Liverworts and Hornworts of New Brunswick

This website is home to the checklist of the liverworts and hornworts of New Brunswick. It is intended to serve as an easily accessible resource for scientists and laypeople who wish to know more about the tiny plants that often go unnoticed throughout our province. This website compliments our peer-reviewed academic publication of the same name (Haughian et al. 2016). Students and professionals wishing to cite our work should refer to the latter.

What is a Checklist?

In biology, a ‘checklist’ is a published and annotated list of species within a defined geographic area. Most commonly, checklists represent a restricted subset of the total species diversity (e.g., birds, trees, amphibians), because the author of the list has expertise that are limited to that particular subset. Checklists usually represent the first step towards developing a more extensive tool such as a flora, which would include more detailed descriptions of species, keys to identification, or ecological information.

What are Liverworts?

Liverworts are tiny plants; in fact, ‘wort’ is an old-English word for ‘plant’. The ‘liver’ part of the word comes from observations that the surface texture of some of the first-named liverworts looked much like that of a mammalian liver. Another term used to describe them, ‘hepatic’, also refers to this resemblance. In actuality, only a small number of the estimated 9000 species do resemble a liver (e.g., Conocephalum conicum), but the name has stuck. The scientific name for the group is Marchantiophyta, and it is considered a ‘subdivision’ of division Bryophyta within kingdom Plantae. This subdivisional classification should probably be upgraded to division, as recent evidence has shown that other bryophytes (mosses and hornworts) actually have independent origins from liverworts, and are no more related to liverworts than grasses, ferns or pine trees. Nevertheless, liverworts, hornworts, and mosses share many structural characteristics, and so are still often lumped together as the Bryophyta for convenience.

Like mosses, liverworts are non-vascular, meaning they don’t have internal water-moving tissues; in contrast, trees, grasses, herbs, and most of the large plants that we interact with directly are vascular, meaning they have roots to collect water, and stem tissues to move water to the tips of their leaves. Because liverworts can’t move water from the soil to their leaves, they rely on atmospheric water (mainly rain or fog) to stay wet. Staying wet, for at least part of the time, is important, because water is required for photosynthesis, and photosynthesis is necessary to stay alive and grow.

Although liverworts don’t have roots, they do resemble larger plants in some respects. They have rhizoids (which is a scientific word meaning ‘root-like things’), that help them to stick to the surface they are growing upon. Many liverworts (those of the class Jungermanniales) also have phyllids (a scientific word meaning ‘leaf-like things’), that are made up mostly of photosynthetic cells (cells containing chloroplasts, which is where photosynthesis actually takes place). Both of these organs tend to be one cell thick. The caulids (stem-like things), on the other hand, tend to be several cells thick.

Some liverworts, however, lack clearly defined phyllids and caulids. Instead, they are what we call ‘thallose’ liverworts (classes Marchantiales and Metzgeriales). Thallose liverworts look like a plant that has been squashed down into 2 dimensions. Instead of a stem with leaves, they look like a single large leaf, or a stem with a continuous green membrane along each side.

Like other members of the Bryophyta, the main body of the liverwort is what we call a gametophyte phase, meaning it is haploid and produces gametes. But what makes them different from other plants isnot that they have a gametophyte phase, but that the gametophyte phase is dominant and free-living in the life cycle. In contrast, the main body of a vascular plant (like a carrot) is diploid or polyploid; only specialized organs (e.g., ovaries or anthers) produce gametes, and those organs are completely dependent upon the sporophyte for their energy. In liverworts and other Bryophyta, the opposite is true: the sporophyte phase is dependent upon the gametophyte for energy. In general, the sporophyte phase in liverworts is represented by a stalked organ that grows out of the main body, and produces spores from a small capsule at the tip.

What are Hornworts?

Hornworts are another of the groups of tiny plants that are lumped together in division Bryophyta. The scientific name for their subdivision is Anthocerophyta – a name derived from the ancient Greek words anthos (bloom or blossom) and ceros (horn). This descriptive name refers to the spore-producingorgans of the hornworts, which look like horns or antlers.

Hornworts are superficially similar to thallose liverworts, but differ in some important ways. First, they have only a single large chloroplast in each photosynthetic cell. Liverworts, mosses, and vascular plants all have multiple chloroplasts. Second, their sporophytes grow from the base, rather than the tip. Third, like mosses, they have stomata (little gas-exchanging pores) on their spore-capsules. Another common feature in hornworts is that they tend to be symbiotically associated with cyanobacteria, although some liverworts also have a primitive association of this type.

Far less is known about hornworts than liverworts or mosses. There are about 300 named hornwort species, but very few occur in boreal and temperate regions, and those that do grow primarily on muddyor silty banks and shores. Because of this combination of wet habitat, small size and short duration of sporophytes, most Canadian hornworts could be easily mistaken for a smear of algae at first glance.

Collecting liverworts and hornworts

Example herbarium packet label: