Widespread globally, urn moss, or goblet moss, top moss, or common bladder moss has distinctive, light green sporophyte capsules that are shaped like upside-down pears. It often occurs in open, sunny, disturbed places, such as margins of crop fields, roadsides, and gardens.
The gametophyte of this moss is very obscure, with tiny, light green, bladelike leaves that twist when dry. It forms small tufts about the size of a cat’s paw, and it often occurs in scattered, small patches. For a rather tiny moss, the sharp-tipped leaves are relatively large, oblong-lance-shaped, about 2–3 mm long, apparently untoothed to the naked eye (frequently toothed toward the outer tip but difficult to see without magnification), with one midvein.
The sporophyte of this species is easy to identify. When young, the capsules are spherical, large in relation to the moss, and light green like a gooseberry. The capsules are held erect and are borne on golden to brownish-red or rusty stalks that are about 0.5–1.5 cm (3/16 to 5/8 inch) long. The capsule is tipped with a beak, which is itself covered with a calyptra (capsule lid) that has a much longer tip. Old capsules, when dry, are shaped like spittoons (or urns, or flower vases) — restricted around the open mouth, which typically turns darker brown.
Learn more about Missouri’s mosses on their group page.
Similar species: Three other species in genus Physcomitrium have been recorded for Missouri; none of them, however, are as widespread and common as P. pyriforme:
- P. immersum has its capsules immersed — that is, they are hidden or completely overtopped by the leaves surrounding them.
- P. collenchymatum is smaller than P. pyriforme, with capsule stems only 2–3 mm high, and it has the mature (open) capsules shallower and wider-mouthed; it is a species of conservation concern in Missouri, ranked as critically imperiled.
- P. hookeri is another species of conservation concern in Missouri, ranked as “SU,” meaning it is unrankable due to lack of information about its presence in the state. Its leaf margins are entire (toothless, even using magnification). Botanists note that the cells ringing the capsule mouth are large, inflated, and can roll away or fall off as a ring, mostly falling away.
Missouri has 5 other members in the family, but in different genera: Aphanorrhegma serratum, Funaria flavicans, Funaria hygrometrica, Physcomitrella patens, and Pyramidula tetragona.
Beginners might confuse urn moss with the following widespread mosses with rounded capsules:
- Woodsy moss, baby tooth moss, woodsy thyme moss, or toothed plagiomnium (Plagiomnium cuspidatum) is widespread in Missouri. Its leaves are toothed and are two-ranked, growing from two opposing sides of the stem. Its chubby, keg-shaped capsules arise on stalks in early spring but they are nodding (bent downward) (not held erect).
- Green-cushioned weissia, or controversial weissia (Weissia controversa), is another widespread, small cushion moss that typically occurs in disturbed, sunny areas. When dry, the narrow leaves curl like pigtails. When moist, the leaves’ outer sides are inrolled upward. Its sporophytes are usually seen in spring and are football shaped, shaped like an elongated egg, or cylindrical. Their stalks are only about 3–8 mm long (only to about ¼ inch).
Height: sporophyte stalks to about ½ inch tall. Width: an individual patch of this moss is usually only a few inches wide.
Statewide. This moss has a wide distribution globally.
Habitat and Conservation
Although we usually associate mosses with moist, shady areas, urn moss typically occurs in open, sunny, disturbed places, such as margins of crop fields, pastures, roadsides, lawns, and gardens. When it dries and the leaves curl and contort, the small patches of this moss are easy to overlook. But when it forms its tiny green, top-shaped capsules in spring, it is one of the easier mosses to identify.
Life Cycle
As with other mosses, this species has alternating generations. The plant we usually think of as the moss is the gametophyte generation (it’s a gamete-, or sex-cell-bearing plant). In separate organs, it produces sperm and eggs. When water, even a thin layer of rainwater, is present, the sperm can swim to the eggs and fertilization occurs. The resulting offspring plant, called a sporophyte (spore-bearing plant), grows out of the female organs of the gametophyte. In this species, the sporophyte takes the form of a stalked capsule growing out of the tips of the gametophyte stems. It obtains nutrients from the gametophyte. When mature, the capsule opens to release spores, which can grow into new gametophyte plants.
Mosses also commonly reproduce asexually when a portion of the plant breaks away, gets moved elsewhere, and continues growing as a separate plant.
At the base of the moss you may see a tangled network of tiny, threadlike green filaments called the protonema. The protonema is the juvenile form of the gametophyte (which is what most people would think of as the “moss plant”); it is the first outgrowth of the germinating spore. The protonema produces buds from which the more familiar, larger gametophyte grows. Having visible protonema is not unique to this species, but we point it out because it is often visible at the base of the small tufts of this moss at fruiting time.
Human Connections
The genus name, Physcomitrium, apparently comes from Greek physo, referring to a bladder, bellows, or air sac, and Latin mitra, meaning a cap or turban — put together, they describe the bubble-like turbans or urns of the sporophyte capsule.
Ecosystem Connections
This and other mosses help prevent erosion. They also provide a microhabitat for springtails, mites, and other tiny animals — even along roadsides, disturbed pastures, and the margins of crop fields.
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.