Liverwort Trivia: Gymnocolea inflata versus Odontoschisma (Cladopodiella) fluitans

In an email, @gpalermo asked me about the ID of my observation https://www.inaturalist.org/observations/227068993, which I had called Gymnocolea inflata based on my (perhaps flawed) recollection of how we identified it in the field. In particular, why is it not Odontoschisma (Cladopodiella) fluitans? This sent me down a rabbit-hole of references which, in an attempt to justify spending time this way, I decided to share as a Journal entry. It turns out these two species are frequently confused, and there is no one good way to distinguish them.

Here's what I found for hints:

Blanka Aguero’s key to liverwort genera for our Maine course gives this separation:

• Leaf lobe incision up to 1/5 – ¼ of length….. Odontoschisma (Cladopodiella)
• Leaf lobe incision deeper, up to 1/3 – ½ of leaf length …. Gymnocolea inflata (and Obtusifolium)

Pope’s (2016) field guide sends these two in different directions with the couplet
-Underleaves present (includes Cladopodiella, for which he says “usually present near a stem tip”)
-Underleaves absent (includes Gymnocolea)
Pope's two species accounts don’t acknowledge a confusion, but he gives very different habitat descriptions:
Cladopodiella fluitans: Commonly collected in Sphagnum dominated peat bogs.
Gymnocolea inflata: Primarily a species of the boreal forest, the Arctic, and in high terrain, often in a succession situation, a pioneer colonizing seepy, noncalcareous rock surfaces.

The Flora of North America draft at https://www.mobot.org/plantscience/bfna/V3/ScapGymnocolea.htm and
https://www.mobot.org/plantscience/bfna/V3/CephaloziaceaeOdontoschisma.htm gives sketch images of each species, and, describes habitat thus:
Odontoschisma fluitans: acidophile, often with sphagnum in pools, less commonly on moist soil or rock; bogs, lake and pond edges, moist open areas
Gymnocolea inflata: igneous rock outcrops subject to at least periodic seepage, often in direct sunlight; also around rock pools and in bogs
FNA also states:
[Odontoschisma fluitans] sometimes confused with the more common Gymnocolea inflata. Odontoschisma fluitans may be easily identified if perianths are present. The perianths of O. fluitans, which are more elongate than the more globose perianths of G. inflata, do not become detached from the stem. Also O. fluitans does not develop terminal or lateral branches as does Gymnocolea. (The perianths are shown in the sketch images at the links above.)

British Bryological Society
https://www.britishbryologicalsociety.org.uk/wp-content/uploads/2020/12/Gymnocolea-inflata.pdf and
https://www.britishbryologicalsociety.org.uk/wp-content/uploads/2020/12/Cladopodiella-fluitans.pdf:
Gymnocolea inflata is characteristic of damp, acidic places, such as wet heaths, bogs and the edges of peaty pools. It can cover quite extensive areas of bare peat, and favours grazed peatlands and heaths. It also grows on non-base-rich shale, gravel or sand, as well as between rocks in block scree. Cladopodiella fluitans is often confused with G. inflata on peatlands, owing to its rounded lobes. Its leaves are relatively longer and narrower, but its diagnostic feature is the thread-like branches that stick downwards from the stem into the substrate.
and
Cladopodiella fluitans is “restricted to bogs and wet, peaty heaths.” Gymnocolea inflata is the same size and colour as C. fluitans and sometimes grows on peat in bogs, although it avoids the wettest pools. It differs in having shorter, wider leaves, as well as lacking thread-like branches, and often having inflated perianths.
The BBS also has some nice images at
https://www.britishbryologicalsociety.org.uk/learning/species-finder/gymnocolea-inflata/
and https://www.britishbryologicalsociety.org.uk/learning/species-finder/odontoschisma-fluitans/. To me, they emphasize that Gymnocolea leaves are cupped and O. fluitans leaves are flatter.

Lincoln (2008), Liverworts of New England, just mentions the two can be confused, but she shows sketches of the perianths as ID features.

So, my take-away for these is the following.

1. Look for perianths. If they are there, you can ID from those.
2. Consider habitat. If in Sphagnum bog, more likely O. fluitans. If more “successional,” G. inflata. But lots of overlap.
3. Branching. If terminal and lateral branches, Gymnocolea. If not, O. fluitans.
4. Look for underleaves (small, toward stem tip). If there, O. fluitans.
5. Consider leaf shape. O. fluitans has longer, narrower lobes cut shallowly, and leaves are flat or slightly concave. Gymnocolea has shorter, wider leaves cut deeply, and leaves are very concave.
6. If I were confident about the “thread-like branches,” I would look for those (O. fluitans).

With regard to the observation in question, https://www.inaturalist.org/observations/227068993, I went back to the original sample and re-examined it, finding this:

1. No perianths.
2. Habitat, on log in pond, didn't match either species well, but it wasn't a bog. (Gymnocolea?)
3. Branching. Yes. (Gymnocolea.)
4. Underleaves. I carefully examined six stems and found no indication at all of underleaves. (Gymnocolea?)
5. Leaf shape. I would say these leaves are longer than wide, shallowly incised, but strongly cupped. (flip-flop?)

6. Thread-like branches. Not sure what to look for, but none seen. (Gymnocolea?)
   At this point I would leave it at Gymnocolea, but I don't think it's at all certain.

I hope that list helps someone!
Janet Wright, July 6, 2024

Posted on 06 July, 2024 16:53 by janetwright