Colonies hypophyllous, scattered, angular, 1.5-5 mm long and 1-2.5 mm wide, marginally grey-brown with central, black, superficial, continuous or discontinuous stromatic crusts bearing sessile, erect phialides and ascomata. The upper surface of the host leaves bears reddish-brown areas, which correspond closely to the hypophyllous colonies. Invasion of leaf tissues is accomplished initially by the production of ingress cells on germ tubes produced from ascospores. Such cells are ellipsoidal and expand to fill suprastomatal chambers, and from each a hypha extends further into the mesophyll to produce cylindrical, smooth, brown to pale brown, irregularly branched, intercellular hyphae 4-8 µm wide and septate at 12-36 µm intervals. Hyphae also penetrate between cells of the 2-layered palisade where they produce more or less parallel branches reaching almost as far as the upper epidermis. Lateral extension of immersed hyphae is apparently restricted by the presence of larger vascular bundles that bear collenchymatous columns extending to the upper and lower epidermis: this presumably accounts for the angular outline of colonies. Immersed hyphae and their branches usually terminate in a single hyphopodium, each of which bears a hyaline pore, c. 1.0 µm diam., indicative of the production of a haustorium: a minute filament has been seen arising at such pores and penetrating the host cell wall, but no swollen end was detected. Hyphopodia in the mesophyll are irregular, mostly ellipsoidal to subglobose to ovoid to obovoid, occasionally angular or lobed, 14-23 x 9-12.6 µm, generally with a short penultimate "stalk cell" 3.5-9 µm long and 3.5-7.2 µm wide. These hyphopodia intergrade with those in the palisade layers, which are longer, generally narrower, more cylindrical, occasionally terminally lobed or short-forked, and 16-31 µm long x 6-9 µm wide. "Stalk cells" of these hyphopodia are narrower and generally longer than those in the mesophyll, being 4.5-12.5 µm long and 3.6-4 µm wide. Within the mesophyll, hyphae form dense knots in the substomatal chambers, and 1 or 2 hyphae derived from these emerge through the stomates to form small stromata on the leaf surface. Stomates are finally ruptured as other hyphae emerge and branch to form a Column up to 35 µm wide connecting the immersed hyphae with the superficial pseudo-parenchymatous stromata; the latter usually coalesce to form a black crust up to 50 µm deep, with inner hyaline layers of cells covered by a single layer of larger cells with their outer wall thick and brown. Phialides (so-called "mucronate hyphopodia" of Meliolaceae) are produced singly or in groups on superficial stromata and occasionally on ascomatal walls. They are erect, straight, or slightly curved away from the leaf surface, flask-shaped, brown to dark brown, 14.5-19 µm long with the venter 7.4-9 µm wide and the neck cylindrical or tapered gradually to 3.4-3.9 µm wide. Phialoconidia are very scanty, but solitary, ellipsoidal, hyaline ones have been seen within the neck, and these are 3.5-4.5 x 1.8-2 µm. Ascomata are often discrete and then subglobose and somewhat flattened with a constricted base seated on the stromatic crust. They are 260-330 µm high, up to 360 µm wide, black, verruculose, and ostiolate. Up to five such ascomata may be formed on a single colony. Walls are up to 90 µm wide with an inner hyaline to subhyaline layer of flattened textura prismatica merging with an outer textura angularis with cells progressively darker brown, larger, and with thicker walls. The outermost layer is composed of subglobose to broadly ellipsoidal to conoid protuberant cells 30-36 µm long and up to 27 µm wide, and often more or less obpyriform with the narrow end c. 7 µm wide. The distal wall of these outer cells is inordinately thickened, up to 7.5 µm, and lamellate. Frequently, 2-4(-5) ascomatal locules occur in a common pulvinate stroma up to 1.2 mm wide. Ostioles are bordered externally by a band of so-called "neck cells" (Luttrell 1989), c. 3.5-6 µm wide, which are more or less cylindrical and distally tapered and brown to very dark brown with a thick, laminated wall at the apex. Vertical sections show that the neck cells merge imperceptibly with the outer cells of the ascoma wall and with the exposed terminal cells of periphyses. Periphyses lining the ostiole are upwardly directed, hyaline, cylindrical, 4-5 µm wide, and merge gradually with paraphyses. Paraphyses are mostly lateral, hyaline, straight or curved, up to 165 µm long, 4.5-5 µm wide toward the base, 5.5-7.2 µm wide at the distal end, and apparently non-septate. Paraphyses that are interspersed amongst asci are scanty and shorter, about 75 µm long. Asci are ellipsoidal, slightly tapered and thin-walled toward the base, very slightly thick-walled in the upper part, unitunicate, 4-spored, 72108 x 30-55 µm. Discharged asci are very thin-walled, longitudinally wrinkled, and 190-205 µm long. Ascospores are broadly ellipsoidal to subcylindrical in face view, 4-septate and slightly constricted at the septa, brown to dark brown, 66.5-73 x 28.5-31.5 µm, with the central cell sometimes longer than the others. In side view, ascospores are somewhat flattened, curved, narrower, 23.4-26 µm wide, with the concave wall hyaline to subhyaline and thinner than the brown to dark brown convex wall. A flattened (?)gelatinous mass appears on the concave side.

