The family is classified as incertae sedis with respect to ordinal placement in the class Lecanoromycetidae, as there is no reliable molecular data available to establish phylogenetic relationships with similar taxa.[4]
Joseph Hafellner in 1984 described a new monotypic family, Helocarpaceae to contain the genus Helocarpon.[1][7] Then Eriksson et al in 2004, placed Helocarpon as a genus within the Micareaceae family,[8] along with genera; Micarea, Psilolechia, Roccellinastrum and Scutula.[9]
In 2005, molecular phylogeny based on mitochondrial rDNA sequences showed that the genus was not related to the Micareaceae family.[10]Helocarpaceae was re-instated to hold the genus Helocarpon.[11]
The genera are generally distinguished by a crustose thallus and chlorococcoid photobiont (relating to green algae of the genus Chlorococcum). They are usually immarginate (not having a distinctive margin or border) and convex biatorine apothecia. When the margin of the spore body is pale or colorless, it is called 'biatorine'. They also have a poorly developed proper exciple (margin), simple or sparsely branched to abundantly branched and anastomosed (connected) paraphyses (the erect sterile filaments often occurring among the reproductive organs).[10] The asci has an apical cushion surrounded by a tube-structure,[17] colourless and simple (ellipsoid or tear-shaped) to transversely septate asco-spores which are lacking perispore (outer covering of a spore). They have immersed (surrounded), sessile or stalked pycnidia (asexual fruiting body), and an abundance of conidial types.[10]
^Eriksson, O. E.; Baral, H.-O.; Currah, R. S.; Hansen, K.; Kurtzman, C. P.; Rambold, G.; Laessøe, T. (2004). "Outline of Ascomycota – 2004". Myconet. 10: 1–99.
^ abcAndersen, Heidi L.; Ekman, Stefan (January 2005). "Disintegration of the Micareaceae (lichenized Ascomycota ): molecular phylogeny based on mitochondrial rDNA sequences". Mycol. Res. 109 (1). The British Mycological Society: 21–30. doi:10.1017/S0953756204001625.
^Lücking, R.,; Hodkinson, B.P.; Leavitt, S.D. (2016). "The 2016 classification of lichenized fungi in the Ascomycota and Basidiomycota – Approaching one thousand genera". The Bryologist. 119 (4): 361–416. doi:10.1639/0007-2745-119.4.361.((cite journal)): CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
^Cannon PF, Kirk PM (2007). Fungal Families of the World. Wallingford: CABI. p. 36. ISBN0-85199-827-5.
^ abBeauchamp, Hélène; Vust, Mathias; Clerc, Philippe (2007). "Notes on selected terricolous crustaceous lichens of Switzerland: Distributional, ecological and Red List data". Herzogia. 20: 115–144.