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@bstarzomski suggested I put together a list of resources that could be useful for others trying to understand bryophytes and lichens in the Pacific Northwest. I’ll try and do it in parts– this one for mosses, later ones for liverworts, hornworts and lichens. Below are online and offline resources I frequently use when trying to find, ID, interpret and relate to mosses. There are upwards of about 1000 species of mosses in the broad region– these resources should help you figure most of them out. I will doubtlessly forget things, so if you have things to add to the guide, pop them in the comments and I will edit them in.

Books and Guides (offline)

• Schofield, W.B. 1992.  Some Common Mosses of British Columbia.  Royal British Columbia Museum. An excellent field guide with keys covering the most common species and genera of mosses in our region focusing on field characters that can be discerned with the eye or a hand lens.
• Vitt, D. H., J.E. Marsh, and R. Bovey. 1988. Mosses, lichens and ferns of northwest North America. Lone Pine Publications, Edmonton, Alta. The only full-colour guide to bryophytes in our region. 
• Pojar, J., and A. MacKinnon. 2016. Plants of the Pacific Northwest Coast. Lone Pine Publications, Edmonton, Alta. What more needs to be said about this book? Covers about 50 bryophytes and a good introduction.

Floras, Guides and Keys (online)

• Elva Lawton’s Moss Flora of the Pacific Northwest (free PDF from Hattori Botanical Laboratory). This is the go to technical resource for identifying mosses in the PNW. You will likely need a microscope to use it to its full potential. Comprehensive, though there have been many taxonomic changes and many new species recorded since its publication in the early 1970s.
• Flora of North America Mosses- Family List for Volume 27 and Volume 28. Comprehensive but harder to sift through as there are many species, genera and families that are not around our region. There is a key to genera (444 couplets!) hosted elsewhere.
• A perspective oriented guide to the bryophyte genera of North America. This is not a traditional dichotomous key and is generally more accessible and intuitive. You will still need to have some comfort with bryophyte language before using it, though it does include a glossary if that helps.
• California Moss eFlora- Excellent resource with keys to every genera in California. Broad overlap, so can be useful to check in on with species descriptions, habitat notes and illustrations.
• Rare Bryophytes of Oregon- a great book highlighting some of the rarer bryos in the region.
• Rare Mosses of Washington- a list of rare mosses in Washington.
• Mosses and Liverworts of the National Forests in Alaska- a quick guide showcasing some of the more common species at the northern end of our region.

Online Collection Databases

• Bryophyte Portal - my first stop when prospecting for or reflecting on moss expeditions. You can search by geographic region, genus, collector, year and more. It has a handy feature where if you select a geographic region and leave the taxon search field empty, you can print out a species list that I use as a primer on what to be on the lookout for. Indexes almost all herbarium collections of bryophytes relevant to the PNW, including collections currently housed on other continents and other coasts.
• Consortium on PNW Herbaria- As above but you can search other groups of “plants”.
• Eflora BC Mosses– Includes many species write ups from Schofield’s _Some Common Mosses of British Columbia_. You can search for mosses by species or genus, all accompanied by distribution maps and many of them are accompanied by a photo gallery
• iNaturalist Bryophytes of the Pacific Northwest project erected by @johndreynolds to catalogue bryophytes in the area. Includes 140,000+ records of roughly 750 species. Can search by Phylum, Class, Order, Family, Genus, Species, user, location, date et al. Chances are if you are seeing something prominent in May in Olympia or Nanaimo, others are also seeing it all around you.

Genus Specific Resources

By my watch, the three most speciose moss groups in the PNW are Sphagnum, Racomitrium and Bryum. All of them can be very challenging, but there is no other way to learn them than to try and figure them out. Lawton does not treat Sphagnum, and her treatments of Racomitrium and Bryum, while great jumping off points, have not kept up with changes within those groups. I have found the following resources particularly helpful:

• Racomitrium: @david1945wagner ‘s Oregon-focused, but broadly applicable treatment of the genus includes a key, visual demonstration of key characters and write ups for 20 species within the genus.
• Bryum/Bryaceae: The Flora of North America Treatment of the family Bryaceae (most of which were traditionally treated as part of the genus Bryum) is very extensive but I found it took some baby steps for me. Luckily, the author of that key (John Spence) also has published a companion set of notes on how to approach the family in North America with an emphasis on asexual reproduction, sexual states, leaf arrangement and leaf morphology
• Sphagnum: to my mind the most nebulous of genera, with about 30 species in the region. While there are no region-specific guides, many of the species are cosmopolitan, so you can use some of these resources together with the Flora of North America treatment of the genus to get to species (or at least subgenus).

