Key Characteristics of Hypogymnia

Introduction

Important identification characteristics for Hypogymnia are explained here. More information can be found in Macrolichens of the Pacific Northwest, (McCune & Geiser, 2009).

Scale: Bar=1mm unless noted. Click on images for larger version.
All photos by Bruce McCune unless noted.

Vegetative Structures

Habit

The habit of Hypogymnia species is an extremely useful, but nevertheless somewhat variable, character. In most species the character has a range of variation, but almost always falling far short of the total range seen in the genus. For example, H. occidentalis is almost always appressed, but one often finds a few lobes trailing off the substrate, especially when growing on small branches and twigs. In scattered cases of old thalli on small branches it is fully pendulous, similar to a smallish H. enteromorpha. Most of the typically erect species have deviant forms. For example, H. inactiva is often somewhat drooping and occasionally strongly trailing, misleading observers to think it is H. duplicata. H. tubulosa, while typically erect to suberect is rarely found in an appressed form, although the lobes often arise from the substrate near their ends.

Variations:

erect
erect to suberect
appressed
appressed to suberect
appressed rarely pendulous
appressed to pendulous
pendulous
erect or trailing
erect or appressed

Habit Appressed

H. austerodes

H. wilfiana

Habit Pendulous

H. apinnata

H. duplicata

Diameter

MaxSize (cm): Typical maximum diameter or length of the thallus.
MaxSizeExt (cm): Extreme maximum diameter or length of the thallus (largest observed).

Branching

The branching patterns of Hypogymnia are inherently somewhat variable, depending on crowding and environmental stresses. Nevertheless it is a useful character if one keeps in mind the possibility for exceptions. Some species, such as H. inactiva, H. rugosa, and H. nikkoensis have regularly isotomic dichotomous branching. In other species, such as H. apinnata, the individual branch points are isotomic dichotomous, but sister lobes do not tend to branch at the same length, giving a thallus a less regularly branched appearance than the others previously listed. Many species, such as H. enteromorpha have mostly isotomic dichotomous branching, but frequently make narrower and shorter adventitious lobes. Most of the species with closely contiguous lobes and an appressed thallus, such as H. austerodes, have more irregular branching with numerous unequal dichotomies. In only a few species, such as H. zeylanica, the branching is distinctly pinnate, formed from numerous slender branches at right angles to the main lobes.

Variations:

isotomic dichotomous
anisotomic dichotomous
variable
strongly pinnate

Isotomic Branching

H. imshaugii

H. krogiae

Budding

All species of Hypogymnia produce short bud-like branches, at least on occasion. But in some species these short, adventitious, often swollen branches are useful in diagnosing the species. For example, the presence of numerous bud-like side lobes helps to separate H. enteromorpha and H. occidentalis from H. apinnata. Similarly, H. heterophylla usually produces adventitious lobes (though more slender than in the preceding species), helping to separate it in the field from H. inactiva.

Variations:

absent or rare
occasional
present

H. occidentalis - Budding adventitious branches

H. enteromorpha - Adventitious branches and budding

H. heterophylla - Lobes

Upper Surface Color of Thallus

Like most pale lichens, the thallus becomes increasingly brownish over many years in the herbarium. The yellowish green species (due to usnic acid, as in H. hypotrypa and H. hypotrypella, these found only in Asia) are readily distinguished with fresh material, but the color is equivocal in old specimens. An acetone extract of even an old lobe in a white porcelain spot plate will, however, leave a yellow crystalline deposit of usnic acid.

Most of the characteristically brownish species (such as H. austerodes and H. bitteri) have gray to greenish gray shade forms. Other species (such as H. mollis) maintain a white to light gray color, even in extremely exposed habitats. Most of the species that are typically gray to greenish gray can be almost white to a relatively dark greenish gray, depending on the environment.

