Fruit bodies up to 90 x 3 mm, simple clubs, cylindrical, scattered to gregarious, arising from small whitish mycelial patches. Club ivory to pale greenish yellow (off-white to "pale olive-buff"), opaque, appearing waxy; equal to tapering slightly upward; flesh concolourous. Stipe up to 40 x 2 mm, shining-silky, off-white, equal.
Tramal hyphae inflated, long-celled, thin-walled, clampless, parallel, tightly packed, free to adherent; secondary septa common; crystalline material deposited among tramal hyphae. Subhymenium poorly developed, pseudoparenchymatous. Hymenium hardly thickened; basidia (Fig. 35) 30-35 µm long, clavate, narrow and attenuate below, clamped; contents multiguttulate at maturity; sterigmata 2, long, stout, somewhat divergent, straight.
Spores (Fig. 36) 8.6-10.8 x 6.5-7.6 µm (E = 1.19-1.67; E^m = 1.40; L^m = 9.84 µm), subglobose to broadly ellipsoid, smooth, thin-walled; contents opalescent; hilar appendix prominent, broad, papillate.

North Island: WKR, across river from Forestry Headquarters, 24.vi.81, coll. RHP, no. 42411 (holotype, PDD; isotype, TENN), 42428 (TENN); WKR, 24.vi.81, coll. EH, s.n. (ZT); WKR, vic. Forestry Headquarters, 25.vi.81, coll. RHP, no. 43667 (TENN). South Island: FGNP, Rd to Gillespie's Beach, 9.v.82, coll. RHP, no. 43565 (TENN).

On leaf humus and very rotten, soggy wood.

Receptacula ad 90 x 3 mm, simplicia, gregaria, pallide olivacea. Hyphis efibulatis; basidiis fibulatis, 2-sterigmatibus. Sporis subglobosis vel late ellipsoideis, laevibus, ut in oratione infra.

corner (1970) included four taxa with white fruit bodies and broad spores in subg. Holocoryne. None is 2-sterigmate, and I can find no other report of such a fungus in the literature on Pacific taxa.
This and Clavaria subsordida were placed under a single taxonomic designation based on fruit body morphology, for they are extremely similar macroscopically. Closer examination revealed that C. ypsilonidia produced ellipsoid spores and strictly 2-spored basidia, immediately separating it from C. subsordida. Also, both taxa are similar in fruit body colour and stature to C. echino-olivacea, which produces spiny spores. Care must be taken to distinguish these three taxa.
Basidia in Clavaria ypsilonidia are short (not more than 50 µm long by hymenial measurements) and somewhat agglutinated, obscuring the basal loop-like clamp. The basidia of C. subsordida are virtually free (not agglutinated) and the clamp - or bifurcate basidial base - is easily observed.
Fruit bodies of the species vary in colour from virtually pure white (which I originally designated a separate species) to pallid olive-buff, sometimes with the club pigmented but not the stipe. This colour variation appears irregular, however, and unaccompanied by micro morphological variation, so I consider that no separate taxa are warranted.