• Books: I use Sphagnum Mosses: Stars of the European Mires an incredible visual guide with broad overlap of species in our region. Sphagnum Mosses of Eastern Canada is similar and has an extensive visual key to subgenera and species, but the production quality is not as high. Still a great resource.
• Dr. Dale Vitt has spent decades looking at Sphagnum in Western North America. He put together two great guides– This one specific to Alberta peatlands (again with broad overlap) and this review and key to all bryophytes common in N. Am. peatlands, with a heavy emphasis on Sphagnum.
• iNaturalist user @janetwright has put together Sphagnum with Slides a compendium of species observations with microscopic photos to show the key anatomical and morphological features that are not necessarily visible in the field.
• The Geological Survey of Canada published the Macroscopic Identification Key to 36 Species of Sphagnum in Eastern Canada, which is a great field guide for characters visible with the naked eye (or at most a hand lens). The majority of the species in this guide occur in our region as well.

Microscope equipment and tips

I wrote another post detailing resources for microscopy. I would like to follow it up with some basics for how to use the microscope to look at cross sections, see cell walls, papillae and cell types. For now, the resources listed in this post will get you mostly there.

@bstarzomski suggested I put together a list of resources that could be useful for others trying to understand bryophytes and lichens in the Pacific Northwest. This entry will be about liverworts. There are around 250 species in our region and many of them are cosmopolitan. This is convenient because literature on liverworts is more scant than that devoted to mosses. Below are paper, online and database resources that will be helpful if you haven't stumbled across them yet. Please comment on any that I am forgetting and I will be edit them in to this document.

Books and Theses

My go to resources for liverworts are typically of the printed variety, though some are also available online. The best starting point is Wilf Schofield's Field Guide to Liverwort Genera of Pacific North America. It includes keys, descriptions, habitat and distribution notes. It is lavishly illustrated with great line (and dot) drawings of every genus in the region. Like Schofield's Common Mosses of BC book, it has a helpful section for each genus about what else it could be mistaken for and how it can be distinguished from those other taxa.

The most obscure but most regionally relevant of these is Judith Godfrey's 1977 Thesis on the Liverworts of Southwestern BC. It has a comprehensive key to genera and within those subsequent keys to species. It is available at the UBC library but thankfully more accessible online as a PDF. On this same beat @gwark mentioned a similar thesis of the same antiquity-- Bryogeography of South-Eastern Alaska by Ian Worley. It has helpful species descriptions that, given the lush liverwort (and moss) flora of the region probably covers many if not all of the species found within 50km of the coast. @gwark has repurposed the original Worley descriptions for the web and updated the taxonomy, so you can find much of that work here as well.

There are quite a few authoratative treatments of liverworts, but they are generally out of print and hard to track down. Volumes 1-3 (of 6) of Rudolf Schuster's Hepaticae and Anthocerotae of North America are now available online. You will need to log in and borrow them, but they are as comprehensive as it gets, albeit less so for the west as the volumes focus on liverworts east of the 100th meridian.

I would be remiss without mentioning my favourite liverwort book- Jean Patton's The Liverwort Flora of the British Isles, which is comprehensive, contemplative, gratuitously illustrated and broadly applicable to most of the species and genera in our region.

Online Resources

Bryophyte Flora of North America Preliminary Treatments of Liverworts (by family and genus) is getting closer and closer to completion. This reflects the more recent changes in taxonomy and species distributions.

David Wagner's Guide to the Liverworts of Oregon is an html based system for keying out liverworts. Entries are accompanied by great photographs and contemplations of the many species in our region. You will need to purchase access to this and have files sent through the mail.

Online Collection Databases

• Bryophyte Portal - my first stop when prospecting for or reflecting on all bryophyte expeditions. You can search by geographic region, genus, collector, year and more. It has a handy feature where if you select a geographic region and leave the taxon search field empty, you can print out a species list that I use as a primer on what to be on the lookout for. Indexes almost all herbarium collections of liverworts relevant to the PNW, including collections currently housed on other continents and other coasts.
• Consortium on PNW Herbaria- As above but you can search other groups of “plants”.
• Eflora BC Liverworts– Focuses on the hepatics of British Columbia_. You can search for liverworts by species or genus, all accompanied by distribution maps and many of them are accompanied by a photo gallery
• iNaturalist Bryophytes of the Pacific Northwest project erected by @johndreynolds to catalogue bryophytes in the area. Includes 140,000+ records of roughly 750 species. Can search by Phylum, Class, Order, Family, Genus, Species, user, location, date et al. Chances are if you are seeing something prominent in May in Olympia or Nanaimo, others are also seeing it all around you.

