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Page number:73 
Remarks (public):The above New Zealand collection once again illustrates the difficulty of drawing dividing lines between the taxa of the Hydnum repandum-complex.
Peck's description of H. umbilicatum runs thus: "Pileus fleshy, convex, glabrous, umbilicate, reddish buff or burnt sienna color, flesh white, taste mild; aculei plane in the mass [which, of course, is a printer's error], fragile, nearly equal, a little paler than the pileus; stem nearly equal, glabrous, solid, whitish ; spores globose, .0003-.0004 of an inch in diameter [which equals 7.6-10.2 µm]."
Banker (1906: 109) subdividing H. repandum into three forms thought that his form A would correspond to H. umbilicatum, but he added that "In all of the above forms none of the characters ascribed appear to be constant, while intermediate forms are readily found that connect them most intimately."
Miller & Boyle (1943: 58) simply merged H. umbilicatum with what they called Dentinum repandum, probably because that was in keeping with Banker's later concept in an unpublished manuscript (Coker & Beers, 1951: 18).
Coker & Beers (1951: 18) reintroduced H. umbilicatum on the grounds that the specimens they had described "agree so well with Peck's description and are so conspicuously different from repandum ..." and "differ in darker color, consistently slender stature (thinner flesh and relatively longer stems), redder and usually umbilicate cap, larger spores, no trace of acrid taste, and when dry in the more delicate and flexuous spines."
Harrison (1961: 19) also treated H. umbilicatum as a separate species, differing from H. repandum in being smaller and having an umbilicate pileus, but allowing it to be "similar in color."
I am inclined to follow Coker & Beers who tried hard to find characteristics convincingly to separate H. umbilicatum from H. repandum, but I am not blind to Banker's words quoted above.
Description type:Non-original description 
Description:Hydnum umbilicatum Peck-Figs. 98-100, Pl. I, fig. 1
[Undescribed form, Peck in Rep. N.Y. St. Mus. 54: 171. 1901. - ] Hydnum umbilicatum Peck in Bull. N.Y. St. Mus. 54: 953. pl. K figs. 14-18. 1902. - Dentinum umbilicatum (Peck) Pouz. in Ceská Mycol. 10: 76. 1956. - Type: not seen (NYS).
Basidiomes solitary. Pileus 20-30 mm across, plano-convex to hemispherical, slightly to deeply umbilicate, smooth, fibrillose to more or less fibrillose-scaly, orange-brown to red-brown. Stipe 20-40 x 4-7 mm, central or excentric, solid, cylindrical, curved and more or less enlarged to bulbous below, somewhat felted to glabrescent, pink-fawn to orange-brown. Spines up to 5 mm long, free from the stipe or slightly decurrent, moderately crowded to subdistant, subulate, creamy. Context of the pileus up to about 3 mm thick, creamy.
Context of the pileus monomitic. Generative hyphae up to 18 µm wide, inflating, thin-walled, branched, septate, with clamp-connections to all septa. Context of the spines similar, hyphae narrower. Basidia at least 35-45 x 9 µm, but either immature or collapsed and many anomalous, cylindrical-clavate, with basal clamp-connection. Spores 8.1-9.5 x 7.2-7.8 µm, broadly ellipsoid to subglobose, smooth, colourless, with granular contents, with oblique apiculus.

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