The boletes of Michigan, by Alexander H. Smith and Harry D. Thiers.

BOLETUS 263
5. Terminal cells of pilear trichodermium dingy brown in KOH.................................. see B. chrysenteron var. chrysenteron
5. Not as above....................................... 6
6. Spores 10-12.5 x 3-4.......................... B. rubeus
6. Spores 4-5.5 L wide................................ 7
7. An occasional cell of the trichodermial hyphae having an apical proliferation................... see B. chrysenteron var. subnudipes
7. Not as above..................... (but see B. subfraternus also) 8
8. Pileus dark dull red...................B. rubellus var. rubellus
8. Pileus flame-red....................B. rubellus var. flammeus
136. Boletus flavorubellus Thiers & Smith
Mich. Bot. 5:117. 1966
Illus. P1. 125 (upper).
Pileus (2.5) 5-6 (8) cm broad, convex to pulvinate, becoming
broadly convex; surface dry and subtomentose, soon deeply areolate
exposing the yellow context; the margin fertile, color deep red ("brickred" to "Hay's russet"), gradually paler and in age at times chromeyellow. Context bright rich yellow (flavous), slowly changing to greenish
blue when cut, with KOH ochraceous-tan, with FeSO4 grayish; taste
mild, odor none.
Tubes sharply depressed at the stipe, 4-5 mm deep, flavous staining greenish blue bruised; pores small (2-3 per mm), angular to round,
flavous staining greenish when bruised.
Stipe 3-7 cm long, 5-11 mm thick, equal, solid, flavous within,
streaked reddish around larval tunnels, slowly staining greenish where
cut; surface above flavous beneath the reddish pruinose coating, flavous
below, tinged red in the midportion, base with yellow-ocher mycelium.
Spore deposit dark olive; spores compressed to some degree,
10-13 X 4-5 X 4.5-7 gt, smooth, ovate to ventricose-ovate in face view, in
profile subelliptic to inequilateral or ventricose-inequilateral, dingy ochraceous in KOH, in Melzer's a dull yellowish tan with a slight greenish
gray shadow when first mounted, wall slightly thickened, with a minute
apical thin spot.
Basidia 4-spored, 20-24 X 8-10 a, clavate, yellowish in KOH.
Pleurocystidia scattered, 3040 X 9-12 u, fusoid-ventricose, apex obtuse,
nearly buried in the hymenium and with content merely yellowish in
KOH and Melzer's. Tube trama somewhat gelatinous, hyphae slightly
divergent from a central area to nearly parallel. Pileus trichodermium of
short-celled hyphae 12-20 u broad and 2-3 times as long, but some