{{Short description|Genus of lichens}} {{Use dmy dates|date=June 2025}} {{Use Oxford spelling|date=June 2025}} {{bots|deny=Citation bot}} {{Automatic taxobox | image = Krogia macrophylla (10.3897-mycokeys.40.26025) Figure 4.jpg | image_caption = ''Krogia macrophylla'' A & B in the field; C herbarium photograph of holotype. Scale bar=1 mm | taxon = Krogia | authority = Timdal (2002) | type_species = ''Krogia coralloides'' | type_species_authority = Timdal (2002) | subdivision_ranks = Species | subdivision = ''K. antillarum''<br /> ''K. borneensis''<br /> ''K. coralloides''<br /> ''K. isidiata''<br /> ''K. macrophylla''<br /> ''K. microphylla'' }}
'''''Krogia''''' is a genus of corticolous lichens in the family Ramalinaceae.<ref name="CoL_5978"/> It occurs in tropical humid forests and rainforests.<ref name="Kistenich et al. 2018"/> The genus was circumscribed by Norwegian lichenologist Einar Timdal in 2002, with ''Krogia coralloides'' assigned as the type species.<ref name="Timdal 2002"/> These tiny lichens form distinctive coral-like cushions on tree bark, with their scale-like lobes ({{lichengloss|squamules}}) divided into finger-like branches that give them a miniature branching appearance. The genus is quite rare, with only six known species found scattered across mountain forests from the Caribbean to Southeast Asia and the Pacific islands.
==Taxonomy==
The Norwegian lichenologist Einar Timdal circumscribed ''Krogia'' in 2002 on the basis of the Mauritian type species ''Krogia coralloides''; the genus name honours his long-time colleague Hildur Krog. Timdal placed it close to ''Phyllopsora'' but pointed out several decisive anatomical differences: the ascus wall shows only a faint amyloid reaction, the thread-like ascospores are barely 1 micrometre (μm) thick and often coil inside the ascus, the thallus lacks a true medulla yet possesses a distinct lower {{lichengloss|cortex}}, and the chemistry is dominated by boninic acid rather than the depsidones common in ''Phyllopsora''. Because these characters do not fit comfortably into the Bacidiaceae concept then in use, Timdal left the familial placement open,<ref name="Timdal 2002"/> although subsequent workers have treated ''Krogia'' within the Ramalinaceae (''sensu lato'') alongside ''Phyllopsora''.
The genus remained monospecific for several years, but concerted collecting in tropical cloud forests has since uncovered additional taxa. ''Krogia antillarum'' was described from the Greater and Lesser Antilles in 2009, differing from the type in squamule shape and secondary chemistry;<ref name="Timdal 2009"/> ''K. microphylla'' followed in 2011 from a single Dominican cloud-forest site, its epithet referring to its minute lobes. A phylogeny-guided revision in 2018 added three Paleotropical species—''K. borneensis'' (Borneo) plus ''K. isidiata'' and ''K. macrophylla'' (both New Caledonia)—raising the current total to six. All are corticolous inhabitants of humid, montane forests and appear to be rare, each known from only a handful of localities.<ref name="Kistenich et al. 2018"/>
Molecular data place the six ''Krogia'' species in a well-supported clade that is sister to ''Phyllopsora'' ''sensu stricto'' within the Ramalinaceae, confirming that the unique ascus and chemical profile evolved within that family rather than indicating a separate lineage. The genus can therefore be regarded as a diminutive tropical branch of the otherwise mainly epiphytic ''Phyllopsora'' complex.<ref name="Kistenich et al. 2018"/>
==Description==