Variations:

white to greenish gray
white
gray
gray to greenish gray
greenish gray
greenish gray to brown
brown
white to greenish gray or brown
pale gray to black
white to gray often dark mottled
gray often dark mottled
yellowish green

H. canadensis - Habit

H. rugosa - Lobes

Color When Solarized

In exposed conditions many species become melanized, although some species (such as H. mollis, H. tubulosa) are rarely, if ever, melanized. There appear to be at least two distinct kinds of pigments involved, one producing a browner color (as in H. austerodes, H. inactiva (below)) and one producing a blackening (as in H. imshaugii and H. physodes)

H. inactiva - Upper surface solarized

Dark Mottles

A few species characteristically have dark brown to black mottling on the upper surface, usually in angular patches or lines. In many other species of Hypogymnia dark mottles are occasionally found, but with typical material with little or no mottling.

Variations

none or rare
sometimes present
often present
present

H. beringiana - Habit

H. fistulosa - Upper surface

Black Border

When viewed from above the edge of the black lower surface is sometimes visible. In most species this character is ambiguous because the lobes are only partly or thinly black edged. In a few cases, however, it as a useful character, either by its clear and consistent absence (as in H. mollis) or by a consistent presence (as in H. oceanica). In a few species such as H. duplicata a black edge is seen because the lower surface is greatly expanded (puffy) relative to the upper surface. In other cases the dark pigment simply comes up higher on the sides of the lobes.

Variations:

not visible
sometimes present
often present
present
conspicuous

H. occidentalis - Lobes

H. oceanica - Lobes

Lobe Arrangement

The arrangement of the lobes is usually very helpful in identifying Hypogymnia species at a glance. However, unusual lobe morphologies can be found in most species. As in many other genera of foliose lichens, most species of Hypogymnia can assume a relatively compact form in polluted or otherwise stressful environments. Other variation does not appear to be stress related. One form of Hypogymnia imshaugii from California initially forms a rosette of contiguous lobes, but eventually gives rise to elongate separate lobes arising from near the margins of the rosette. In most species with separate main lobes one can find contiguous portions.

Variations:

contiguous
contiguous to +/- separate
contiguous to imbricate
separate
contiguous or separate
separate to centrally subcontiguous
separate to centrally contiguous
separate rarely contiguous
separate to +/- imbricate

Lobes Separate

H. imshaugii - Habit

H. inactiva - Habit

Lobe Outline (or Profile)

Examine the outline of the internodes when viewed from above. Many species have straight to smoothly and shallowly arcuate sides of the lobes ("even"). In other species (such as H. apinnata and H. enteromorpha) the internodes are "nodulose" with a series of swellings, resembling intestines or the knuckles on arthritic fingers. In many species (such as H. occidentalis and H. oceanica) the lobes are constricted at the nodes and swollen in between ("pinched and swollen"). In a few cases (such as H. austerodes and H. bitteri) the internodes are so short that this character cannot be clearly applied.

Variations:

even
even to +/- nodulose
even to nodulose
nodulose
pinched and swollen
no elongate lobes
even to +/- pinched/swollen

Lobes Pinched And Swollen

H. apinnata - Habit

H. enteromorpha - Habit

Lobe Surface

In all species the upper surface of the lobes begins smooth. As the lobe develops a surface texture often appears. In most species this texture is composed of irregular fine wrinkles (rugose). While many species develop rugose lobes, it is a typical, fairly constant character for some species (e.g. H. occidentalis and H. rugosa). In a few species, such as H. farinacea and H. pseudophysodes, polygonal cracks appear, which typically later develop into flakes of cortex with sorediate edges. Occasionally a warty (verrucose) upper surface is seen, as in the Asian H. papilliformis. Some species that develop black mottles on the upper surface tend to have these as angular blackened depressions (H. fistulosa).

