Collections:
New Zealand. With Euantennaria pacifica, (1,2) on Hebe stricta var. egmontiana, Auckland Province, Pureora, 21 Mar 1963, (1) S. J. Hughes, DAOM 96080b, (2) R. Zondag, DAOM 96083c; (3) on Leptospermum ericoides, Auckland Province, Hatepe, near Lake Taupo, 4 Mar 1963, S. J. H. and J. M. Dingley, DAOM 96064d; (4) on Melicope simplex, Canterbury Province, Price's Bush, near Little River, Banks Peninsula, 13 May 1963, S. J. H., DAOM 96068a; (5) on Myrsine australis, Auckland Province, Hunua Gorge, Hunua, 12 Feb 1963, J. M. D., PDD 20549 (DAOM 96086) (Euantennaria mucronata also present); (6) on Neomyrtus pedunculata, Nelson Province, Waimea, Eve's Bush, 1 Mar 1967, J. M. D., FDD 25894 (DAOM 117160b); (7) on Shawia paniculata. North Canterbury, Ashley Gorge, 14 May 1963, J. M. D., DAOM 96075c (FDD 36103). With Euantennaria caulicola, (8) on Alseuosmia macrophylla, Wellington Province, Tongariro National Park, Erua, 6 Mar 1963, S. J. H., DAOM 93391c (Acrogenotheca elegans and Metacapnodium moniliforme also present) ;(9) on Coprosma tenuifolia, Auckland Province, Pureora, 21 Mar 1963 S. J. H., DAOM 93420a (Trichopeltheca asiatica, Enthallopycnidium, and Tripospermum also present); (10) on Gleichenia cunninghami, Wellington Province, Horopito, 8 Mar 1963, S. J. H., DAOM 93416c. With Euantennaria novae-zelandiae, (II) on Coprosma sp., North Canterbury, Ashley Gorge, 14 May 1963, S. J. H., DAOM 96062a; (12) on Leptospermum ericoides, Auckland Province, Hatepe, near Lake Taupo, S. J. H. and J. M. D., DAOM 96064b. With Euantennaria mucronata, (13) on Nothofagus sp., Auckland Province, Waimauku, May 1963, Mr O'Shea, DAOM 96071b. With Acrogenotheca elegans, (14) on Neopanax arboreum, Auckland Province, Pureora, 21 Mar 1963, S. J. H., DAOM 97056b.
New Zealand collections in Herb. K: (15) 'Antennaria scoriadea, Berk. [scr. Berkeley] Colenso 4697, New Zealand [scr. Colenso]' (Janetia capnophila associated with Euantennaria mucronata)', (16) 'Antennaria scoriadea B. [ser. Berkeley] 2852. 3632. 3644 [scr. ?Colenso]' (J. capnophila with E. mucronata), (17) 'Antennaria Robinsonii. New Zealand. M. C. Cooke, May '86 [scr. M. C. Cooke]. 298. Leaves of Drimys and Hedycarya infested with a Lecanium, the latter parasitised by a Chalcid or other insect, and both insects infested by a fungus. Near Wellington. T. Kirk [scr. presumably T. Kirk]' (J. capnophila with Metacapnodium moniliforme, Tripospermum, and other sooty moulds).
Australia. (18) with Euantennaria pacifica on Acacia melanoxylon, Gorae, Portland, Victoria, 31 Mar 1962, A. C. Beauglehole (5242), DAOM 96060b; (19) with Euantennaria pacifica and E. mucronata, on the type collection of Podosporium grande in K, 'on Aster argophyllus [Olearia argophylla] stems, Fatigue Range, Gipps Land [Victoria], Australia. Turton [scr. M. C. Cooke]'.

Colonies effuse, black, associated with sooty moulds especially with species of Euantennaria and their synanamorphs and also with Acrogenotheca elegans. Mycelium superficial, composed of smooth to minutely roughened, cylindrical, branched (usually at right angles), subhyaline to brown hyphae 3.5-6.0(-7.2) µm wide, and septate at 9-23 µm intervals. Hyphae form a thin,' sparse, and irregular network on leaf surfaces but when associated with spongy, loosely or densely plumose, or compact euantennariaceous subicula the hyphae may be so abundant as to conceal the supporting hyphae of the associated fungus and extend beyond them. Hyphae can also creep up the tall, arborescent conidiophores and setae of Acrogenotheca elegans. Conidiophores micronematous, mononematous, or fasciculate. Conidiogenous cells integrated, intercalary, scattered or formed in a series in up to 12 successive hyphal cells. They are brown to dark brown, monoblastic, inflated to 8-11 µm wide (when viewed from above) with a single cylindrical to conico-truncate denticle, 5-9 µm long with a flat scar 3.6-5.4 µm wide. The denticle is usually more deeply pigmented than the rest of the cell. Conidia straight to slightly curved, occasionally bent, narrowly obclavate, rounded at the apex which is 3.5-5.5 µm wide, conico-truncate at the base, (7-)9-13(-16)-septate, thick-walled, dry, pale brown to brown, occasionally darker with age and then slightly constricted at the septa. The basal cell is cylindrical to conico-truncate, 7.5-12.5 µm long and dark brown, usually conspicuously darker than the other cells. Conidia measure (58-)80-125(-145) x 10.8-13.5(-16.2) µm. Secession is schizolytic. Conidia germinate readily at the apex to produce a hypha and frequently anastomose, one with another. Up to 7 cells of a conidium may become modified into brown to dark brown conidiogenous cells and these produce conidia. Conidium septation is acropetal.

