Ectolechiaceae was
circumscribed by
Alexander Zahlbruckner in
Adolf Engler's influential 1905 work
Die Natürlichen Pflanzenfamilien. Zahlbruckner defined the family around small, crust-forming lichens with a single-celled
green alga as the partner (then referred to as
Protococcus), and described them as producing tiny, round
apothecia that begin sunken in the thallus and later sit on the surface, usually without a well-developed margin. He noted that the may be flat to shallowly cup-shaped and either exposed from the start or temporarily covered when young by a thin skin that later tears away, and he characterised the internal tissues by well-developed
paraphyses and
asci bearing one to eight colourless spores ranging from simply
septate to strongly multi-septate () forms. In his treatment the family was confined to
tropical, leaf-dwelling lichens (including those on fern
fronds), and he subdivided it into several genera on the basis of spore form, paraphysis structure, and whether algal cells occur in the upper or lower apothecial layers, recognising groups such as
Asterothyrium,
Lopadiopsis,
Sporopodium,
Lecaniella,
Arthotheliopsis, and
Actinoplaca. The family name
Ectolechiaceae is based on the generic name
Ectolechia, which has largely fallen out of use in modern classifications. Current treatments instead apply the relevant generic names (such as
Sporopodium) to the ectolechiaceous lineage discussed in recent phylogenetic work. In older classification systems, the mainly tropical, leaf-dwelling (
foliicolous) genera now treated in this family were often separated from largely temperate
crustose lineages such as
Micarea, which was commonly treated as the
type genus of a separate family, Micareaceae.
Morphological comparisons in the late 20th century and early
molecular studies both questioned whether those family boundaries reflected evolutionary history, and proposed that the foliicolous "pilocarpaceous" element and the micareoid
Micarea lineage belong to a single broader family concept. Using mitochondrial small-subunit
rDNA data, Andersen and Ekman concluded that
Micarea (in its traditional sense) does not remain a single lineage unless the predominantly foliicolous taxa traditionally treated in Pilocarpaceae/Ectolechiaceae are included, and they therefore treated Micareaceae and Ectolechiaceae as
synonyms within an expanded family. On nomenclatural grounds they argued that the correct name for that expanded family would be Pilocarpaceae, because Pilocarpaceae and Ectolechiaceae were both published in 1905 whereas Micareaceae was introduced later. That name choice is not followed under current nomenclature because Pilocarpaceae is an illegitimate later
homonym of Pilocarpaceae . Recent treatments therefore use
Ectolechiaceae as the correct family name for the clade historically discussed under Pilocarpaceae, and regard Byssolomataceae (used in some databases) as a later synonym. In analyses using multiple
genetic loci, a mainly tropical, foliicolous assemblage (often discussed as Ectolechiaceae
sensu stricto and including genera such as
Byssoloma,
Calopadia,
Fellhanera,
Lasioloma and
Sporopodium) is recovered as distinct from the
temperate-to-
arctic lineages centred on
Micarea (including
Helocarpon), clarifying why single-locus trees previously produced contradictory "family" signals. ==Description==