Maybe it is the lingering effects of this Beavis and Butthead clip, but the idea fungi growing on lichens seems inherently alluring. There are some really capable specialists in lichens and lichenicolous fungi on iNaturalist. I am not one of them. In my attempts to improve, some resources have been very helpful.

• Mike Haldeman and Sunia Yang's Lichenicolous Fungi of the Pacific Northwest Database is indespensible, as you can search my host lichen genus or species as well as by parasite genus. Records come up with brief descriptions of the taxa as well as literature.
• Particularly helpful on that site is the listing of publications with keys to lichenicolous fungi by genus. January can be a bit of the doldrums for those who like to get out, but read a paper about all the fungi growing on Cladonia and suddenly a world of hunting and cryptic diversity is opened up.
• The British Lichen Society has a great introductory page with resources on lichenicolous fungi with a particularly enticing visual guide to fungi known from Xanthoria parietina. Granted, these things are half-a-world away, but so little is known about the distribution and diversity of these organisms. Xanthoria parietina is considered a "weed" in our area-- you will find it all over concrete and some trees in coastal areas. Is this weed hosting fungi unique to our region or are its pathogens stalking it around the globe? This thesis by Antonia Fleischhacker linked in the comments below also looks at the X. parietina fungal bouquet.
• iNaturalist has a great Lichenicolous Fungi of the World project that has more than 250 species as well as avid observers and identifiers. User @lumenal has also set up another project, Lichenicolous Fungi, in which you can post your observations even if you can't ID it to species. Just add your observation to this project when uploading.
• For checking collections, the Mycoportal is a central repository of global records for fungi that you can use in tandem with the Lichen Portal to look at the distribution, diversity and taxonomy of these organisms by geographical region. Lichenicolous species are searchable in both systems.

Perhaps more experienced and literate lichenicolous people @eullstrom @ahuereca @toby_spribille can chime in with more print and online resources for lichenicolous fungi in the PNW.

There are about 5 species of hornworts in British Columbia, with their numbers increasing as you head sound. Hornworts are ephemeral things that seem to only be prominent (or as prominent as a 1cm plant can be) in the spring when their large horns/sporophytes are developing.

Where and when to look for Hornworts
In coastal British Columbia, hornworts seem to show up in February and March and loiter until early summer around seeps over thin, finer soil and rock. There are also records all over the west for agricultural fields-- presumably soils of the moisture retentive "clod" type.

What you need to identify Hornworts
Ideally you will have fertile material with mature spores. You will know you are at the right stage when the long sporophyte begins to dehisce and reveal the spore mass within. Barring that, you can look for little bulbils (asexual propagules) on the underside of the thallus. The shape of the thallus and the abundance and form of the protuberances can also be helpful. The three genera of this region can be distinguished based on the presence of the bulbils (Phymatoceros bulbiculosus) and, in the species lacking those bulbils, the colour of the spore mass: yellow in Phaeoceros and black in Anthoceros.

Hornwort ID resources

• @david1945wagner 's Hornworts of Oregon guide includes visual key to all species that are likely to be found between BC and Oregon. There is particular emphasis on spore ornamentation, which is crucial for ID to species in some cases. The site is also rich with complete and visual species descriptions, contemplations and relevant literature. This is my first stop.
• Doyle and Stotler's 2006 Treatment of the Liverworts and Hornworts of California
• Hornwort taxonomy seems particularly plagued by ephemeral names and synonymy. This Stotler and Crandall-Stotler 2005 paper is a good place to try and relate one name to another. It also gives a summary of all species recorded in North America as well as their distributions
• General hornwort biology, morphology, anatomy and classification is well covered and abundantly referenced in this 2020 review paper by Frangedakis et al. (open access).

Hornwort Databases

Like mosses and liverworts, hornwort collection records and distribution maps can be excavated from the Bryophyte Portal.
• Likewise, a search through the Hornwort section of the Bryophytes of the Pacific Northwest iNaturalist project erected by @johndreynolds will give you a sense of what to look for, where to look and when to look.