Variations:

smooth
smooth to weakly rugose
occasionally rugose
becoming rugose
polygonal cracked
becoming verrucose
smooth with angular depressions

Upper Surface Rugose

H. canadensis - Habit

H. occidentalis - Upper surface rugose

Lobe Pruina

Pruina are superficial chemical depositis, usually whitish and usually formed from calcium oxalates, causing a frost-covered or floury appearance. Pruina are commonly present on the cortex of the apothecia and stipe, but rarely present in other parts of the thallus. In the Asian species, H. pruinosa, the pruina typically form conspicuous patches or topping on the upper surface of the lobes. In other species, such as H. lugubris (e.g. Crovetto F-111 from Tierra del Fuega, OSC), one occasionally finds inconspicuous pruina on the upper surface, especially near the lobe tips. A few species can have a pruinose disk on the apothecium, such as H. lophyrea (below).

H. lophyrea - Apothecia pruinose

Lobe Width Min-Max (Extreme)

LobeMin: Lobe width (minimum) in mm.
LobeMax: Lobe width (maximum) in mm. This value is a typical maximum size on a given specimen. Lobes are measured at a typical spot along the internodes, not at the often expanded portion at the branch points.
LobeMaxExt: Lobe width (extreme maximum) in mm. The width of abnormally broad lobes is recorded here.

Lobe Width/Height Ratio Min-Max

Min: (unitless) Minimum ratio of width to height of lobes, measured about 1 cm back from the lobe tip, but not at a node. To find this value select one or more lobes that are relatively thick but narrow. Make a transverse section either by cutting with a razor blade or tearing.
W/H Max: (unitless) Minimum ratio of width to height of lobes, measured about 1 cm back from the lobe tip, but not at a node. To find this value select one or more lobes that are relatively broad but thin.

Lobe Tips Perforate

In many species the lobe tips are often perforate, as in H. inactiva, H. occidentalis, and H. vittata. Because lobe tips often become axils as a lobe branches, we view both perforation of the lobe tips and the axils as being the same character. Perforations are typically circular to elliptical and have smooth, non-ragged margins, unlike most holes caused by mechanical tears or herbivory.

The perforations in Hypogymnia mostly follow one of two developmental patterns. In one the perforations are terminal on the lobe tips. When the lobe tip branches dichotomously, the perforation becomes axillary and the new apices elongate. Then the new apices can develop perforations. This pattern leads to many terminal and axillary holes, but only a few holes in the lower surface. In some species, such as H. heterophylla, the perforations are slow to develop, so that lobe tips mainly have pinholes, while large holes are seldom seen until the tip has become an axil. The fraction of lobes developing perforations is quite variable, but typically in the range of 5-75%. Example species with frequent tip perforations include H. apinnata, H. enteromorpha, H. occidentalis, H. sachalinensis, and H. vittata.

In the second developmental pattern the holes form on the lower surface just behind the apices (subterminal) or at the apices. As the lobe elongates, the hole is left on the lower surface. This results in a series of holes laid down on the lower surface, but with few truly terminal or axillary holes. Examples are mostly Asian species, including H. arcuata, H. hengduanensis, and H. yunnanensis. The holes may be so close as to commonly fuse, as in H. arcuata or the extreme case, H. fragillima, where the lower surface is typically more hole than tissue.

Variations:

perforate
often perforate
sometimes perforate
sparsely perforate
rarely perforate
entire

H. heterophylla - Perforate lobe tips

H. occidentalis - Perforate lobe tips

Lower Surface Perforated

In many species the lower surface is perforate. It is strongly so in the Asian species H. fragillima. But in most species perforations on the lower surface are rather sparse and variable. Some species have essentially imperforate lower surfaces, except for perforations from mechanical tears or herbivory. Perforation of the lower surface is often, but not always, correlated with perforation of the lobe tips and axils.

In most species the perforations are simple holes or with an inrolled edge. In a group of Asian species (e.g. H. macrospora), however, the rolled edge of a hole often forms a raised rim around the hole.

