleurocystidia) and abundantly on the edges (as cheilocystidia). They are somewhat spindle-shaped, sometimes with a central swelling, and measure 45–70 by 7–12 μm. Clamp connections are absent from the hyphae, and all of the hyphae are inamyloid.
Several chemical tests can used to help confirm identification of the mushroom. The cap cuticle turns grayish with the application of a drop of ferrous sulfate (FeSO₄), and dark brown to amber with a dilute solution of potassium hydroxide (KOH). The flesh turns pale brown with KOH, and pale yellow with ammonia (NH₄OH).
Bothia