hapter (noun, pl. hapters, variant spelling: sl. hapteron, pl. hapterons) – an attachment organ formed by the thallus in response to its contact with the substrate; secondarily formed in some fruticose lichens (e. g., Alectoria, Bryoria, Usnea), where a branch may become attached to substrate because of close contact; sometimes also applied to scattered or tufted tiny whitish hair-like structures on the underside of foliose thalli (e. g., in Leptogium), however, this use is confusing and should better be avoided. This is:part of lower thallus surface.