Missouri has five species of starburst mosses (genus Atrichum). They tend to look different depending on whether they are wet or dry. When wet, they look like mass of bright green stars, but when dry, the leaves shrivel, contort, and look dead. We treat them here as a group, because separating them to species requires examination of tiny structures using a hand lens, microscope, or both.
With their acrocarpous (cushion) form, the stems don’t branch. They generally rise upward, together forming a cushion. The whorled, lance-shaped leaves look something like the tops of tiny pineapples — or from above, like little green stars. The leaves are attached at 45-degree angles. There are at least some teeth on the leaf margins. When dry, they curl and give the moss a dull, dead appearance.
An unusual feature of starburst moss leaves are lamellae (luh-MELL-ee). Lamellae are longitudinal strips of tissue, resembling thin blades standing on edge and extending parallel to each other along the midrib. Using microscopes, botanists can count the number of lamellae on a single leaf, and they can measure the height of the lamellae by counting how many cells tall they are. These characters are important for distinguishing the different species within this genus.
Sporophytes: The relatively long stalks and erect capsules are commonly bright red at maturity. While they are developing, the capsules are covered with a membranous cap or hood (calpytra) that lacks hairs, has a pointed beak, and is split lengthwise from the base. The calpytra falls away when the spores are ready to be released, usually in early spring.
Learn more about Missouri’s mosses on their group page.
At least five species of starburst mosses have been recorded for Missouri. Two are widespread and commonly encountered; three are less common. Here is a brief introduction, with some ID tips:
- Wavy starburst moss (A. altecristatum) is named for its undulate (wavy) leaves (that is, the leaf blades look something like lasagna). The leaves reach 1.5 mm wide, which is relatively wide. It looks very similar to slender starburst moss (A. angustatum), which has wavy lamellae, while wavy starburst moss’s lamellae are straight, on undulating leaf blades. With a microscope, it’s easier to see ID characters like the number of lamellae (usually 4–6), and various characters of cells. Common and widespread in the eastern United States, occurs in a variety of soil habitats, including overgrazed woods.
- Slender starburst moss (A. angustatum) has leaves less than 1 mm wide at midleaf; it’s the only one with such slender leaves. The leaves appear channeled, with the lamellae comparatively numerous, tall, and wavy. With the naked eye, what appears to be the “midrib” accounts for more than 1/4 of the width of the leaf. With a microscope, it’s easier to see ID characters like the number of lamellae (usually 6–9), and various characters of cells. It is another common and widespread species; it is especially common on mounds of soil thrown up by the root of fallen trees. Often on acidic, dry soils, often in rather large colonies.
- Strongly crispate or strongly crisped smoothcap moss (A. crispulum) is robust (approx. 2 inch tall), large, green to dark green, becoming brown or rusty with age. Leaves broad, undulating, with only 4–6 lamellae that are relatively low. Often is matted, well up the stem, with whitish rootlike rhizoids. Resembles a much larger version of A. altecristatum, roughly twice its size. Lives in shady, wet places in undisturbed native plant communities, such as stream banks and edges of fens and swamps.
- Crispy smoothcap or crispate smoothcap moss (A. crispum) is usually yellowish green; leaves not wavy, with lamellae 1–3 or lacking, often discontinuous. Slightly smaller than A. crispulum. Lives in intact native plant communities: in shady places in sandy soils along streams and ditches and at the edges of wetlands.
- Cylindrical atrichum (A. cylindricum) is dark green and densely leafy. It is similar in size to A. crispulum, but A. cylindricum is not dioicous (most shoots are female, with male-only shoots not reported); also, its leaves are more slender and less wavy than A. crispulum. Compared to A. altecristatum, A. cylindricum has shorter lamellae that are strictly parallel, and its leaves are longer, more slender, and not wavy. In Missouri, apparently confined to swamp habitats in the Bootheel.
Similar species: Starburst mosses (genus Atrichum) are among several genera in family Polytrichaceae. Members of this family are acrocarpous (nonbranching, bearing capsules only from tips of stems), generally erect in habit, with leaves that have a midrib with lamellae.
In addition to Atrichum, other Missouri genera in family Polytrichaceae are Pogonatum (2 spp.) and Polytrichum (5 spp.).
- Members of Polytrichum, called haircap mosses, tend to be larger mosses, with more opaque leaves, which are often at a 90-degree angle to the stem, with brown, pointy tips; also, their pointy capsule caps are covered with woolly hairs. Juniper haircap moss is a common representative.
