Summary:
Features include 1) a light brown to dark yellowish brown or maroon fruitbody that is spherical or pear-shaped, 2) a fleshy spore mass with small chambers radiating somewhat from the base, white to yellowish becoming cinnamon brown, 3) a stem that is white with a velvety surface, and 4) microscopic characters including spores with longitudinal ridges on 2-spored and 4-spored basidia. It is frequently parasitized by Hypomyces chrysospermum, (Smith). Trappe(13) says it is rare in the Pacific Northwest. Chamonixia ambigua (Zeller & C.W. Dodge) A.H. Sm. & Singer is illustrated by Desjardin(6) for CA and given as a synonym of Chamonixia caudata by the Index Fungorum, accessed January 20, 2015 and May 29, 2019.

Interior:
fleshy; "chambers small, irregular and radiating somewhat from the base of the columella"; white to yellowish, cinnamon brown when old or when dried, (Smith)

Microscopic:
spores 9-15 x 9-11 microns, elliptic to ovate, "the primary ornamentation in the form of longitudinal ridges irregular in shape and extending from over one half to the full length of the spore, the secondary ornamentation as cross ridges and tubercles, causing the spores to appear reticulate at times", with distinct apical pore, inner wall thick (1.5-2 microns), spores dark red brown in Melzer''s reagent, dull brown in KOH; basidia 2-spored and 4-spored, the sterigmata prominent; cystidia and paraphyses not seen (hymenium revived poorly, according to Zeller and Dodge cystidia large, clavate, and colorless and paraphyses 19-20 x 4-5 microns, cylindric, obtuse, colorless, and septate); hyphae of tramal plates poorly revived (according to Zeller and Dodge of loosely interwoven, colorless hyphae); "epicutis of peridium a trichodermium of septate hyphae in which the cells are narrowed to the cross walls and some of the apical cells actually become separated"; clamp connections not seen, (Smith), spores 9-15 microns long, with apical pore, (Arora), basidia 24-26 x 9-13 microns, sterigmata short, stout, 3-6 microns long; peridium 200-300 microns thick in upper part, very thin or wanting below, "composed of radial septate hyphae perpendicular to the surface, forming pseudoparenchymatous tissue having cells about 9-10 x 11-13 microns, the septa of the hyphae becoming constricted and finally abjointing spherical to oblong oidia-like cells from the surface of the peridium", (Zeller)

Notes:
Chamonixia caudata has been found at least in OR and CA (Smith). It occurs from southwestern OR to northern CA, (Trappe(13)). This species was identified and vouchered from Vancouver Island in BC by O. Ceska although the spore size was estimated at 14 x 7 microns, a little narrower than figures given here.

Synonyms and Alternate Names:
Phellinus ferreus (Pers.) Bourdot & Galzin
Polyporus ferreus Pers.