Variations:

heavily perforate
perforate
sparsely perforate
sometimes perforate
rarely perforate
entire

H. inactiva - Perforate lobe tips

H. vittata - Lower surface

Cavernulae

Cavernulae are minute but deep pits in the lower cortex, lined with cortical cells, and not penetrating into a hollow lobe.

H. hultenii - Lower surface with cavernulae

H. lophyrea - Lower surface with cavernulae

Thallus Texture

Most species have a texture when dry that is somewhat cartilaginous, tough but yielding. In certain species, however, such as H. rugosa and H. diffractaica, the thallus has a thin, papery feel. This is very useful as a field character in dry weather for identifying even poorly formed H. rugosa, simply by pressing lightly on the thallus with your fingertips. In a few species, such as H. mollis, the texture is relatively soft and flaccid, similar to Evernia species such as E. mesomorpha and E. prunastri.

Variations:

cartilaginous
papery
soft

Medulla

Although most Hypogymnia species always have a very well defined central cavity, in a few species the cavity may be partially or completely filled with loose medullary hyphae. For example, although H. imshaugii is typically distinctly hollow, occasional individuals have solid portions in the lobes, particularly in stressful environments. Other species, such as H. subphysodes, can have both solid and hollow portions on the same thallus. Still others, such as H. mundata and H. pulverata, always have a solid medulla. In these cases the lobes are flatter than the hollow species.

Variations:

solid
mostly solid
partially solid
rarely solid
hollow

H. inactiva - Lobe cavity

H. tubulosa - Lobe cavity

Ceiling

The color of the ceiling of the cavity is a useful character, particularly in western North America. Be sure, however, to check this character well back from the tips. The ceilings of all Hypogymnia are initially white at the extreme tips. In some species the ceiling rapidly darkens away from the tip (e.g. H. inactiva, H. enteromorpha,H. occidentalis), while in others it is usually white (e.g. H. physodes), and in others it is almost always white (H. imshaugii). While the ceiling in H. imshaugii is almost always snow white, areas of local injury or herbivory may darken the cavity. In most of the species with dark ceilings one can find examples where the darkening is reduced to a thin skein of dark hyphae over a light-colored or white background; these should be interpreted as a dark ceiling.

Variations:

dark
dark to grayish
grayish
grayish to white
brownish to white
white
white or dark

Ceiling Dark

H. apinnata - Lobe cavity

H. occidentalis - Lobe cavity

Floor Color

The color of the floor of the cavity is a useful character, particularly in western North America. Be sure, however, to check this character well back from the tips. The floors of many Hypogymnia are initially white at the extreme tips. In some species the floor rapidly darkens away from the tip (e.g. H. inactiva, H. enteromorpha, H. occidentalis) and in others it is almost always white (H. imshaugii). Although this character is somewhat correlated with the color of ceiling, there are numerous species with a dark floor and white ceiling. While the floor in H. imshaugii is almost always snow white, the layer of white hyphae is often so thin that the black lower cortex is easily seen beneath. In this case the floor of the cavity is considered white, not dark.

Variations:

dark
dark to grayish
grayish
grayish to white
white
white or dark

Floor Dark

H. farinacea - Lobe cavity

H. wilfiana - Lobe cavity

Reproductive Structures

Soredia

Soredia are asexual reproductive structures, not covered by a cortex and containing both photobiont and mycobiont.

The presence and form of soredia are very important in differentiating among Hypogymnia species. The most distinctive type are produced in labriform soralia in burst lobe tips, as in H. physodes and H. vittata. In this case the soredia are produced initially on the medullary surface of the lobe cavity. Terminal but externally-produced and often capitate soralia are produced by H. tubulosa. Production of these soralia is often preceded by a darkening of the upper cortex at the lobe tip, sometimes with an oily sheen. In juvenile thalli these incipient soralia can be very helpful in distinguishing H. tubulosa from permanently esorediate species. Other kinds of soralia differ in developmental pattern and final appearance. I have designated 5 types of soralia, apart from those already described.

