Frullania in the Pacific Northwest

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

Species	Habitat	Habit	Size	Dorsal Lobe apex	Ocelli Present	Underleaf margins	Diagnostic features
Frullania nisquallensis	Predominantly epiphytic, especially alder	Loosely overgrowing, occasionally appressed	Large	Acute	scattered	reflexed	Acute apices on Dorsal Lobe
Frullania bolanderi	Epiphytic in riparian and lacustrine environments	Tightly appressed to substrate	Tiny	Round	absent	flat, toothed	Flagellate shoots
Frullania californica	On rock and trees	Loosely appressed	Small	Round-Obtuse	irregular, scattered	ruffled	small with ruffled underleaves
Frullania fransciscana	On coastal rock	Loosely appressed	Small	blunt-acute;	forming line	flat	hypermaritime with ocelli in line
Frullania hattoriana	mid-montane epiphytic on conifer trunks	Tightly appressed to substrate	Tiny	Round;	absent	flat, toothed	mid-montane appressed
Frullania eborecensis	Epiphytic & Epilithic	Appressed	Large	rounded	absent	?	Deciduous leaves ("cauducous")

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