A final comment about collecting
There are only about 50 records of hornworts in herbarium collections for the province of British Columbia. Their diversity, distribution, ecology, phenology et al. are not well understood in our region, so any records for this group are worth collecting provided the population is vigorous and you have permission/permits to collect where applicable. Below you can see @jstraka 's recitation of a helpful rule: "The rule of thumb I have heard for collecting (at least for plants) is the "1 in 20" rule - The further comments below by @david1945wagner clarify the rule "It is a rule of thumb that you should find at least 20 individuals before collecting just 1. There should be 40 present to collect 2. It's a rule of thumb, meaning to be applied on a case by case basis. If applied strictly, it might result in populations of a rare species reduced to 19. With lichens or bryophyte colonies it may mean to take only 5% of the patch or thallus." The full write up of the rule can be found down the page here in a 1991 issue of the Plant Science Bulletin from the Botanical Society of America.

You should collect and send hornworts that meet these criteria to your regional herbarium. If you have questions about this, feel free to contact me. Instructions for submitting material to the UBC Bryophyte Herbarium, for example, can be found here.

Almost at the end of this series-- what better way to finish than with the most complex and diverse group in the bunch. Lichens have long been the enigmas of photosynthetic life. Treated in turns as plants and algae and fungi, they are now classified based on their fungal component, but widely treated as diverse commensal-to-symbiotic communities consisting of fungal partner(s) (typically an ascomycete but sometimes a basidiomycete) and "photobiont(s)", a photosynthetic algae and/or bacterial living within or about those fungal tissues. Recent work has shown that there can be a lot more going on, with basidiomycetous yeasts occuring within ascomycetous thalli alongside non-photosynthetic bacteria. The following resources I have found useful in making sense of all of this while looking at lichens in the Pacific Northwest.

Books (offline and occasionally online)

• McCune and Goward's Macrolichens of British Columbia V.1: Foliose Species
  https://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/Srs08.pdf
  This is a lavishly illustrated technical key to the foliose lichens of BC. Great resource. Available in print or free as a PDF from Government of BC.

• Goward's Macrolichens of British Columbia V.2: Fruticose & Squamulose Species
  https://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/Srs09.pdf
  This is a lavishly illustrated technical key to the fruticose and squamulose lichens of BC. Great resource. Available in print or free as a PDF from Government of BC.

• @mccuneb and Geisler's Macrolichens of the Pacific Northwest
  https://osupress.oregonstate.edu/book/macrolichens-of-pacific-northwest
  The best field guide for macrolichens of our region-- portable, comprehensive with keys to groups, genera and 500+species, half of which get the lavish full-page treatment. It also includes an incredibly helpful (and illustrated) glossary as well as introductory notes on techniques and applications.

• Stephen Sharnoff's Lichens of California (field guide)
  https://yalebooks.yale.edu/book/9780300195002/field-guide-california-lichens/
  Incredible photography from one of the collaborator's on Brodo's _Lichens of North America_ project. Lots of overlap with out region, but not as on point as the McCune and Giesler book.

• Microlichens of The Pacific Northwest (2 volumes)
  https://www.wildblueberrymedia.net/store/microlichens-of-the-pacific-northwest-volumes-1-and-2
  This is a beast of a resource-- a technical key with 1000+ species of tiny little crustose lichens that many people might mistake for paint or guano. Volume 1 is a visual key to groups and genera, while volume two includes keys to species within alphabetically arranged genera. Great glossary here as well.

• Field Key to Coastal and Seashore Lichens by Frank Dobson
  https://www.nhbs.com/a-field-key-to-coastal-and-seashore-lichens-book
  This is a publication focused on maritime lichens of the British Isles, but many of them are cosmopolitan. The coastal habitat is very accessible in our region, but surprisingly underexplored. This. is a good starting point.

• Biotic Soil Lichens of the Columbia Basin by Bruce McCune and Roger Rosentreter
  https://northwest-lichenologists.wildapricot.org/page-1854217
  For dryland regions on the PNW, these soil lichens create pretty amazing little communities in pretty harsh environments.

• Urban Lichens by Jessica Allen and James Lendemer
  https://yalebooks.yale.edu/book/9780300252996/urban-lichens/
  This one focuses on the urban habitats of the US NE. While not entirely homologous to urban environments in our region, it makes for a good jumping off point for lichen enthusiasts who spend most of their time in cities.

