Pelt Lichens of North America
This is a large, taxonomically-difficult genus of foliose lichens with some 30-40 species native to North America. (33 of which can be found in the Clearwater Valley of south-central British Columbia, the so-called "center of diversity" for the genus, where I was fortunate to have studied the genus under the guidance of Trevor Goward.)
The genus as a whole is readily recognized in the field by its overall soft, leafy appearance, almost always growing on mossy ground, and most importantly, by the rhizines and veins running along the undersurface -- characteristics shared by few other lichens. Solorina, in the same family, can be weakly veined, but it invariably has distinctive apothecia sunken into the upper surface of the thallus. Peltigera, when fertile, bears disc- or saddle-like apothecia on marginal extensions.
I will cover only the 29 species which I have personally seen in the field:
Here is a gallery of representative photos of two dozen of these species.
Key to Species
Here is a rough key to the 29 species I've seen:
Key 1: photobiont green.
Key 2: photobiont blue-green, sorediate or isidiate.
Key 3: photobiont blue-green, at most lobulate, shiny surface (polydactylon and horizontalis groups).
Key 4: photobiont blue-green, at most lobulate, dull surface (canina group).
Here are some additional species to look for:
This species is distinguished from P. leucophlebia by the thick thallus with relatively unwavy margins and almost complete lack of veins. A subtle but useful field character is what Trevor Goward calls its "silver lining": fresh material has a tiny thickened margin that makes a bit of the soft, white underside visible from above. P. leucophlebia tends to look a bit thinner, and has a more irregular outline if any.
P. britannica is very similar, but it tends to be a lower elevation species and you can invariably find at least a few cephalodia growing large and scale-like. P. britannica is also apparently restricted to the west coast. While both P. aphthosa and P. britannica can generate cyanmorphs (see comments and photos under P. britannica), it is much more rare in this species.
I don't know P. chionophylla well enough to comment on it yet.
This is one of the two most common species (the other being
P. leucophlebia). Trevor Goward noted to me that this species tends to prefer
disturbed locations. It is found throughout Canada and extending down into
the Rockies and California, however it appears only P. leucophlebia makes it
down into the southern Appalachians.
This species is very similar to P. aphthosa except for the cephalodia (see
comments there). The cool thing about this species is that it frequently
sprouts cyanomorphs. These look a bit like a parasitic version of P. malacea.
But notice that among the cyanomorph lobes can be found tiny green lobes
where the cyanomorph is reverting to the chloromorph.
This is a very common, widespread, and fast-growing species. Its most
conspicuous feature -- its crisped or frilly margins -- is also the most
variable and least reliable! Always be sure to note the veins and (usually)
abundant rhizines on the underside. Apothecia are not as common in this
species as in others, but when present (be sure to check mature ones!) the
backs of the apothecia should be at most patchily corticate. (In southern
Appalachian material they seem to remain completely decorticate).
This species looks a bit like a cross between P. aphthosa and
P. leucophlebia. As the name suggests (latin for "snow-lover") it prefers
cold places where snow lingers in the spring. I don't have any photos I am
100% sure of, so I won't include any yet.
This species is another confusing one somewhere between P. aphthosa and P. leucophlebia. I usually think "P. leucophlebia" until I see the underside and then just get confused. According to the keys, it sounds most like a P. leucophlebia which has lost its veins. If Trevor Goward hadn't personally confirmed the ID of these photos in the field I wouldn't even trust them myself.
Taxonomically, this belongs with P. apthosa and P. britannica, despite its lack of green algae. It is essentially a green-algal species whose cyanomorph became the dominant form, eventually losing the chloromorph altogether. Note how this species looks much like the cyanomorph of P. apthosa.
It is rather unlike any of the other species, except perhaps the canina group (because of the thick tomentum). However, the complete lack of veins readily distinguishes it from that group. It is very widespread, but especially common in the north.
Note: it can look quite different when growing in dry, exposed locations,
where the dirt and debris can make it difficult to determine that it lacks
veins. In these places it tends to grow smaller, thinner and more irregular,
and the distinctive apple-green coloration is completely lost.
This is the "typical" dog lichen, with its abundantly white-tomentose, dull surface and brushy rhizines. This is a difficult group for me, and I've been warned that even this species itself is likely to undergo major revision in the near future. As such, do not be surprised by a wide range of variation.
The critical points to observe are tomentum (at least on margins if rain has washed much of it off), brush-tipped pale rhizines (often becoming a confluent mass toward the center), and sharply curled-under lobe margins.
