How to know and photograph a liverwort

In the Pacific Northwest, there are more than 200 species of liverworts loitering in typically moist habitats. While identification can require microscopic examination, it is possible to get to species in the field or using photographs provided you shoot the right features. This post is intended for anyone who want to figure out their liverworts or wants help from others to do so. It will cover (1) how to recognize a liverwort and (2) how to photograph a liverwort in a way that increases probability of identification to species.

What is a liverwort?

Like mosses and hornworts, a liverwort is a plant where the life cycle is dominated by a persistent photosynthetic gametophyte that hosts a relatively short-lived and nutritionally dependant sporophyte (spore-bearing) phase. Liverworts can be leafy (see photos of Plagiochila porelloides and Porella navicularis) like mosses, but the leaves are always a single cell thick and they lack a mid vein. The leaves if liverworts also tend to be inserted in two ranks, 1 on each side of the stem, and frequently show a smaller leaf on the underside of the stem. Leaves of liverworts are frequently lobed, with those lobes varying in number and being equal, unequal, pointed, rounded and so forth. Mosses, by contrast have unlobed leaves that typically have a mid vein (“costa”) that consequently makes them more than one cell thick. Furthermore, moss leaves typically show leaves arranged all around the stem and of similar form and size.

The other group of liverworts is thalloid, having a continuous, frequently branching, flattened mass of photosynthetic tissues (see photos of Pellia neesiana and Marchantia polymorpha). What makes these liverworts? When sporophytes are present, their ovoid capsules open by longitudinal dehiscence, just as they do when present in the leafy liverworts. Within the capsules of both thalloid and leafy liverworts are odd little spring-like cells called elaters that expand and contract in response to moisture differences. Moss sporophytes by contrast lack elaters and open usually by a lid at their apices. Hornwort sporophytes have “pseudoelater” (that won’t help much in the field), and their exceedingly elongate capsules open by extensive longitudinal dehiscense lines (see Anthoceros fusiformis). The photosynthetic phases of both leafy and thalloid liverworts have cells that contain oil bodies, a feature that distinguishes this group from both mosses and hornworts.

How to photograph a liverwort

I often encounter great photos of liverworts on iNaturalist, but because they are limited to a single shot from a single perspective showing a single aspect of the plant, they are hard to interpret. By taking 15-30 extra seconds to photograph a few other features, you can take a mysterious liverwort and make it so that you and/or others can identify it at least to genus and often to species. The following shots are an ideal sequence:

(1) Habitat-a shot showing the liverwort in its environment— eg. Growing on a tree or along a soil bank. You can also just write this down in your observation notes that you upload with your photos
(2) Habit- a shot showing the whole plant with features like branching, orientation (is it upright? creeping? prostrate? Are sporophytes present?
(3) Shot of the upper side of the leafy plant or thallus to show leaf arrangement and general shape, presence and absence of pores et al. Could also possibly show developing antheridia, archegonia and sporophytes.
(4) Shot of the underside of the leafy plant or thallus. This will show features like underleaves, underlobes of lateral leaves, rhizoids, possibly developing antheridia, archegonia and sporophytes.
(5) Detail shot of leaf margin or upper thallus— the presence, absence, shape and relative size of lobes and teeth for leafy liverworts. For thalloid liverworts, this will show the presence and absence of pores and scales.
(6) If sporophytes are present, try and photograph them from above and below to show their relative size and surrounding leaves and structures (if present).

Obviously, shooting liverworts can be challenging on account of their size, but you can capture most of these things with a cell phone camera and magnifying glass/hand lens in the worst case scenario. I find picking a small sprig and holding it up to the sun or bright sky is particularly helpful in seeing finer details like leaf details (see photo of Ptilidium californicum).

Posted on December 29, 2022 08:27 PM by rambryum