• The Secret World of Lichens: a young naturalist's guide by @troymcmullin
  https://www.fireflybooks.com/catalogue/product/14172-the-secret-world-of-lichens-a-young-naturalist-s-guide
  Aimed at younger readers drawn to the mystery and majesty of lichens, this is a book I would have killed for as a kid. Very visual, it presents some common lichens in the context of their intriguing forms and qualities.

Online Resources

• Common Macrolichens of the Pacific Northwest
  https://lichens.twinferntech.net/pnw/index.shtml
  A spectacular and visual online guide to the major macrolichens in the PNW by Bruce McCune and Sunia Yang. Includes a multi-entry search for species by numerous macroscopic features.

• Ways of Enlichenment
  https://www.waysofenlichenment.net/
  The product of numerous lichenologists but brought together by Trevor Goward's vision of a lichen guide for the region, this is a gallery of hundreds of micro and macrolichen species in the region organized by growth form, informal group, formal groups, genera and species. 11,000 photos. It also includes a link to Bruce Ryan's Working Keys for Lichens of North America, which is a bottomless resource if you want to really dig into different genera (in different habitats).

• Willa Noble's Thesis on Lichens of the Coastal Douglas Fir Zone
  https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/831/items/1.0095921
  Comprehensive treatment of all lichens in the Coastal Douglas Fir Zone that dominates the southern coast of BC and the northern coasts of Washington State. A great (free!) reference with keys to genera and species. Taxomony is somewhat dated, but that can be addressed with a simple search after you have tried to figure something out.

• Lichen Portal
  https://lichenportal.org/cnalh/collections/map/index.php
  The central repository to look at the distribution, diversity and taxonomy of lichens. Map based searches are helpful to make checklists and compare your collections with those made previously in your region of interest. You can search by family, genus, species, collector et al.

• Maritime Lichens Website
  http://www.lichensmaritimes.org/index.php?task=introduction&lang=en
  This website is based in Europe but really digs into the nuts and bolts of lichen zonation in maritime regions, complete with abundant photos for hundreds or maritime-to-maritime-adjacent species.

• A webtool for measuring Cortex, Medulla and Axis ratios for Usnea
  https://welliam.github.io/measure-cma/
  This tool was developed by iNaturalist user @wweellll as a simple way to calculate the ratio/proportions of cortex, medulla and central axis in relationship to overall diameter in Usnea.

Lichen equipment

• The NW Lichenologists website has a bunch of information about sourcing materials for studying lichens.
• The only thing I will add is that lichens are made somehow more colourful by the use of UV light and chemicals. I use a 40$ 10W, 365nm UV flashlight that makes lichens (and liverworts) come alive with diagnostic colours.
• You can use household bleach for "C" solution when you encounter it in keys. K and Pd are harder to come by. You can order KOH crystals online and mix them 10g to 100ml of water, but Pd is very hard to come by.
• When collecting crustose lichens, a long blade (knife, multitool, razor) will help for epiphytes.
• For crustose species on rock, you are likely going to need a big hammer and a big chisel and may the kitty gods help you if the rock is smooth and round.

Like the other entries in this series, if you have more that you think should be added, comment below and I will try and add it in a future edit.

Field and lab identification of Sphagnum is extremely challenging. I say this after three years of trying to get a handle on the ~30 species of the genus found in my region. Not only do you have to look at a number of features and do a number of preps, but often the character overlaps between species are such that you can be left hanging on an unresolved ID. In the WORST CASE SCENARIO when IDing Sphagnum, you might need to do the following steps:

