Polyporus arcularius

Scientific name:   Polyporus arcularius Batsch: Fr.
Derivation of name:   Polyporus means "many pores";
arcularius means "with small boxes" in reference to the
pores.
Synonymy:   Boletus arcularius Batsch
Common names: Spring polypore. 
Phylum:   Basidiomycota
Order:   Polyporales
Family:   Polyporaceae
Occurrence on wood substrate: Saprobic; solitary or in
groups on decaying deciduous wood or attached to buried
wood; April through June.   
Dimensions: Caps 1-8 cm wide; stipes 2-6 cm long and
1.5-4.5 mm thick, central, colored like the cap.   
Upper surface: Dark brown when young, becoming yellow-
brown in age; dry; scaly; margin lined with conspicuous hairs.
Pore surface: White to pale yellow; pores polygonal to
angular, radially arranged; pores 0.5-1 per mm.
Edibility: Inedible.
Comments: One of the first mushrooms to appear in the
spring. Compare to P. brumalis which has a darker cap
without a fringed margin and smaller pores.

More information at MushroomExpert.com:  


Figure 1. Polyporus arcularius on wood. The caps often
have a depressed center. Photo © John Plischke III.

Figure 2. Collected specimens. Photo © Dorothy Smullen.

Figure 3. Collected specimens. Photo © Tom Volk.

Figure 4. A characteristic feature of the spring polypore is
the fringe of hairs around the margin. Photo © Tom Volk.

Figure 5. Close-up of the marginal hairs. Photo © Tom Volk.