Type 1 soralia are terminal on short, often upturned, lateral lobes. These are frequent on H. bitteri. These lobes are typically narrower and shorter than the main lobes. The soralia are discrete, often smaller in diameter than the lobe on which they are borne (though occasionally broadening and becoming capitate). These soralia are produced by a gradual dissolution of the cortex, often preceded by a discoloration of the cortex.

Type 2 soralia are also terminal but are produced on the main lobes. They are corresponding larger than type 1 soralia. The soralia are typically less discrete than type 1 soralia and often occur on downturned lobes, like sorediate knuckles on the perimeter of the thallus. These occur in H. bitteri, rarely in H. austerodes, and frequently on the putative hybrids from H. bitteri and H. austerodes from the central and southern Rocky Mountains of North America.

Type 3 soralia are produced along edges of flakes of the upper cortex. These are characteristic of H. farinacea, H. pseudophysodes, and several other species. Frequently these flakes arise from polygonal cracks or rugosity. In the latter case, the cortex breaks along the microridges on the thallus, followed by splaying apart of the broken edges of cortex. The flakes do not penetrate all the way through to the hollow center of the medulla, but do appear to carry at least a thin layer of medullary hyphae.

Type 4 soralia develop by hemispherical semi-corticate warts on the upper surface. They blur the distinction between soredia and isidia, because the cortex appears to be at least partly intact. At fairly high power with a stereoscope, one can see the color of the cortex lightened by a subtle appearance of fine, pale markings. Over time these warts often becoming compound by repeated budding. This form of soralia is most frequently seen in H. austerodes. Occasionally the budding is so pronounced as to suggest true isidia.

Type 5 soralia develop by a gradual deterioration of the upper cortex, simultaneously removing the shiny luster of the upper cortex and becoming minutely roughened. Gradually these rough laminal areas develop soredia, usually in poorly soralia. This form of soralia is frequent in H. austerodes, but also occurs in many other species that produce laminal soredia.

Variations:

none
present
rare
Type 1
Type 2
Type 3
Type 4
Type 5
labriform
terminal capitate
laminal capitate

SorediaPresent

H. bitteri - Lobes

H. physodes - Soredia

Soredia Lip Shaped

H. physodes - Soredia

H. vittata - Apothecia

Soredia Powdery

H. mollis - Soredia

H. tubulosa - Soredia

SorediaTerminal

H. hultenii - Soredia

H. tubulosa - Soredia

Isidia

Isidia are asexual reproductive structures that are minute, finger-like or globular, branched or unbranched, covered with a cortex and containing the photobiont.

True isidia are rare in Hypogymnia. The best examples of true isidia in Hypogymnia are the cylindrical isidia found in the Asian species, H. duplicatoides, H. hengduanensis, and H. zeylanica. The isidiose soredia (type 4) found in H. austerodes approach globose isidia in form and probably in function. Species that typically produce small lobules, such as H. subobscura and H. kosciuskoensis, occasionally produce globose to clavate "isidia". However, given the preponderance of dorsiventral lobules in those species, rather than true isidia, perhaps they are best considered aberrant lobules.

Variations:

none
present
rare
cylindrical
globose
clavate

Isidia Present

H. austerodes - Isidia grading into soredia, note areas with roughened cortex

H. subobscura - Isidia

Lobules

Lobules have a dorsiventral structure as compared to the radially symmetric structure of isidia. They are characteristic in a number of species, including H. subobscura and H. kosciuskoensis. Lobules are differentiated from small lobes by their more frequent presence in small sizes, constricted bases, and laminal or lateral production. Lobules are considered asexual propagules that are readily detached, while small lobes are normally destined to develop and remain attached. Most lobulate species also produce bud-like side lobes, but the reverse is not true: some species produce bud like side lobes but rarely if ever produce lobules.