Field Characters (Video One)
(1) Interpret the overall habit and growth form (Does it form loose, low-lying carpets, solitary sprigs, diminutive cushions, bulging hummocks?)
(2) Interpret colour-- while highly variable depending on exposure and hydration, among other things, some Sphagna are reliably red or brown or orange. Some are shiny when dry. Some plants are candy-striped.
(3) Consider the habitat (is it a forest species? Is it below the water line for most of the year? Is it along drainage margins? Is the habitat associated with calcaerous rocks of basic run off?)
(4) Determine the shape of the capitulum (Stellate? Flat? Hemispherical?)
(5) Search for the presence of and determine the prominence of an apical bud at the center of the capitulum.
(6) Are the leaves on the branches of the capitulum arranges in five tidy ranks around the branches?Do they come off at 90 degrees to the branch? Do they curve backwards as they dry?
(7) Are the branch leaves acute or obtuse, hooded ("cucculate") or fringed?
(8) Look at the plant side on to look for the pattern of emerging branches, both in bud form and in mature form further down the stem. How many branches are presence in each cluster and of those how many are growing outward ("divergent") and how many are hanging down ("pendant").
(9) What is the shape and orientation of the stem leaves? These are the leaves that come directly off the main stem. They are best seen by plucking off the capitulum and if neccessary the first few fascicles (clusters) of branches as you go down the stem. Are they triangular? Tongue-shaped?Appressed to the stem? Hanging down? Tattered?
(10) What is the colour of the stem? Red? Green? Brown? Pale? Variegated?
(11) Are sporophytes present? Some species carry them more reliably than others.

Microscopic Characters
To prepare sampled for the microscope I do the following steps.
(1) If specimen is fresh and wet, proceed to step 2, otherwise hydrate dried specimen by running it under tap water and rhythmically squeezing and releasing about 10-20 times while water runs. Slow route it to just let it sit in small tub of water for 30 minutes.
(2) Pluck off the capitulum, stain it, rinse it and press it under a slide to make branch and branch leaf cross-sections. Mount those to a slide in a drop of water, cover them with a coverslip. (Video 2)
(3) Pluck branch leaves from excess stained capitulum using tweezers and mount them to a slide. Some should be facing concave side up and some should be facing concave side down. (Video 3)
(4) Pull off fascicles to expose the stem and stem leaves. Stain a 1" fragment, rinse it. Pluck stem leaves with tweezers and put them on a slide in a drop of water with a cover slip overtop. (Video 4)
(5) Take remaining stem material and make 1 tangential section and 1 cross section. Put them on a slide in a drop of water with a cover slip overtop. (Video 5)
(6) delicately try to denute one of the stained branched of its leaves. Put it on a slide in a drop of water with a cover slip overtop. (impossible to make video of)

This takes about 2 minutes altogether and will leave you with the following:

• Branch Leaf Cross Section (Slide 1, Coverlip 1)
• Branch leaf whole mount upper surface (Slide 1, Coverlip 2)
• Branch leaf whole mount lower surface (Slide 1, Coverlip 2)
• Stem Leaf whole mount (Slide 2, Coverlip 1)
• Stem cross section (Slide 2, Coverlip 2)
• Stem tangential section (for surface cells, pores, fibrils) (Slide 2, Coverlip 2)
• Branch axis whole mount (for surface cells, pores, fibrils) (if you can keep track, Slide 1, Coverslip 2)

When all this is done, you will have everything you need to hopefully identify your Sphagnum using the Flora of North America Sphagnum key.

Syntrichia is one of the easiest moss genera to recognize. The broad leaves in a pinwheel arrangement, often with a red-orange hue around older growth, in combination with the prominent "awn" (a clear, discrete hairpoint at the end of the leaf) make it unmistakeable. If you are marginally lucky, the erect sporophytes with the elongate and twisted teeth are another feature that help define this group. After that, however, it gets a little hazy. Of the roughly 1000 iNaturalist observations of the genus in my immediate region (coastal SW BC & WA), about 60% of them purport to be Syntrichia ruralis, with S. princeps being the second-most observed species in the genus. These two are harder to distinguish that I thought. The problem is compounded by other very similar-looking taxa, like S. ruraliformis, S. papillosa and S. norvegica. This post attempts to seperate the species of Syntrichia based on hand-lens level features and habitat. Each linked species hereafter takes you to an iNaturalist observation that I think is representative. At the end of this post is a link to Syntrichia ID resources.

Syntrichia ruralis:

Habitat: This common species can be found epiphytic on hardwoods, concrete, mortar, limestone and limey soils from sea level to above the tree line. According to herbarium records, it is predominant species of arid regions.
Distinguishing characters: When wet, the leaves are squarrose-recurved, meaning they arch back to a 90 degree angle with the stem. The leaf margin is rolled over at the edges almost all the way to the apex of the leaf.
Advanced Characters: This species, unlike similair-looking S. princeps, has antheridia and archegonia on seperate plants ("dioicous"). To see this you can peel back the leaves around a developing sporophyte, place the base of the sporophyte in water on a slide and then squash it with a cover slip. Under the microscope, it will look like this if it only has archegonia, whereas it will look like this if it has both archegonia and antheridia.
One Line ID: leaves bent back to 90 degrees, margins rolled almost to the tip.
addendum: @terrymcintosh has chimed in below with his considerable experience and mentions that three other species are now verified as occuring in the coastal regions. All three of them are part of the Syntrichia ruralis complex treated in this A Scandinavian study and as best I can tell, a microscope would be needed to tease them apart. Syntrichia virescens is much like ruralis, but the leaf margins are plane in the distal half and under the microscope, the upper surface of the costa in cross section is covered by 1-2 rows of "stereid" cells (small, thick walled, tiny lumen), whereas in S. ruralis this is 3-6 rows thick. The other two species can be distinguished based on mamillae and papillae. Syntrichia papillosissma has tall bulging mamillae crowned by 1-2 papillae, whereas Syntrichia subpapapillosima, is TBD

Syntrichia princeps

Habitat: Concrete walls, mortar, cliffs crevices, sandy areas with mineral soil. Typically low elevation. Likes urban areas.
Distinguishing characters: These plants produce lots of sporophytes (reproduction is easier when every plant has the right parts). Schofield's guide notes that from the side, annual growth increments are visible as clusters of leaves along the stem. Unlike S. ruralis, S. princeps is supposed to have leaves that are constricted near mid-leaf. Even still I find this is a hard one to be sure of without a microscope.
Advanced Characters: A cross section through the leaf of S. princeps should show hyroids in the costa which is absent in S. ruralis and S. norvegica. Hydroids are wide-lumened water-conducting cells that are dead at maturity. I find these hard to recognize but you can look here for a iNaturalist discussion about it with links to good examples.
This species, unlike similair-looking S. ruralis, has antheridia and archegonia on the same plant in the same regions ("synoicous"). To see this you can peel back the leaves around a developing sporophyte, place the base of the sporophyte in water on a slide and then squash it with a cover slip. Under the microscope, it will look like this, with round antheridia mixed with occasional long-necked bottle-like archegonia. In S. ruralis, you will only find archegonia in these regions.
One Line ID: SYNOICOUS DISTURBOPHILE WITH CONSTRICTED MIDLEAF

Syntrichia norvegica

Habitat: Subalpine to Alpine on mineral soil and rocks.
Distinguishing characters: almost identical to S.ruralis, but with a red awn. Sometimes said awn can be green, in which case you'll need a microscope and some razors to distinguish it from S. ruralis. The leaves are purported to be "recurved" (rolled over at the edges) along most of the margin expect the distal 1/4 of the leaf, where the margin is plane/flat.
One line ID: RED AWN AT HIGH ELEVATION

Sytrichia laevipila

Habitat (in this region): Garry Oak Bark
Distinguishing characters: This is a tiny little Syntrichia with plane margins. It can be confused with small forms of S. princeps, but the margins on the latter are rolled back.
One line ID-TINY ON OAK WITH PLANE MARGINS

Syntrichia papillosa

Habitat: Epiphytic -- found once on a street tree in Vancouver
Distinguishing characters: This is going to look like standard Syntrichia except the margins are incurved (not rolled back or plane) and gemmae are purported to be present.
One Line ID: EPIPHYTIC WITH INCURVED MARGINS

Syntrichia latifolia

Habitat: Epiphytic on tree trunks (especially street trees in urban areas)
Distinguishing characters: The lack of a hairpoint, rounded leaf tips and medium size distinguish it from other species in the province. Some forms of S. laevipila lack the hair point, but these are much smaller. Under the microscope, S. latifolia a
One Line ID: MEDIUM-SIZED ROUND LEAVES NO HAIRPOINT ON TREES

Syntrichia ruraliformis

This species is not recognized in the Flora of North America treatment of Syntrichia, and all collections are synonymized with Syntrichia ruralis. In Europe, this taxon if variably recognized as a species, subspecies and variety. I mention it only because @michael-lueth pointed out an observation of similair form here on the eastern Vancouver Island
Habitat: Sand dunes, stony and rocky flats.
Distinguishing characters: Gradually tapering leaves that come to a point and end in the awn. The tips of the leafy section of the leaf tend to be clear (non-photosynthetic).
One Line ID: ACUMINATE SAND FORM WITH IMPOSTER SYNDROME AND HYALINE LEAF APICES

Links to Syntrichia Treatments

Flora of North America Treatment
California Moss eFlora Treatment
A Scandinavian study taking a multi-pronged but granular approach to teasing apart the very similar species of Syntrichia. Includes revised key and phylogeny but based on Scandinavian material.