Associated with sooty moulds, particularly with species of Euantennaria and Acrogenotheca elegans. New Zealand and Australia (Victoria).

Coloniae effusae, atrae. Mycelium superficiale, reticulatus vel fasciculatus, ex hyphis levis vel minute verruculosis, cylindricis, ramosis, subhyalinis vel pallide brunneis, 3.5-6(-7.2) µm crass., septatis. Conidiophora micronemata, mononemata, repentia vel erecta fasciculataque. Cellulae conidiogenae in conidiophoris incorporatae, plerumque intercalares, 8-11 µm lat., brunneae et unidenticulatae. Denticuli atrobrunnei, cylindrici vel conico-truncati, 5-9 µm long., cicatrice planis 3.6-5.4 µm lat. praediti. Conidia solitaria, sicca, recta vel curvata, auguste obclavata, (7-)9-13(-16)-septata, (58-)80-125(-145) x 10.8-13.5(-16.2) µm, crasso-tunicata, pallide brunnea vel brunnea, apicem versus pallidiore et 3.5-5 µm crass. Cellula basali cylindrica vel conico-truncata, 7.5-12.5 µm long., atrobrunnea. Conidia schizolytice secedentia.
Habitat: In socio coloniis plerumque Euantennariae pacificae, E. mucronatae, E. caulicola, E. novae-zelandiae et Acrogenothecae elegantis in foliis, ramis ramulisque. Nova Zelandia et Australia.
Typus: In socio coloniis Euantennariae pacificae in ramulis Shawiae paniculatae, 'North Canterbury, Ashley Gorge', Nova Zelandia, 14 Maji 1963, J. M. Dingley, DAOM 96075c (holotypus), PDD 36103 (isotypus).

No evidence was seen of parasitism by Janetia capnophila on any sooty mould(s) with which it is associated so I conclude that the fungus is a mycophile. It is, furthermore, so restricted in its choice of associates that it may be called a capnophile.
The taxonomic position of J. capnophila presents a problem because some congeneric species have been classified in Sporidesmium and Janetia. The more or less obclavate conidia produced on superficial conidiogenous cells are also reminiscent of those of Clasterosporium. Species of Clasterosporium, however, have hyphopodiate hyphae so this name is not considered further.
Several species described in or transferred to Sporidesmium occur on leaf surfaces. Some of these have superficial mycelium and broadly flask-shaped, deeply pigmented conidiogenous cells incorporated in the hyphae, and these have been reported as monoblastic, e.g., S. bonarii M. B. Ellis (1958), S. garryae Bonar (1965), and S. lagenocarpi M. B. Ellis (1963): and last named has setae on the mycelium. In some others of a similar nature the conidiogenous cells are somewhat longer, e.g., the 'Sporidesmium" anamorph of Eupelte rapaneae Hansf. (M. B. Ellis 1958), S. bombacis M. B. Ellis (1958), and S. baccharidis (Sydow) M. B. Ellis (1961).
Sporidesmium is predominantly a genus of species which occur on wood and bark, with immersed mycelium bearing macronematous conidiophores which proliferate per currently to produce a succession of conidia. I believe the foliicolous species with monoblastic conidiogenous cells need to be segregated.
In 1976 M. B. Ellis proposed the name Janetia for species with superficial hyphae and Sporidesmium-like conidia produced on intercalary, polyblastic, denticulate conidiogenous cells. The type species, J. euphorbiae M. B. Ellis was described on stems of Euphorbia tirucalli from Tanzania. Conidiogenous cells are l-3(-5)-denticulate in the type collection (IMI 163941): conidia are 18-36(28) x 6-8(6.7) µm (tide M. B. Ellis).
In Janetia faureae (Pirozynski) M. B. Ellis (1976) (isotype in DAOM 133968), on leaves of Faurea saligna from Tanzania, the conidiogenous cells are 1- or 2(-3)-denticulate and the conidia 50-120 x 4-4.5 µm (fide M. B. Ellis).
Janetia bacilliformis Gamundi, Arambarri, et Giaiotti (in Gamundi et al. 1979) was described on leaves of Nothofagus dombeyi from Argentina. Conidiogenous cells were described as generally monoblastic, but they can be 2-blastic. Conidia are robust and '60-156 x 5-7.8(-9) µm.
A fourth species of Janetia, J. mangiferae Hughes et Cavalcanti (1983) has been described from Brasil, on leaves and smooth stems of Mangifera indica. This species is close to J. euphorbiae but has shorter and narrower (l-)2-4(-5)-septate conidia measuring 8.5-23 x 4.5-5.2(-6) µm, produced on polyblastic conidiogenous cells which bear up to 6 denticles. Conidium cells can function as monoblastic conidiogenous cells.