P. rufescens and P. didactyla also have brushy rhizines, but both are smaller species, the latter being composed of small rounded, unbranched lobes. P. rufescens prefers much drier, exposed habitats, and has upturned margins. Note that this character is tricky to describe. Both P. canina and P. rufescens have rather conspicuously concave thalli, however the immediate growing margins are abruptly curled under in P. canina, which P. rufescens typically has erect margins.
Members of the P. membranacea subgroup all have distinctive raised veins
and rope-like, pointed rhizines. It's best to check the outer rhizines which
haven't connected with the substrate yet. This is another very useful but
tricky character that is well worth learning.
This most closely resembles a small P. canina. The main problem for me is that it prefers exposed locations where P. canina would presumably also appear smaller and more poorly-developed. The key difference is the margins. See the comments under P. canina.
Some keys group P. ponojensis and P. rufescens since they share similar
habitats, have similar appearance, and both have upturned margins. However,
P. ponojensis has more P. membranacea like veins and rhizines (rope-like) and
more pale underside.
These three species -- P. membranacea, P. praetextata and P. cinnamomea -- form a very difficult complex. All are ambiguously dull and tomentose (check very carefully near the margins with a hand lens). All have narrow, sharply-raised veins and pointed, rope-like rhizines (best to check near the margins).
With practice you can rule out the polydactylon group because even when the faint tomentum has been completely washed away, the surface is still characteristically dull. (The veins are also wrong; P. neopolydactylon and maybe P. neckeri are probably the ones most likely to be confused with these.)
P. canina and P. rufescens have conspicuously brushy-tipped rhizines (again check near the margin). P. ponojensis tends to be smaller and has erect (not down-turned) margins. All three of these are also typically much more thickly tomentose, generally appearing whitish or frosted at a glance. (But not always!)
Within the membranacea complex, the differences are more subtle, and there is significant overlap. P. membranacea is mostly a western species, although found in New England as well; P. cinnamomea strictly northwestern; P. praetextata widespread. P. cinnamomea has distinctive rich cinnamom-brown veins toward the center; it also tends to be more rounded and "nice-looking". The other two have pale to gray-black veins. P. praetextata almost invariably has at least some tiny lobules -- look very carefully with a hand lens at older parts of the thallus, along margins and cracks.
Most keys emphasize a very subtle character involving minute
"erect-tomentose" hairs on the veins and/or rhizines. P. membranacea has hair
on both veins and rhizines; P. praetextata mostly only on the veins;
P. cinnamomea is variable(?); P. degenii doesn't have any such hairs on either
veins or rhizines. Trevor Goward likes to say that P. membranacea has
"soft-looking" rhizines. If this works for you, the more power to
This is apparently restricted to British Columbia and nearby regions. See
comments under the very similar P. membranacea.
This is a very confusing, variable and, alas, relatively common species.
See comments under the very similar P.
P. didactyla and P. extenuata form a distinctive subgroup within the canina group. Both are tiny, almost squamulose things, with round to irregular patches of fine powdery soredia on the surface. They are all likely to be overlooked in the field, and even when noticed, often not immediately recognized as Peltigera species!
P. extenuata used to be a variety of P. didactyla, however once you become
familliar with the two species, it is clear that they are distinct. The
rhizines are completely different, being conspicuously brushy-tipped in
P. extenuata and rope-like (but thin and perhaps fibrillose) in P. didactyla.
P. didactyla remains strictly unbranched and unlobed, and frequently develops
apothecia when mature; P. extenuata is never fertile, and soon elongates into
lobes and later branches. P. didactyla is usually found colonizing disturbed
soil on cut-banks; P. extenuata is mostly on mossy rocks and logs in forests.
See comments under P. didactyla.
This is a very rare lichen known only from a handful of locations in and
around British Columbia. The only one I've seen (the type population in
Clearwater Valley) is growing on a semi-exposed large boulder on the side of
a popular trail. It is most like P. extenuata apparently, but browner,
shinier, less hairy, and darker underneath. Note the difference in habitat,
This is an uncommon but widespread and very distinctive species. It is
the only one I know of that has granular isidia covering the lobe surfaces.
Technically it is in the canina group, but there is no particular reason to
worry about that for identification purposes. The only other species with
laminal isidia is P. lepidophora which is much smaller, and has scale-like
isidia. The granular isidia of P. evansiana are somewhat variable, becoming
slightly flattened or elongate in rare cases where very well-developed, but
never peltate like in P. lepidophora.
