A. limonea is larger than A. novae-zelandiae, the cap yellowish in colour, with well-developed darker scales.

Type: Radicicolous Fungi; Description: Basidiomata pileate, centrally stipitate. Pileus 80–130 mm in diameter, lemon yellow, with dark brown tufted scales sprinkled thickly at centre and more sparsely towards the margin, convex at first, becoming almost plane later, dry; flesh firm, white. Gills sinuately decurrent, moderately crowded, creamy white, becoming pinkish fawn. Stipe tapering towards the pileus, with a bulbous base, light brown above a substantial floccose annulus, shading to brown or olive green below, velutinate, solid, 100–150 mm long. Basidiospores ovoid, 7–8 × 5–7 m, non-amyloid; spore print white.

Distribution: See Significance.; 1st Record: Stevenson (1964: as Armillariella limonea).

Significance: In older records (Gilmour 1966a; Dingley 1969), Armillaria limonea and A. novaezelandiae were collectively referred to as Armillaria mellea, a European species not known from New Zealand. Most records of disease attributed to infection by Armillaria (clearly recognisable from the presence of rhizomorphs and fan-like mycelial sheets under bark) do not identify the species as it is not possible to do so in the absence of fruiting bodies. No distinction between the two species is made in the account that follows. Shaw et al. (1981) found no significant difference between them in terms of pathogenicity. Hood & Sandberg (1993), using a large number of isolates in pot tests, found that A. limonea was generally slightly less pathogenic to Pinus radiata than A. novaezelandiae. They also found considerable variability in pathogenicity between different isolates of the same species. Armillaria limonea and A. novaezelandiae are endemic in New Zealand, fruiting bodies and rhizomorphs of both species being common in indigenous forests. They are apparently unable to parasitise roots in podocarp/hardwood forests where there is no evidence of mortality caused by Armillaria spp. Parasitic attack has been reported in Nothofagus forests (Rawlings 1953). As the natural distribution of Armillaria spp. is restricted to forested areas, root disease caused by these species is a first rotation problem only in plantations established on former indigenous forest sites. In new Pinus radiata plantations established on such sites, mortality commences 3–6 months after planting and up to 10% of the trees may be killed in the first year. Mortality continues for about 10 years and may affect up to 50% over this period (Shaw & Calderon 1977). Trees older than 10 years are rarely killed but infection persists in a non-lethal, chronic form to the end of the rotation. From a country-wide survey, Self et al. (1998) found that 39% of plantation trees on formerly indigenous forest sites were chronically infected. Such trees are susceptible to windthrow and toppling and grow more slowly than uninfected trees. Estimates of volume loss attributable to Armillaria infection vary between 14–24% for individual trees (Shaw & Toes 1977) and 6–13% for a 28-year sawlog regime (MacKenzie 1987). Armillaria root disease is not a problem in first rotation Pinus radiata stands established on farmland or other sites that previously carried only herbaceous cover (Gilmour 1966a). Self et al. (1998) found that 4% of trees planted on herbaceous shrub sites were infected by Armillaria spp. There is considerable evidence to show that on such sites, stumps left when the first tree plantation crop is felled can be infected by basidiospores carried over long distances (Hood, Horner et al. 2002). Rhizomorphs are not produced for several years and thus there is little or no mortality in the second rotation crop. When rhizomorph production does occur, trees are older and have developed some resistance. Although there is no mortality, varying numbers of trees become chronically infected and there is a consequent loss of volume increment. Kimberley et al. (2002) estimated a volume loss of just over 2% in a 13-year-old second rotation stand where approximately 20% of trees carried non-lethal, chronic infection. The only proven eradicative control measure for armillaria root disease is the removal of stumps, which are the main source of inoculum (van der Pas & Hood 1984). Stumping is expensive and difficult to undertake on steep country and is rarely practiced. Application of fungicides to stumps or soil has not been effective (Shaw et al. 1980; van der Pas & Hood 1984). Inoculation of stumps with saprobic fungi immediately after felling to prevent colonisation by Armillaria spp. (Yang & Hood 1992) is being explored. ADDITIONAL REFERENCES: Hood (1989: review of armillaria root disease in New Zealand); van der Kamp & Hood (2002: infection process); Hood, Kimberley et al. (2002: influence of silviculture); Hood & Kimberley (2002: disease survey methods); Firth & Brownlie (2002: aerial disease assessment methods); Shaw & Kile 1991 (comprehensive world-wide review of species Armillaria and armillaria root disease).; Host(s): Beilschmiedia tawa, Dacrydium cupressinum, Hedycarya arborea, Knightia excelsa, Metrosideros robusta, Nothofagus menziesii, Nothofagus sp., Pinus radiata.

[Notes from Kew Type specimen, PRJ 2010] Kew images.

Pileus 8-13 cm diam., lemon yellow, sprinkled thickly at centre and more sparsely towards the margin with dark brown, tufted scales, dry, convex at first with strongly down-rolled margin, becoming almost plane with a waved edge; flesh firm, white. Gills sinuately decurrent, moderately crowded, creamy white becoming stained pinkish fawn. Stipe 10-15 x 1-1.5 cm, light brown above substantial floccose ring, shading to brown or olive green below, velutinate, sometimes with a few tufted scales, solid, tough, slightly bulbous at base. Spores 7-8 x 5-6.5 µm, non-amyloid, moderately thick-walled (Fig. 25); print white.

In dense groups round standing dead Nothofagus, Butterfly, Wellington, 22.5.1949. Stevenson (type); Nelson, 6.6.1955, E. Cannington; Eve's Valley, Nelson, 10.5.1957, Stevenson.

Pileus 8-13 cm diam., limoneo-luteus, medio dense, marginem versus sparsius squamis fusco-brunneis crinitis sparsus, siccus, primum convexus margine valde deflexo-revoluto, deinde fere planus margine undulato; carne firma alba. Lamellae sinuato-decurrentes, modice confertae, cremeo-albae deinde puniceo-fulvotinctae. Stipes 10-15 x 1-5 cm, supra annulum satis validum floccosum laete brunneus, inferne magis magisque brunneus vel olivaceus, velutinatus, interdum squamis paucis crinitis praeditus, solidus, tenax, basi leviter bulbosus. Sporae 7-8 x 5-6.5 µm, haud amyloideae, parietibus modice crassis; in cumulo albae.

This common tree-destroying fungus with very characteristic bootlace rhizomorphs is regularly seen in plantations. In Japan it is recognized as the mycorrhizal fungus of the saprophytic orchid Gastrodia R. Br., one species of which is fairly common throughout New Zealand.