Irpex lacteus

Scientific name:   Irpex lacteus (Fr.) Fr.
Derivation of name:   Irpex means "a large rake with
iron teeth"; lacteus means "milky."
Synonymy:   Polyporus tulipiferae (Schw.) Overh.
Common names:   Milk-white toothed polypore.
Phylum:   Basidiomycota
Order:   Polyporales
Family:   Phanerochaetaceae
Occurrence on wood substrate: Saprobic; on dead
branches of deciduous trees; year-round.   
Dimensions:  Caps (when present) 1-4 cm wide.   
Upper surface:  Growth entirely resupinate to effused-
reflexed; caps (when present) whitish, drying yellowish;
velvety hairy.
Pore surface: White to cream, dingy yellow in age; tubes
breaking up into flattened teeth up to 6 mm long.
Comments: As reflected in the order name, Polyporales,
Irpex lacteus is actually a poroid fungus. The brackets
often fuse to form long rows. The caps may be very small
in comparison to the spreading, resupinate portions of this
fungus. Compare to Xylodon paradoxus, a potential
look-alike species.

More information at MushroomExpert.com:  


Figure 1. Irpex lacteus on a hardwood branch.
Photo © Gary Emberger.


Figure 2. Note how milk-white toothed polypore caps fuse
to form long rows, often with a substantial resupinate area.
Photo © Larry Grand.

Figure 3. Many individual effused-reflexed specimens.
Photo © William Roody.

Figure 4. The tube walls disintegrate in such a manner that
flat tooth-like portions remain to form the fertile surface.
Photo © Gary Emberger.

Figure 5. The individual teeth may be several mm in
length. Photo © Gary Emberger.