Variations:

none
rare
often present
present

Lobules

H. krogiae - Lobules

Apothecia

Apothecia are sexual reproductive bodies, usually disk or cup shaped. At maturity, they are lined with an exposed spore-producing surface.

Apothecia Frequency

Frequency of production of apothecia is highly variable in Hypogymnia, but can be fairly constant within species. Some species, such as H. imshaugii, H. inactiva, and H. metaphysodes, more often than not bear apothecia. In a few species apothecia are unknown. Most sorediate species, such as H. physodes and H. tubulosa, produce apothecia only infrequently. A few sorediate species, such as H. pulverata, commonly produce both apothecia and soredia.

Variations:

unknown
rare
occasional
common

Apothecia Present

H. enteromorpha - Habit

H. occidentalis - Habit

Apothecia Habit

The habit of apothecia, in particular whether the apothecia are stalked or not, is frequently mentioned in original descriptions of Hypogymnia species. However, this character and the shape of the receptacle (see below) both need more detailed study of their developmental patterns before we can confidently apply these characters in Hypogymnia.

Variations:

sessile
substipitate
stipitate
sessile to substipitate
substipitate to stipitate

Apothecia Diameter

ApoDiamMax (mm): Diameter of the apothecial disk (maximum) in mm. This value is a typical maximum size based on examining numerous thalli.
ApoDiamExtreme (mm): Diameter of the apothecial disk (extreme maximum) in mm. The width of abnormally broad apothecia is recorded here.

Receptacle

The receptacle of the apothecia ranges from urn shaped to funnel shaped. By receptacle we mean the swollen base of the apothecium, essentially a very short lobe with determinant growth and producing a terminal apothecium, these produced from the upper surface of the main lobes. The character is used frequently by Elix in his works on Hypogymnia in Australasia. Developmental studies are needed, because the receptacle often begins urn shaped and gradually becomes funnel shaped as the disk expands and the receptacle shrinks.

The lower surface of the receptacle (or stipe) often appears scabrous under the dissecting scope. Under the compound scope, the surface is covered with filamentous branched projecting hyphae, the filaments about 8-13 um wide and coated with POL+ crystalline material. The filaments form a mat typically about 50-65 um thick.

Variations:

urn shaped
funnel shaped
urn or funnel shaped
n.a.

Septum in stipe:

In 1901 Bitter published a diagram of an apothecium with a septum in an otherwise hollow stipe below the apothecium (in Parmelia obscurata var. glauca = H. bitteri). I have sectioned many apothecia in Hypogymnia but have seen this characteristic only in H. nitida. The significance and consistency of this character is not clear. Sometimes the base of the apothecium is collapsed, eliminating the cavity, but this is different from the transverse partition drawn by Bitter. In H. antarctica, the stipe is loosely filled with white hyphae, though sometimes this filling is only in the upper portion of the cavity of the stipe.

Variations:

absent
sometimes
present
collapsed base
loosely filled
n.a.

DiskColor

The color of the disk is not very useful as a taxonomic character in Hypogymnia because it is variable in most species, influenced by environment, and rather subjective.

Variations:

brown
brown to reddish brown
brown to dark brown
reddish brown
reddish brown to dark brown
dark brown
tan
yellowish
brown to olive
pale olive to grayish

Spore Min-MaxWidth x Min-MaxLength

SporeLengthMin (µm): Ascospore lengths and widths are measured outside of the asci, in water or 10% KOH, avoiding the runts (aberrant and immature spores). The minimum value is the low end of the typical range in size. Published spore sizes rarely mention the medium in which they were measured. I have found that visibility of spore characters, paraphyses, and hymenium often improve markedly after application of KOH. In Hypogymnia I have not observed a marked change in spore size with application of KOH.
SporeLengthMax (µm): See above; the maximum value is the high end of the typical range in size.
SporeWidthMin (µm): See above.
SporeWidthMax (µm): See above.