Another common Missouri moss, the tiny tornado moss (Tortella humilis) is similar to starburst mosses, and its leaves also curl and contort when dry. But it is tinier and lacks lamellae and teeth on the leaves.
Height can be helpful for distinguishing the species. The two common species are shortest, with A. angustatum having stems 1–2 cm (about ½ inch) high, and A. altecristatum having stems 1–3 cm high. The other three species reach 5 cm (2 inches) high, with A. crispulum reaching 6 cm (2¼ inches) high.
Two species occur statewide; our other three have limited distributions.
Habitat and Conservation
Members of this genus are especially common on bare or disturbed soil, like that in the ditches along roadsides. Slender starburst moss (A. angustatum), as noted above, is especially common on the loose mounds of soil raised up by the roots of trees that have pitched over.
Our three less common species are rarer and only likely to be found in undisturbed natural habitats.
Status
Of our five Atrichum species, two are widespread and commonly encountered: the wavy starburst moss (A. altecristatum) and the slender starburst moss (A. angustatum).
The other three are Missouri species of conservation concern, ranked as imperiled (A. crispulum) or critically imperiled (A. crispum and A. cylindricum).
Life Cycle
As with other mosses, starburst mosses have 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. Most Atrichum species are dioicous: the sperm- and egg- producing structures are found on separate gametophyte plants, meaning that the gametophytes are either male or female. You can identify the male mosses because they have “splash cups” that look like tiny flowers at the stem tips; sperm develop in the centers and can be dispersed via rainwater.
When water, even a thin layer of rainwater, is present, the sperm can swim to the eggs (in the female organs of mosses) and fertilization occurs. The resulting offspring plant, called a sporophyte (spore-bearing plant), grows out of the female organs of the gametophyte.
The sporophyte, in this genus, takes the form of an erect, long-stalked, cylindrical capsule growing out of the tip of the gametophyte stem. It obtains nutrients from the gametophyte. A pointy-tipped calyptra with a slit in its side sheaths the top of the capsule as the sporophyte matures. When mature, the capsule opens to release spores, which can grow into new gametophyte plants. In most starburst mosses, the capsules mature in fall and early winter and open in early spring. Gently tap a mature capsule, and you’ll see a puff of spores waft out.
Mosses also commonly reproduce asexually when a portion of the plant breaks away, gets moved elsewhere, and continues growing as a separate plant.
Human Connections
The genus name, Atrichum, means hairless (a-, meaning “without”; -trichum, meaning hair); it refers to the hairless calyptrae that look like tiny pointed caps atop the maturing capsules. It explains the common name “smoothcap mosses.” This is a contrast to the related genus Polytrichum, the “haircap mosses,” whose name means “many hairs” and whose capsule-tops typically are covered with woolly hairs.
These mosses are still sometimes called “Catharinea mosses,” as in “wavy Catharinea,” “slender Catharinea,” and so on. At one time, genus Atrichum was called Catharinea, in honor of Catherine II, called Catherine the Great, 1729–1796, who was the empress of Russia from 1762 to 1796. In her long career as a major world leader, Catherine was a patron of the arts, literature, education, medicine, and the natural sciences. She helped bring Enlightenment thinking and European intellectualism to Russia. Many early botanists relied upon the patronage of royal families to subsidize their work, so patrons were often rewarded by having a plant named in their honor.
Ecosystem Connections
Compared to pleurocarpous (branching or carpet) mosses, acrocarps are less likely to be used as nesting material in bird nests. However, the cushions and miniature forests of stems provide habitat for many kinds of small animals, including springtails, sowbugs, worms, insects, snails, centipedes, salamanders, and small snakes. Birds and other animals look for prey among these lush, miniature habitats.
Many mosses, including our two most common starburst mosses, grow on disturbed soils, such as overgrazed woodlands and the tip-up mounds created by trees that have fallen over. By colonizing bare soil, they help prevent erosion, and help other, more sensitive plants survive.
While many mosses tend to be found in colonies of only their own species, colonies of our common starburst mosses often include other types of mosses, which intermingle with the loose tufts of the starburst moss. Tooth mosses (Plagiomnium spp.), for example, often live among starburst mosses. Tooth mosses are distinctive with their trailing stems with oval, clear, two-ranked leaves, and their nodding capsules, while starburst mosses have upright stems, narrow, whorled leaves, and erect capsules.
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.