''Krogia'' forms minute, coral-like cushions composed of numerous overlapping scale-lobes. Each {{lichengloss|squamule}} is at most about 1 mm wide but is divided into forked, finger-like branches barely 0.1 mm across that stand slightly upright and interlock, giving the thallus a finely branched appearance. The surface is grey-green and smooth, yet it is often flecked with tiny crimson patches that instantaneously turn violet-purple when touched with potassium hydroxide solution (the standard K test). No powdery reproductive granules (soredia) or wart-like outgrowths (isidia) are produced. The underside is pale brown to whitish, showing a thin lower "skin" ({{lichengloss|cortex}}), while a distinct {{lichengloss|prothallus}} (margin of fungal strands) is absent.<ref name="Timdal 2002"/>
A thin, gel-like upper cortex—essentially a protective outer layer of tightly cemented fungal threads about 15–30 μm thick—covers the upper surface; unlike many lichens it bears neither crystalline deposits nor traces of embedded algal cells. Just beneath this lies a narrow green {{lichengloss|algal zone}}, roughly 30–50 μm deep, whose {{lichengloss|photobiont}} cells are only about 10 μm in diameter and are sprinkled with microscopic crystals that dissolve in the K test. ''Krogia'' lacks a true medulla (the loose inner fungal layer common in many other lichens), but it does have a second, pale lower cortex up to 30 μm thick where the fungal filaments are longer-celled and loosely bound. Chemical analyses show the thallus to contain boninic acid—an uncommon orcinol meta-depside in this group—together with a closely related compound; under ultraviolet light the thallus therefore fluoresces white.<ref name="Timdal 2002"/>
The lichen reproduces with small, pale brown to medium-brown disc-like apothecia (fruiting bodies) that sit directly on the squamules and seldom exceed 1 mm in diameter. Their margin is inconspicuous and bears minute projecting fibrils at the base. Internally, the hymenium (spore-bearing tissue) is low, only about 40 μm high, and stains weakly with iodine, while the surrounding tissues are densely gelatinised. Each narrowly club-shaped ascus produces eight exceedingly slender, curved ascospores, 22–30 μm long and roughly 1 μm wide, that often coil in a loose spiral and may show one to three faint partition lines. Asexual spores (pycnidia) have not been observed in this genus. These distinctive thread-like spores, coupled with the absence of a medulla and the presence of a lower cortex, separate ''Krogia'' from its superficially similar relative ''Phyllopsora''.<ref name="Timdal 2002"/>
==Species== {{As of|2025|June}}, Species Fungorum (in the Catalogue of Life) accept six species of ''Krogia'':<ref name="CoL_5978"/> *''Krogia antillarum'' {{small|Timdal (2009)}}<ref name="Timdal 2009"/> – West Indies *''Krogia borneensis'' {{small|Kistenich & Timdal (2018)}}<ref name="Kistenich et al. 2018"/> – Borneo *''Krogia coralloides'' {{small|Timdal (2002)}}<ref name="Timdal 2002"/> – Mauritius *''Krogia isidiata'' {{small|Kistenich & Timdal (2018)}}<ref name="Kistenich et al. 2018"/> – New Caledonia *''Krogia macrophylla'' {{small|Kistenich & Timdal (2018)}}<ref name="Kistenich et al. 2018"/> – New Caledonia *''Krogia microphylla'' {{small|Timdal (2011)}}<ref name="Lumbsch et al. 2011"/> – Dominican Republic
==References== {{Reflist|refs=
<ref name="CoL_5978">{{Catalogue of Life |id=5978 |title=''Krogia'' |access-date=16 June 2025}}</ref>
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<ref name="Timdal 2002">{{cite journal |last=Timdal |first=Einar |year=2002 |title=''Krogia coralloides'', a new lichen genus and species from Mauritius |journal=The Lichenologist |volume=34 |issue=4 |pages=293–296 |doi=10.1006/lich.2002.0400}}</ref>
<ref name="Timdal 2009">{{cite journal |last=Timdal |first=Einar |title=''Krogia antillarum'' (Ramalinaceae), a new lichen species from the West Indies |journal=The Bryologist |volume=112 |issue=2 |year=2009 |doi=10.1639/0007-2745-112.2.387 |pages=387–389}}</ref>
}}
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Category:Ramalinaceae Category:Lecanorales genera Category:Lichen genera Category:Taxa described in 2002 Category:Taxa named by Einar Timdal