Hypothecium

In a thin-section of the apothecium the appearance of the hypothecium (below the spore-bearing layer, the hymenium), differs among species. Terminology for the layering below the hymenium is rather variable among authors, so we define our terms here. All Hypogymnia species have a differentiated subhymenium, a thin layer of horizontal hyphae immediately below the hymenium. This layer is always hyaline, POL- (dark in polarized light), and about 6-14 µm thick.

Immediately below the subhymenium is what we term the hypothecium. The upper part of the hypothecium is a compact tissue that can contain POL+ crystals(bright in polarized light). In other species these crystals are lacking, sparse, or concentrated in the base of the hypothecium. The distribution and abundance of POL+ crystals appears to be a useful species-level character in Hypogymnia. Below the hypothecium is the medullary part of the thalline exciple, which is always somewhat occluded by crystals and POL+ grayish white, and generally somewhat looser than the hypothecium.

Pycnidia

Pycnidia (frequency)

Pycnidia are asexual spore-producing structures of the mycobiont, usually imbedded in the thallus and visible externally as a black dot, occassionally projecting from teh thallus. Anatomically, pycnidia are generally a flask-shaped structure lined with cells that produce pycnospores.

Frequency of production of pycnidia is highly variable in Hypogymnia, but can be fairly constant within species. Production of pycnidia appears to be strongly correlated with production of apothecia.

Variations:

unknown
rare
sparse
occasional
common

Pycnidia Present

H. apinnata - Lobe tips

H. heterophylla - Perforate lobe tips

Schizidia

Schizidia are asexual propagules consisting of flakes of thallus containing the upper cortex and the algal layer.

H. schizidiata - Schizidia propagules

Spermatia Shape

Spermatia are spore-like gametes produced by pycnidia. The spermatia (or conidia, depending on your interpretation) vary only slightly in Hypogymnia. Typically the conidia are almost rod-shaped but slightly swollen toward the ends (bifusiform).

Variations:

rod
rod to weakly bifusiform
weakly bifusiform
bifusiform

Spermatia Min-MaxLength x Min-MaxWidth

SpermatiaLengthMin (µm): Spermatia (conidia) are measured in the same way as the ascospores, though we find them difficult to measure accurately under the microscope. We have therefore switched to measuring them with Photoshop from pictures at 400X. See details in McCune and Wang (2014).
SpermatiaLengthMax (µm): See above.
SpermatiaWidthMin (µm): See above.
SpermatiaWidthMax (µm): See above.

Chemistry

Chemical tests are a well-accepted tool in lichen identification. For details on how to conduct these tests, see Macrolichens of the Pacific Northwest, (McCune & Geiser 2009).

Medullary spot tests

P Test

The P test for the medulla is usually clear. We use a fresh ethanol solution rather than the "stable" version of the reagent. The solution should be a very pale pinkish brown; if it is dark it should not be used. The test should be performed on a fragment of the specimen on a scrap of plain white paper. Species with protocetraric and physodalic acids react quickly to form first a deep yellow, then orange or red color. The color is usually visible on both the thallus (especially cracks in the cortex and torn edges) and by diffusion onto paper when the reagent is applied to a fragment on white paper. In rare cases a yellow reaction occurs when protocetraric and physodalic acids are present in low concentrations. When atranorin is abundant in the cortex, a pale yellow reaction may be seen in the medulla and on a paper background, presumably from diffusion of atranorin in the reagent. Because almost all Hypogymnia contain atranorin, a negative P test is not differentiated from a P+ pale yellow reaction: in both cases atranorin is likely present and protocetraric and physodalic acids are absent.

H. enteromorpha - P+orange-red

H. physodes - P+orange-red

K Test

The white parts of the medulla of Hypogymnia can be K-, K+ brownish, or K+ reddish brown, and rarely K+ deep red purple. None of the normal K+ yellow, orange, or red compounds (such as stictic, norstictic, thamnolic, and salazinic acids) are known to occur in Hypogymnia.

