Fruit bodies of indeterminate length, less than 1 mm thick, as more or less erect extensions of sterile rhizomorphs. Rhizomorphs beige, tan or pallid ochre, silky, equal, sterile, fertile areas indistinguishable, ascending. Taste and odour not recorded. Tramal hyphae 5-14 pm diam., hyaline, thin- to slightly thick-walled (wall up to 0.5 gm thick), unclamped, strictly parallel, adherent. Subhymenium extensive; hyphae 2-3 gm diam., unclamped, hyaline, tortuous. Hymenium thickening, agglutinated; basidia 30-35 x 7-9 gm, broadly clavate, unclamped; contents homogeneous; sterigmata 4, extremely stout, inflated proximally, abruptly narrowing distally. Caulocystidia (Figs 73, 74) of two types: (i) 15-25 x 6-7 gym, curved-clavate, thick-walled; (ii) up to 350 p.m long, thick-walled and somewhat inflated below, narrowing distally to a filiform tip.

Spores (Fig. 75) 6.8-8.3 x 2.9-3.2 gm (E = 2.22-2.75; E'" = 2.48; L- = 7.38 gm), cylindrical to narrowly reniform, hyaline, thin-walled; contents homogeneous; hilar appendix gradual, broad.

For years I have observed (and sometimes collected) tangles of rhizomorphs with erect (and therefore clavarioid) ends, only to find them consistently sterile. Now I find several collections with rare fertile hymenium. Tramal structure, caulocystidia, and general habit match Macrotyphula very well, and may have been figured by Corner (1950, text fig. 103, right side, under Clavariadelphus junceus). Differences between M. rhizomorpha and the M. junceus (or M. defibulata) complex are so numerous that I have no hesitation in proposing a new species.

Apparently included in the hymenium are many conidiophores, but I cannot distinguish them. My conclusion is based on abundant conidia, similar to basidiospores (but small), which are freed in squash mounts. The short, clavate caulocystidia must elongate into the longer, tapering type, which vary greatly in length, but I have not seen short, obviously intermediate forms. Caulocystidia in M. rhizomorpha are similar to those of M. defibulata, and somewhat longer than those described by Berthier (1976) for European M. juncea.