Scapania is like the Sphagnum or liverworts--instantly recognizable to genus but then agonizing to go beyond that point. The unequally bilobed leaves with their ovate-reniform lobes are an instantly recognizable feature. There are about a dozen species in coastal BC, many clustered in subalpine habitats. I will try to add more to this table as I am able to dig up records. Using a combination of habitat and leaf features, it is possible to get to species. It turns out the shape, relative size and attachment of the characteristically unequal leaf lobes is the key to figuring this genus out. Three words from this table should be off-putting so I will explain them up front: Dorsal lobe refers to the overlapping part of the lateral leaf that you see on top when you look down at Scapania from above. It is generally smaller than the underlying ventral lobe, which is most visible and prominent when looking at the underside of the shoots. Ventral leaf decurrency refers to the way the leaf is attached to the underside of the lobe. Instead of attaching transversely across the stem, a decurrent leaf runs down along the edge of the stem for a while. This great photo by Richard Droker shows the ventral side (on the left) next to the dorsal side (on the right) of Scapania bolanderi. You can see that the leaf margin begins to parallel and descend along the stem. It is "decurrent".

Each species below is linked to an iNaturalist observation that attempts to demonstrate the features in this table. If you want to get very deep in to Scapania, try the provisional Bryophyte Flora of North America Key to Scapania (link to pdf treatment of all species of family Scapaniaceae in North America north of Mexico).

Frullania is an utterly fascinating liverwort genus. Suffused with little pockets and alcoves in and among its leaves, this leafy hepatic is a remarkably rich respository of cryptic biodiversity. In the US southeast and British Isles, studies have shown the genus to host handfuls of fungal species. Meanwhile, in Atlantic Canada, Frullania asagrayensis has been described as a "cyanobacterial garden" that hosts a stable supply of photobionts held at the ready for lichen symbioses. I have noticed lots of little green algae and cyanobacterial in the pockets of Frullania, but have not seen any published work that looks at the variety of life hosted in our6 regional species. 

Similar Genera

Frullania, while generally smaller, can easily be mistaken for other epiphytic and epilithic liverworts with tightly overlapping leaves. I have at times confused it with both Porella and Radula, The key it to look closely at the undersides of the plant. In Porella, the underleaf is large and unlobed, while the lateral leaf has a large lobe on the upper surface ("dorsal lobe") and a much smaller but leaf-like lobe on the underside of the stem ("ventral lobule"). In contrast, Frullania has a bilobed underleaf and the lateral leaf, while divided into a dorsal lobe and a much smaller ventral lobule, has distinctive helmut-shaped lobules on the underside of the stem, often accompanied by a little projection of leaf tissue called a "stylus".  Like Frullania, Radula has a closely overlapping set of dorsal lobes on the top of the stem, the lobes on the underside are formed by a fold at the bottom of the lateral leaf and the underleaf is entirely absent. So-- if you see a liverwort with tightly overlapping leaf lobes on the top surface and you are not sure, just flip it over and look for the underleaf-- if it is present and bilobed, it is Frullania. If you cannot see the underleaf in all that mess, look for the round little hemlets, also a giveaway for the genus. 

Distinguishing species of Frullania

Regional species of Frullania are distinguished based on the shape of the dorsal lobe, the presence of special cell types called "ocelli" (eyes, if you will-- they show up as darker cells in the leaves, often forming lines) and the shape of the underleaves and lobules. To get in to the weeds, you can check the provisional treatment of Frullania in the Bryophyte Flora of North America. The table below distinguishes the 6 taxa of coastal BC based on these features as well as their size and habitat.  

Table of Frullania species in the Pacific Northwest

One Line IDS

This is the @johndreynolds way of learning field IDs. I try to come up with them but it can be challenging. Might as well try:
Frullania nisquallensis LARGE AND LOOSE WITH ACUTE TIPS
Frullania bolanderi TINY AND APPRESSED WITH FLAGELLATE SHOOTS
Frullania californica SMALL WITH RUFFLED UNDERLEAVES
Frullania franciscana SMALL HYPERMARITIME WITH OCELLI
Frullania hattoriana MONTANE APPRESSED AND TINY
Frullania eboracensis DARK APPRESSED WITH DECIDUOUS LEAVES