Cladonia Grayi

''Cladonia grayi'', commonly known as Gray's cup lichen or Gray's pixie cup, is a species of fruticose lichen in the family Cladoniaceae. It is characterised by small, leaf-like forming its and distinctive upright podetia (5–15 mm tall) that develop into goblet-shaped cups. The species contains several unique lichen substances, primarily grayanic acid, which causes it to glow light blue under ultraviolet light, and has also been found to produce protective pyrrolopyrazine compounds. Its is the green algal species '' Asterochloris glomerata''.

The fungal component shows distinctive growth responses during development that occur only when encountering compatible algal cells, with the fungus growing extremely slowly at ≤1 cm per year in culture. Though found worldwide, ''C. grayi'' is most abundant in Arctic and temperate regions of the Northern Hemisphere. It typically grows on acidic including rotting wood, organic soil layers, and bare ground, showing particular abundance in pine forests across a range of humidity conditions. Two chemical variants (chemotypes) have been documented: one containing only grayanic acid and 4-''O''-demethylgrayanic acid, and another that additionally contains substances of the fumarprotocetraric acid complex.

Taxonomy

The type specimen of ''Cladonia grayi'' was collected in 1928 near Long Creek in Charlotte, Mecklenburg County, North Carolina (originally cited as "North Virginia"). It was distributed as part of Sandstede's ''Cladoniae Exsiccatae'' collection, number 1847. The lectotype specimen is housed at the Farlow Herbarium (FH) at Harvard University and was designated by Teuvo Ahti in 1993 in his work published in ''Regnum Vegetabile''.

Several forms of this species have been proposed, but it is unclear if these historical infrataxa have independent taxonomic significance. As Evans noted about form ''simplex'', "the present form may represent either a stage in the development of one of the more complex forms or a definitely arrested conditions which will not develop further."

:*''C. grayi'' f. ''aberrans''
:*''C. grayi'' f. ''carpophora''
::*A fertile form with abundant large brown apothecia on cup margins or stalks, characterized by dark grayish-green to olive-green podetia lacking squamules.
:*''C. grayi'' f. ''centralis''
:*''C. grayi'' f. ''cyathiformis''
:*''C. grayi'' f. ''fasciculata''
:*''C. grayi'' f. ''grayi''
:*''C. grayi'' f. ''lacerata''
:*''C. grayi'' f. ''peritheta''
:*''C. grayi'' f. ''prolifera''
::*A sterile form with unsquamulose podetia bearing scattered cup-like proliferations.
:*''C. grayi'' f. ''simplex''
::*A sterile form with simple, unsquamulose podetia having entire or nearly entire cup margins.
:*''C. grayi'' f. ''squamulosa''

Common names that have been used for ''Cladonia grayi'' include "Gray's cup lichen" and "Gray's pixie cup".

Description

''Cladonia grayi'' is characterised by two main parts: a consisting of small, persistent leaf-like structures (), and a secondary thallus comprising upright stalks called podetia. The squamules, which form a crusty layer on the , are small (1 mm long and 1–2 mm wide) with wavy edges and tend to grow upward.

The podetia, which are the most distinctive feature of the species, grow 5–15 mm tall and 2–7 mm wide. They are shaped like goblets () with long, narrow stalks expanding into round, globe-like cups at the top. These structures are typically light greyish-green but can appear dark or somewhat brownish. The surface of the podetia is covered with a protective layer () that can be bumpy and may peel off in patches as the lichen ages. The upper portions develop powdery areas (soralia) and measuring 40–130 micrometres in diameter, or they may produce small flaking squamules. The granules are thought to play a play in propagation of the species.

The species' reproductive structures include dark brown spore-producing (apothecia) that appear uncommonly along the cup margins, and more frequent smaller structures called pycnidia that produce a clear fluid.

Ultrastructure

When examined at a microscopic level, the fungal cells of ''C. grayi'' show several distinctive features. They contain nuclei with prominent pores, dense cytoplasmic material, and storage areas for glycogen (a form of sugar). The cells also have specialised compartments called vacuoles that contain granular material, as well as lipid bodies for fat storage. A particularly notable feature is that the fungal cell walls are covered with tiny thread-like projections called fibrils, which extend outward. When fungal cells grow close to each other, these fibrils can interconnect to form meshwork patterns, helping to bind the cells together.

The fungus can also form unique supportive structures called "acellular struts." These struts appear to be modified branches that have lost their internal cellular contents but maintain their outer walls, and they may help provide structural support to the lichen body. These struts are more commonly found in parts of the fungus growing above the surface rather than those in direct contact with the growing surface.

Chemistry

When tested with standard chemical spot tests used in lichen identification, ''C. grayi'' shows distinctive reactions, particularly glowing ice-blue under ultraviolet light. It contains several unique lichen substances, primarily grayanic acid, with varying amounts of congrayanic and demethylgrayanic acids, and occasionally traces of fumarprotocetraric acid complex. Grayanic acid, an orcinol depsidone, is a rare metabolite that has only been reported from ''Neophyllis melacarpa'' and ''C. grayi''.

The thalli of ''C. grayi'' contain a diverse array of carotenoid pigments, including β-carotene, α-carotene, β-cryptoxanthin, zeaxanthin, lutein

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