This is a tiny almost squamulose species. Once you realize you're looking
at a Peltigera it is immediately identifiable, as there is nothing
else remotely like it. See comments under P. evansiana, the only other
isidiate species I know of in North America.
This is a common and widespread species that's well worth getting to know, as it is used as a reference point for many other less-common species.
It is one of the "shiny" species, a characteristic more easily seen than described. Most of the dull species (the canina group) have conspicuously tomentose upper surface, especially toward the young growing margins. However some (like P. membranacea and P. degenii) can be nearly to completely hairless, but these species will still have a dull appearance. The best way to see this is to look at specimens side-by-side in the field. The difference will be readily apparent at a casual glance. (See also the notes under P. scabrosa.)
Another useful characterist of P. polydactylon is its highly distinctive
constrastive veins. They are well-delineated and quite black toward the
center, constrasting sharply with the small white interspaces. This useful
character is shared by only a few other species, including P. kristinssonii,
_phyllidiosa, and to some extent P. neckeri. Again, this is worth learning,
because it helps put all the other patterns of veination into context.
This is the "other" polydactylon subgroup. It's a tricky species complex which is still in the process of being described, so for now they are all lumped into P. neopolydactla.
It is actually easy to distinguish from the other polydactylon species by
its non-contrastive veins. It is also much broader, and typically has a
gently but conspicuously undulating surface. In my experience it prefers
moister, more shaded habitats, as well.
This species is distinguished by its conspicuously roughened ("scabrose")
surface. I've keyed it out under the canina group, even though it belongs
in the polydactylon group. Despite its dull appearance, on close inspection
you will note that it has no tomentum, and the veins more closely resemble
P. polydactylon than any of the canina group. It is a boreal species.
This species is most easily distinguished by its abundant flat disc-like apothecia, a trait shared only by P. elisabethae (see that species for notes on the differences). It is very shiny and its outermost rhizines tend to be arranged in concentric rows, another trait shared only by P. elisabethae. The concentric rhizines often correspond to concentric dimples visible readily from above (this is less noticeable in P. elisabethae).
It is a common and widespread species, found in moist areas throughout
North America, extending very far south in the mountains.
When lacking apothecia, this species can be difficult to identify. Look carefully for tiny lobules along stress-cracks in older parts of the thallus -- there are always at least a few present.
It is most similar to P. horizontalis, however that species invariably has abundant apothecia, tends to be broader, has better-developed veins, and rarely has lobules. Where the two occur in the same region, they rarely occur side-by-side, one preferring moister habitats than the other (but I forget which!)
This species is readily distinguished by its pitch-black saddle-shaped
apothecia... in principle. Note, however, that young apothecia tend to be a
bit brownish, and one can find remarkably dark apothecia occasionally on
brown-fruited species. However, due to the shiny surface and relatively
small lobes, with care, only P. polydactylon and P. phyllidiosa are likely to
be mistaken for P. neckeri. Note that both P. polydactylon and P. phyllidiosa
should have more highly-contrastive veins, and P. phyllidiosa (a strictly
southeastern species) is invariably abundantly lobulate (check carefully).
This is a distinctive southeastern species. It has a shiny smooth surface
and veins somewhat like P. polydactylon, however it invariably has abundant
lobules along stress-cracks and even margins and apothecia in older parts of
the thallus (look very closely). When apothecia are present, they are
pitch-black just like P. neckeri (and in fact used to be included in that
species), but P. neckeri has less distinct veins and never has abundant
This is one of the few species that regularly grows on the bare trunks of
trees -- nearly all other Peltigera are restricted to at most the
mossy bases of trunks. It is also the only species with powdery soredia all
along the margins. In my experience, the only thing I'm likely to confuse it
with is Nephroma parile(!) However, that species doesn't have
anything even resembling veins underneath.
This is an unusual boreal species that looks quite a bit like it belongs
in the canina group, but the spongy thick veins and stubby rhizines
immediately distinguish it. Apparently it belongs in a taxonomic group all
by itself. It is rare to find it even as far south as southern British
Taxonomically speaking, this species is very different from the rest of
the genus. It is the only one outside the P. apthosa and P. leucophlebia
groups that has green algae. (In this case the cephalodia are borne
underneath the thallus instead of in "freckles" on the surface.) It is very
widespread, but most common up north. Look for it on moist, steep soil trail