North Island: WKR, Te Matua Ngahere, base of big tree, 31.v.82, coll. RHP, no. 43541 (holotype, PDD; isotype, TENN); Auckland, Orere, 4.vii.81, coll. EH, no. 1042 (ZT); OSF, 5.v.81, coll. EH, no. 604 (ZT); WR, Cowan Track, 4.vi.83, coll. GS & A Rossman, s.n. (PDD); Auckland, Titirangi, Atkinson Park, 20.vi.65, coll. RFRM, no. 64 (PDD). South Island: PSR,19.v.83, no. 43540 (TENN).

Fruit bodies up to 60 x 4 mm, simple clubs, solitary to cespitose in groups of 2-3, arising from a small, whitish mycelial patch. Stipe equal, pallid at base ("tileul buff") grey above ("pale neutral-grey"), appearing silky. Club matte on surface, equal, often somewhat wrinkled or subsulcate, grey to bluish grey ["neutral-grey", "7 grey" "deep dull grey", "deep plumbeus", "mouse-grey"]; flesh more deeply coloured than hymenium outward, paler and more fibrous or stuffed within. Apex rounded. Taste and odour negligible.
Macrochemical reaction: FCL = negative.
Tramal hyphae of club 3-20 µm diam., hyaline, unclamped, thin-walled, strictly parallel, covered with small patches of amorphous material, and with occasional crystals. Subhymenium extensive, pseudoparenchymatous. Hymenium thickening; basidia 70-80 x 10-13 µm, broadly clavate, bifurcate or clamped at base, more or less persistent after spore discharge; contents granular to multiguttulate at maturity; sterigmata (2-3)-4, stout, arising as rounded lobes, eventually up to 10 µm long, curved-ascending.
Spores (Fig. 28) 9.4-11.2 x 7.9-9.0 µm (E = 1.08-1.41; E^m = 1.21; L^m = 10.3 µm), broadly ellipsoid, conspicuously roughened; contents multiguttulate to uniguttulate; hilar appendix broad, papillate; ornamentation of narrowly truncate-conical spines up to 1.5 µm long.

Receptacula ad 60 x 4 mm, simplicia, solitaria vel gregaria, caesia, murina. Hyphis efibulatis; basidiis fibulatis. Sporis ellipsoideis, echinulatis, ut in oratione infra.

Again, spore ornamentation provides a most confusing situation. Clavaria ardosiaca not only shares almost identical fruit bodies (colour, stature, etc.) but unusually large spores, however, its spores are smooth. At the same time, C. musculo-spinosa specimens vary greatly in this character, for TENN no. 43541 and Horak's collections show almost no smooth spores, whereas TENN no. 43540 shows very few ornamented spores. Were the rough spores not seen on TENN no. 43541, it would surely have been accessioned under C. ardosiaca. Thus, although it would appear that species pairs exist - one with ornamented spores, the other with smooth-this maybe artifactual, really representing a cline under unknown controls.
The wide, long basidia are a reflection of the large spores. Sterigmata number is very variable, perhaps (as in many other taxa) related to the unusual variation in spore dimensions and E values. Sterigmata are blunt until near maturity.