Porella liverworts, often called scaleworts or wall scaleworts, are fairly common Missouri species of leafy liverworts. The three Missouri species in this genus are rather large and vigorous — compared to most other leafy liverworts. Porellas have a leafy look and have numerous branches, giving them a crowded, matlike appearance. They grow flat against the trees or rocks they live on. The leaves are rounded, alternate, and arranged in two rows along the stem. Porellas are often brighter green than frullanias such as the very common New York scalewort. As with other leafy liverworts, these mossy-looking liverworts have leaves in two apparent rows, distinguishing them from true mosses, whose leaves are typically whorled.
Liverworts, like mosses, are land plants that do not have a vascular system. Their lack of veinlike tubes to conduct moisture and nutrients throughout the plant limits them to a small size. They produce spores instead of seeds. Their form of reproduction usually requires them to be in wet or moist places.
Learn more about liverworts on their group page.
To identify liverworts to species, specialists examine details of the plant’s reproductive structures. Unfortunately, the reproductive structures of leafy liverworts are obscure, variable, and hard for an amateur botanizer to see.
Missouri has three species of scaleworts in genus Porella:
- Pinnate scalewort (P. pinnata), whose leaves are relatively small and barely touch or overlap
- Wall scalewort (P. platyphylla)
- American wall scalewort (P. platyphylloidea), whose leaves are larger, more crowded, and overlap, giving it the gathered appearance of a raised curtain.
Similar species: Missouri has about 36 genera of leafy or scaly liverworts.
Leafy liverworts are often mistaken for mosses, perhaps because few people know that liverworts can have this tiny leafy or scaly form.
Width: Most leafy liverworts only cover an area up to about 4 inches wide; the width of an individual stem of a leafy liverwort, including the leaves on both sides, is usually no more than about 1/16 inch (2 mm) wide.
Statewide.
Habitat and Conservation
Porella species may be found on rocks or on tree trunks. Leafy liverworts generally occur in moist or wet, cool, shady places such as along stream banks, on the terraces above streams, cool valleys on the north sides of slopes, and so on. They usually grow on a solid surface such as rocks or tree trunks, often close to the ground. Certain species are associated with particular substrates and habitats.
Status
Although porellas are some of the more common leafy liverworts in Missouri, few people notice them or understand what they are seeing when they see one.
Life Cycle
Unfortunately, the reproductive structures of these and other leafy or scaly liverworts are too tiny and obscure for most amateurs to see. As with other liverworts and mosses, porellas have an alternation of generations: the plant we usually think of as the scalewort is a gametophyte, which has organs that produce gametes (sperm or eggs; different plants are male and female). The gametes unite and give rise to a sporophyte, technically a separate plant. It grows out of the female organ of the gametophyte. At maturity, the capsules release spores that can become new gametophytes.
Like other liverworts, porellas can also reproduce asexually by cuttings, when a portion of the plant is severed from the rest and moved to a new location. In addition to mechanical cutting, this type of asexual reproduction also commonly happens as the young stem tips continue to grow and the older sections of stem die off and decompose, meaning that the stem tips become independent new plants.
Human Connections
Who cares about such tiny plants, when it takes so much work to identify them, and you have to learn so many new terms? It’s human nature to distinguish between things, and to apply names to them. It’s one of the first tasks humans did in the Bible, and it’s a basic human survival skill. Children take to it naturally, and most of us like to “geek out” about something.
Now is a great time to learn about liverworts and mosses, because there is so much information available online. Before the Internet, you needed access to heavy reference manuals and scholarly journals, whose pictures were limited by publishers’ budgets. Today, photographs abound, and information is available at all skill levels.
Ecosystem Connections
A variety of microscopic and near-microscopic invertebrate animals — such as mites, water bears (tartigrades), and roundworms — are associated with liverworts and mosses, but little is known of the effects these organisms have on each other. Compared to our knowledge of pollinating or plant-eating insects and flowering plants, the amount we know about these smaller organisms is very limited.
In spring, many birds hunt in woodlands for soft, fibrous nesting materials, and liverworts and mosses are certainly among those used. Prothonotary warblers have been recorded using leafy liverworts in nest construction.
Mosses, liverworts, hornworts, and lichens seem rather similar, but these organisms are in very different groups. Mosses, liverworts, and hornworts are small, low plants usually found in damp habitats. Unlike more familiar plants, they lack veinlike structures and do not produce flowers or seeds — instead, they produce spores. Meanwhile, lichens are not plants at all: they are a collection of different fungi that have photosynthetic algae living within their tissues.