The substance responsible for the K+ reddish brown reaction is 3-hydroxyphysodic acid. The reaction is rather curious and unlike the typical K reactions. This spot test appears to be quite reliable for detecting this substance. The reaction is first apparent wherever there are cracks in the cortex, initially (within about 30 seconds or less) turning the cracks brown, but then the cracks and upper surface gradually reddens (showing through the upper cortex). It takes about 30 minutes for the color to develop fully, but it rarely is necessary to wait more than a couple of minutes to be sure. So the color goes from an initial brown to a distinctly reddish brown.

The K+ red-brown reaction can also be seen on acetone extracts on a white spot plate, where the resulting color can be closer to orange. It can also be demonstrated on undeveloped spots on TLC plates. In the latter case, when the reagent is painted on with a soft brush, the 3-hydroxyphysodic acid spot turns a russet brown.

A weaker, slower, K+ orangish brown reaction is sometimes given by physodalic and protocetraric acids.

In rare instances in Hypogymnia (especially in the H. imshaugii group) one finds the medulla of certain species tinted by yellowish pigments, especially below the apothecia. In at least some cases these are K+ deep red-purple, suggesting the presence of anthraquinones.

H. canadensis - K+ reddish brown reaction

H. physodes - K+ reddish brown reaction

C Test

No C+ compounds medullary compounds have been found so far in North American Hypogymnia species; however, olivetoric acid is known from Asian Hypogymnia.

KC Test

Physodic acid is a very common substance in Hypogymnia that produces a KC+ orange, pinkish, or red color. This reaction is best observed using a piece of scrap of white paper as a background for a fragment including at least several square mm of thallus. The K reagent is applied first, allowing it to thoroughly saturate the fragment. After a minute or two, fresh chlorine bleach is applied, observing the fragment at the moment of contact with the bleach. The reddish reaction from physodic acid usually develops within a few seconds. Fortunately it is more persistent than many C and KC reactions. The reaction can usually be seen through the upper cortex - it is not necessary to attempt to expose white medulla. Although this reaction has a reputation of being unreliable, I have found it to detect physodic acid quite reliably. The most common cause of failure of the KC test is the use of old bleach. `Old` may mean only one day in a clear dropper bottle in a sunny work area. If you are in doubt, keep handy a specimen of Hypogymnia that you know is KC+ red for testing your bleach.

H. inactiva - KC+ red spot test

H. occidentalis - KC+ red spot test

Cortical Spot Tests

The cortical P reaction of almost all Hypogymnia species (those containing atranorin) is negative or pale yellow, depending on the concentration of atranorin. In dark individuals the cortical reaction may be impossible to see.

The cortex of all of the atranorin-containing Hypogymnia is K+Y, although this may be impossible to see on dark specimens. The two usnic-containing species are yellowish to begin with, but do not noticeably react to K.

No C+ cortical reactions have been observed in Hypogymnia.

KC:

The two usnic acid containing Hypogymnia species give a KC+ yellow reaction. In old, browned specimens this may be difficult to see. But an acetone extract of the thallus will be yellowish if usnic acid is present, and the KC reagents applied to the extract will give a yellow reaction. Note also that medullary reactions are often visible through the cortex, giving a false appearance of a cortical reaction. For example, the KC+ red reaction of physodic acid is usually visible through the cortex.

TLC

Each substance listed below is scored as: lacking, trace, accessory, minor, or major, as perceived by thin-layer chromatography(TLC). Other substances occur in Hypogymnia species in North America, but they are less diagnostic. See spot test reactions above.

Atranorin (and chloroatranorin)
Physodic acid
3-hydroxyphysodic acid
2'-O-methylphysodic acid
Physodalic acid
Protocetraric acid (always with physodalic acid)
Hypoprotocetraric acid
Diffractaic acid