Heterodermia
Heterodermia is a genus of foliose lichens in the family Physciaceae. The genus has a widespread distribution, especially in tropical regions, and contains about 70 species. Heterodermia was historically confused with the related genus Anaptychia, but was distinguished in 1965 based on differences in spore structure and chemical composition. These lichens can be identified in the field using simple chemical spot tests that produce distinctive colour changes when applied to the thallus. The lichens in this genus are small- to medium-sized, usually pale grey in colour, comprising narrow lobes with widened tips fringed with cilia. The lichens can be identified by their thick-walled ascospores and the presence of specific chemical compounds that produce colour reactions when spot tested. Most species are found in tropical and subtropical regions around the world, commonly growing on tree bark in mountain forests. Heterodermia species support a rich community of specialized parasitic fungi, with over 20 different species known to grow specifically on these lichens. Some species have traditional uses in medicine and cooking, particularly in India, Nepal, and Brazil.
Taxonomy
According to Fernanda de Souza and colleagues, the first scientific study of the genus began in 1847 when Thomas Taylor described Parmelia diademata, a lichen that would eventually end up classified as a species of Heterodermia. The genus was formally circumscribed in 1868 by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon. The generic name, which combines the Greek heteros and derma, refers to the presence or absence of a lower cortex.Prior to this classification, Heterodermia species were placed in genus Anaptychia, an idea proposed by Syo Kurokawa in his 1962 monograph on the genus, until some studies showed that the presence of thick-walled spores and the presence of atranorin could be used as characters to separate the genera. In 1965 Josef Poelt split Anaptychia into two genera. Lichens that remained in Anaptychia had thin-walled spores with sculptured surfaces, while those transferred to Heterodermia had thick-walled spores with smooth surfaces. Only nine species remained in the original Anaptychia classification. Although most contemporary lichenologists accepted Poelt's classification, Kurokawa initially rejected these changes in 1973. He later reversed his position and in 1998 accepted Heterodermia as distinct from Anaptychia, transferring several species accordingly.
In North America, members of Heterodermia are colloquially known as fringe lichens or centipede lichens.
Description
Heterodermia typically forms a foliose thallus—occasionally shading towards a somewhat fruticose habit—that is continuous, lobate and irregular, or arranged in loose rosettes across. Neighbouring thalli can merge, producing broad radiating mats or tangled clumps. The lobes may lie separate or touch; they range from closely adnate and appressed to partly ascending and loosely attached, and are linear to linear-cuneate or spoon-shaped. Branching is mostly dichotomous but can be irregular, and the margins are often fringed with cilia that are simple or densely branched.The upper surface is whitish-, grey- or yellow-grey, flat to convex—sometimes concave near the edge—and may be dull or glossy. It can carry isidia, soredia, or, but never pseudocyphellae. The cortex consists of longitudinally aligned hyphae. A is absent. The photobiont forms a continuous band above a well-defined white medulla that may be tinged yellow, orange or brown. The lower surface, which may lack a cortex or bear a prosoplectenchymatous one, is white to whitish grey and often darkens to purple-grey, grey-black, or partly yellow, orange or brown. Rhizines are white to black, simple to densely branched—sometimes long enough to project beyond the lobe margins—and only rarely absent.
The ascomata of Heterodermia are apothecial and . They sit on the thallus surface and are rounded, either or borne on a short stalk. The exposed hymenial surface, or, ranges from pale to dark brown or black; it can be concave or nearly flat and may appear frosted or smooth. A exciple rims the disc—prominent or —and remains distinct throughout the apothecium's life.
In section, the epihymenium is pale brown to brown-black, while the underlying hymenium is colourless. The is usually colourless, only rarely tinged pale yellow. Paraphyses branch toward the top, where their terminal cells broaden and turn brown. The asci are cylindrical to somewhat club-shaped—Lecanora-type—with eight ascospores. Their apex is amyloid and thick-walled, enclosing a clear axial body. The spores develop one or more . They turn grey-brown to dark brown, are ellipsoidal to oblong or fusiform, and have a single septum that often causes a slight constriction. Walls are very thick; internal apical thickenings only appear after the septum forms. A is thin or absent, and the surface remains smooth.
Conidiomata lie immersed in the thallus at first, later becoming emergent. Their cells form short, branched chains and produce conidia enteroblastically. The resulting conidia are bacilliform to short-cylindrical.
The genus Physcia most closely resembles Heterodermia. Unlike Heterodermia, however, it has a differently structured upper cortex consisting of , and its ascospores are different.
Species
Recent estimates have placed the number of species in Heterodermia at about 115. As of July 2025, Species Fungorum accepts 66 species of Heterodermia, but does not yet account for several recent studies that have added many new species.- Heterodermia adunca
- Heterodermia africana
- Heterodermia amphilacinulata – Brazil
- Heterodermia andina
- Heterodermia angustiloba – Asia; Australia
- Heterodermia antillarum – Australia; Central America; Caribbean; Africa; Galapagos Islands
- Heterodermia apicalis – Brazil
- Heterodermia archeri
- Heterodermia arvidssonii
- Heterodermia badia
- Heterodermia barbifera
- Heterodermia borphyllidiata
- Heterodermia caesiosora
- Heterodermia caneziae – Brazil
- Heterodermia comosa
- Heterodermia coralloides – Asia; Australia
- Heterodermia corcovadensis
- Heterodermia delicatula – Brazil
- Heterodermia diademata – Australia; North America; Central America; South America; Africa; Asia
- Heterodermia dissecta – Asia; Australia; Réunion
- Heterodermia dissecticodiademata – Brazil
- Heterodermia dissecticoflabellata – Brazil
- Heterodermia domingensis
- Heterodermia erecta
- Heterodermia erinacea
- Heterodermia exuberans
- Heterodermia flavodactyliza – Brazil
- Heterodermia flavulifera – Brazil
- Heterodermia follmannii
- Heterodermia fragmentata
- Heterodermia galactophylla
- Heterodermia granulifera
- Heterodermia guzmaniana
- Heterodermia himalayana
- Heterodermia hybocarponica – Australia
- Heterodermia isidiophora
- Heterodermia isidiophorella – Australia
- Heterodermia kalbii – Brazil
- Heterodermia koyana
- Heterodermia koyanoides – Australia
- Heterodermia labiata – Brazil
- Heterodermia langdoniana
- Heterodermia linearis – Mexico
- Heterodermia macrosoraliata – Brazil
- Heterodermia minor – Brazil
- Heterodermia mobergiana
- Heterodermia namaquana
- Heterodermia neocomosa
- Heterodermia neocrocea – Brazil
- Heterodermia neoleucomelaena
- Heterodermia nigromarginata – Brazil
- Heterodermia obscurata
- Heterodermia orientalis – China
- Heterodermia papuana
- Heterodermia parva
- Heterodermia phyllalbicans – Brazil
- Heterodermia pindurae – Rwanda
- Heterodermia pinnata
- Heterodermia podocarpa
- Heterodermia pseudospeciosa
- Heterodermia queensberryi
- Heterodermia ramosociliata
- Heterodermia rubrotricha
- Heterodermia sinocomosa – China
- Heterodermia sorediosa
- Heterodermia spathulifera
- Heterodermia speciosa
- Heterodermia spielmannii – Brazil
- Heterodermia subcitrina
- Heterodermia subcomosa
- Heterodermia sublinearis – Brazil
- Heterodermia tabularis – Australia
- Heterodermia tasmanica – Australia
- Heterodermia tremulans
- Heterodermia upretii
- Heterodermia urtasuni
- Heterodermia velata – Brazil
- Heterodermia verdonii
- Heterodermia verrucifera