Subiculum persistent, dark brown, wiry, partially without stromata but with many synnemata. Stromata (1050)1160 ± 125(1375) µm high, (1125)1245 ± 99(1300) µm wide (n = 5), globose, with a short broad cylindrical base, copper brown, black around the ostioles, with rugose to wrinkled surfaces, solitary to crowed, becoming laterallycompressed. Ostioles coarsely papillate. Ectostroma 75-100 µm thick, black, hard, splintering. Entostroma cream, later dark brown, confined to base, absent in mature material. Perithecia detached and collapsed in mature material. Ascus apical rings (6.7)7.3 ± 0.5(7.6) µm long, upper width 4.5-5 µm, lower width 3.5-4 µm (n = 5), J+, dark blue. Ascospores (21.6)23.3 ± 1.4(26.9) µm long, (6.7)7.7 ± 0.5(8.6) µm wide (n = 30), inequilaterally ellipsoidal, brown to dark brown, with 10-13 µm long straight germ slit centred on the flat side, both extremities and the flat side surrounded by a slimy sheath, up to 4.5 x 3-4 µm thick at the ends, 1 µm thick at side.
Synnemata up to 650 µm high. Conidia 6-10 x 3-4 µm.
ANAMORPH: Dematophora.

HOST: Undetermined hardwood.
MATRIX: Decorticated wood.

Subiculum perdurans, atrobrunneum, filo metallico simile, stromata orbum sed multis synnematibus praeditum. Stromata (1050)1160 ± 125(1375) µm alta, (1125)1245 ± 99(1300) µm lata, globosa, basi lata brevicylindricaque, cupreobrunnea, ostiola circa nigra, superficie rugosa ad corrugata, solitaria ad gregaria lateraliter compressa. Ostiola grosse papillata. Annulus apicalis asci (6.7)7.3 ± 0.5(7.6) µm altus, parte superiore 4.5-5 µm et inferiore 3.5- 4 µm latus, iodo valde coerulescenti. Ascosporae (21.6)23.3 ± 1.4(26.9) µm longae, (6.7)7.7 ± 0.5(8.6) µm latae, asymmetrice ellipsoideae, brunneae ad atrobrunneae, fissura germinativa recta 10-13 µm longa in regione centrali partis planae ascosporae locata praeditae, apicibus parteque plana vagina mucosa 4.5 x 3-4 µm ad apices et 1 µm ad latus crassa circumdatis. Status anamorphosis Dematophora.

ETYMOLOGY: In honour of the mycologist G. Samuels who collected and cultured many of the Rosellinia specimens deposited at PDD.
NOTES: Rosellinia samuelsii combines characters of massive stromata, flattened, ellipsoidal ascospores with a short germ slit and a Dematophora anamorph. Many fertile synnemata are present in parts of the subiculum devoid of stromata.
Rosellinia samuelsii differs from R. hughesii by its larger stromata and larger ascospores with a short germ slit, and from R. buxi by a thinner ectostroma, larger ascus apical rings, ascospores surrounded partially by a slimy sheath and shorter germ slits, as well as larger conidia (Petrini 1993). Rosellinia paraguayensis Starbäck and R. petrakii Narendra have similarly shaped but larger ascospores than R. samuelsii. Rosellinia paraguayensis has also a Dematophora anamorph, in contrast to R. petrakii.
Rosellinia britannica has ascospores of similar size, but it differs from R. samuelsii by the smaller stromata of a different shape, an evanescent subiculum with a Geniculosporium anamorph, and ascospores with a longer germ slit (Petrini et al. 1989).

HOLOTYPUS (hic designatus): New Zealand, North Island, Auckland, Waitakere Ranges, Huia, Parau Tr., on decorticated wood, 23 Oct 1980, G. J. Samuels & P. R. Johnston, PDD 49690.