Coloniae hypophyllae, angulatae, 1.5-5 mm long. x 1-2.5 mm lat., margine griseo-brunneae, ad centrum atrae. Hyphae germinales, ex ascosporis exorientes, per stomata ingredientes: hyphae immersae ramosae, brunneae, intercellulares, 4-8 µm lat., cellulis 12-36 µm long., hyphopodiis praeditae. Hyphae in mesophyllo irregulariter ramosae sed in vallo saepe parallelae et fere tenus epidermide supera. Hyphopodia in mesophyllo variabilia, ellipsoidea vel subglobosa vel ovoidea vel obovoidea, aliquando angulata vel lobata, 14-23 µm long. x 9-12.6 µm lat. In vallo hyphopodia etiam variabilia sed plerumque angustioria, subcylindrica aliquando ad apicem furcata vel lobata et 16-31 µm long. x 6-9 µm lat. Hyphae immersae per stomatibus egredientes et stromata parva, numerosa, atra, superficialia, coalescentia, ad 50 µm alt. formantes. Phialides in crusta superficiali et interdum in pariete ascomatis, rectae, sessiles, solitariae vel aggregatae, erectae, ampulliformes, brunneae vel atrobrunneae, 14.5-19 µm long., venteri subgloboso 7.4-9 µm lat., collo cylindrico vel apicem versus gradatim angustiore et 3.4-3.9 µm lat. Phialoconidia ellipsoidea, parva, hyalina. Ascomata discreta in crusta superficialia, subglobosa 260-330 µm alt. x ad 360 µm lat., verruculosa, cellulis externis subglobosis vel obpyriformibus, protuberantibus 30-36 µm long. x ad 27 µm lat.. pariete distali incrassato ad c. 5 µm brunneo lamellosoque. Ascomata 2-4(-5), saepe coalescentia in stromate pulvinato, ad 1.2 mm lat. et 350 µm alt., ostiolata. Periphyses superae cellula terminali externa, crasso-tunicata, brunnea. Paraphyses laterales longae, basales breviores. Asci ellipsoidei, unitunicati, 4-spori, apicem versus parum crasso-tunicati, basim versus tenui-tunicati, 72-108 x 30-55 µm. Asci emissi, tenui-tunicati, collapsi, diaphani et longitudinaliter rugosi, 190-205 µm long. Ascosporae late ellipsoideae vel compresso-cylindricae, parum angustiores quam latiores, 4-septatae, ad septa leniter constrictae, curvatae, 66.5-73 µm long. x 28.5-31.5 µm lat. x 23.4-26 µm cr. Paries convexus crasso-tunicatus, brunneus vel atrobrunneus; paries concavus tenue-tunicatus, hyalinus, massa (?)gelatinosa praeditus.
Holotypus in foliis vivis Coprosmae robustae Raoul, Nova Zelandia, Auckland Province, Thames County, Kauaeranga Valley', leg. J. M. Dingley, 16.X1.1965. DAOM 167533. Isotypus in PDD 24806.

Endomeliola is included in Meliolaceae (sensu stricto) because it produces broad superficial hyphae, hyphopodia, phialides, superficial perithecia having protuberant surface cells with distal periclinal walls thickened and lamellate, "neck cells", ostiolar periphyses, paraphyses, unitunicate 4-spored asci, and forcibly discharged, flattened, 4-septate ascospores which germinate bilaterally and from each end cell.
Most of these characters are common to Meliola, Asteridiella, Appendiculella, Irenopsis, and Amazonia, the generic differences being often of degree rather than of kind.
Endomeliola differs from other Meliolaceae in the formation of stomatopodia from which immersed, intercellular, hyphopodiate hyphae arise. Hyphae eventually egress through stomates and produce compound, confluent, superficial stromata in which one or several perithecial locules may develop.
The presence of internal hyphae in Endomeliola should not preclude its inclusion in Meliolaceae. In Asterinaceae, a family which encompasses predominantly superficial, foliicolous ascomycetes, several of these display different degrees and methods of leaf penetration and internal colonisation (Amaud 1918; Hansford 1946; Luttrell 1973).
Coprosma is an Australasian genus of about 90 species: all but one of 45 species are endemic to New Zealand, including C. robusta (Allan 1961) the host of Endomeliola. The only other meliolaceous fungus described on a Coprosma is Asteridiella coprosmae Hansford (1957) from Hawaii; this is totally distinct from Endomeliola.

On living leaves of Coprosma robusta Raoul, New Zealand, Auckland Province, Thames County, Kauaeranga Valley, coil. J. M. Dingley, 16 Nov 1965, PDD 24806 (isotype), DAOM 167533 (holotype).