Type: Caulicolous Fungi; Description: Basidiomata perennial, effused, forming irregular patches 60–100 × 30–40 mm. Pore surface white or pallid cream, even, later deeply creviced, margin abruptly thinning out, concolorous. Context white, up to 600 μm thick. Hyphal system dimitic. Metuloids abundant, gloeocystidia present. Cystidia encrusted, 30–45 × 7–10 μm, hyaline. Basidiospores subglobose to ellipsoid, 6–9 × 6–7 μm, echinulate, amyloid.

Distribution: Northland, Auckland, Bay of Plenty, Taranaki, Taupo, Rangitikei, Wanganui, Wellington, Wairarapa, Buller, Westland, Marlborough, Dunedin.; 1st Record: Cunningham (1955).

Significance: Causes root rot and stem canker that results in group mortality over restricted areas. It is often already established in small areas of indigenous scrub vegetation (mainly Leptospermum scoparium) present before exotic trees are planted. Infection of planted trees occurs when a root or part of the stem comes in contact with infected roots or twigs of the scrub plants. Leptospermum scoparium, Pteridium esculentum, and Rubus fruticosus often act in this way as transmission agents. As the disease progresses a girdling canker develops at the root collar or on the stem, and copious resin bleeding occurs. Infected trees die slowly over a period of 3–4 years and roughly circular patches of dead vegetation are a distinctive feature of the disease. In most parts of New Zealand, incidence of the disease is low and losses are insignificant. In three Northland forests and one forest in Marlborough where the fungus is widespread, 10–20% mortality was reported within 10 years of establishment (Dick 1983).; Host(s): Parasitic attack: Brachyglottis repanda, Chamaecyparis lawsoniana, Coprosma grandifolia, Cupressus macrocarpa, Cytisus scoparius, Dendrobenthamia capitata, Eucalyptus botryoides, E. ovata, E. saligna, Hakea sericea, Hebe sp., Leptospermum scoparium, Macropiper excelsum, Pinus caribaea, P. contorta, P. elliottii, P. muricata, P. nigra subsp. laricio, P. palustris, P. patula, P. pinaster, P. radiata, P. taeda, Podocarpus totara, Pomaderris kumeraho, P. phylicifolia, Prumnopitys ferruginea, Prunus armeniaca, P. avium, P. cerasifera, P. persica, Pseudopanax arboreus, Pseudotsuga menziesii, Pyrus communis, Rosa rubiginosa, Thuja plicata, Ulex europaeus. Non-parasitic attack: Acacia dealbata, Ageratina adenophora, Beilschmiedia tawa, Fuchsia excorticata, Kunzea ericoides, Leucopogon fasciculatus, Malus ×domestica, Melicytus ramiflorus, Meryta sinclairii, Muehlenbeckia australis, Passiflora tetrandra, Pteridium esculentum, Quintinia serrata, Ripogonum scandens, Rubus australis, R. fruticosus agg., Schefflera digitata, Tecomaria capensis, Weinmannia racemosa.

Hyphae hyaline, thin-walled, 2-3.5 µm wide, septa without clamps. Gloeocystidia present but sometimes rare, acute, 20-40 x 4-6 µm, some weakly sulphobenzaldehyde-positive. Cystidia hyaline, thin- to slightly thick-walled, encrusted and then 30-45(-50) x 7-10(-15) µm, dextrinoid; cystidia fusiform and up to 6.5 µm wide without crystals. Basidia hyaline, thin-walled, clavate to urniform, 25-35 x 6.5-8 µm, (basal swelling up to 9 µm wide), with four sterigmata up to 8 µm long. Spores hyaline, thin-walled, subglobose to ellipsoid, often collapsed 7.5-9.5 x (5.3-)6-7.5 µm, echinulate, amyloid, appearing more or less smooth in KOH.

This description differs from that by Cunningham (1955, 1963) in reporting the presence of gloeocystidia and describing the basidiospores as amyloid and echinulate. The weakly sulphobenzaldehyde-positive reaction of gloeocystidia in the type specimen need not be characteristic of the species. The reaction to sulphobenzaldehyde is often indistinct in herbarium material as it depends on both age and method of preservation. It should be tested on fresh material.
The species is closely related to Gloeocystidiellum convolvens (Karsten) Donk, which also has encrusted cystidia, gloeocystidia, simple-septate hyphae and echinulate, amyloid spores. Gloeocystidiellum sacratum differs in the smooth hymenophore (only an occasional wart present), the scarce and small gloeocystidia, and larger basidia and basidiospores. For these reasons a new combination in Gloeocystidiellum Donk is proposed. The alternative would be a new genus for both species.
Burdsall (1985) placed the species in Amylostereum Boidin, because of "the hyaline, simple-septate hyphae, subulate reddish-brown pseudocystidia and amyloid spores with a granulose surface". This is rather surprising as all species of Amylostereum so far described have smooth, cylindrical basidiospores and clamps at all septa; most of them also possess thick-walled, brown basal hyphae. Gloeocystidiellum sacratum has hyaline cystidia, which become reddish brown in Melzer's reagent. Moreover the presence of gloeocystidia, noted by Taylor (1969), is not a typical character of Amylostereum. Finally, cultures of G. sacratum (CBS 796.86) display occasional septa with 1-3 clamps, a character known in Gloeocystidiellum (Boidin 1966), but not in Amylostereum.

Holotype: on Leptospermum scoparium J.R. & G. Forst., New Zealand, Waikato, Kawhia Harbour, coast, coll. J.D. Atkinson, Jan. 1953 (PDD 11845).