Apple #412: Moss

After that last, somewhat steamy entry, I thought it was time for something nice and soothing. Like moss. Mosses are so soft and springy and spongy and green.


(Photo by the Apple Lady)

• Mosses grow everywhere on the planet except on the sea floor.

• There are so many different kinds of mosses and their parts are so tiny, the only way to identify them accurately is with a microscope.

• Mosses are Bryophytes. The reason we care about that word is because it means they were the first green plants to evolve on land.

• That makes mosses about 350 million years old. Older than flowering plants, older than conifers.

• As the first green plants, mosses were very simple, and they have stayed simple. They have no stems, no roots, and no leaves in the sense that we think of them.

• Without typical roots and stems, mosses don't have a vascular system, or a way to deliver moisture & nutrients to all parts of the plant. So mosses depend on their environment to supply the entire plant with adequate moisture and nutrients.

• In other words, mosses prefer to live in moist places. They are very inventive at finding places where enough moisture collects.

WHERE MOSSES LIVE

• In the northern hemisphere, mosses like to grow on the north sides of trees. You might see moss growing all around the base of a tree, but you'll see more of it on the north side.

• The reason mosses like the north side is because less sunlight shines over there. That keeps the north side relatively shady and damp, a nice home for a moss.

Apparently the right half of this tree is to the north. That whole side is covered in moss while the other side is nearly free of it.
(Photo by the Apple Lady. Sorry about the blurring.)

• Some other places that mosses especially like:

• Up the sides of hardwood trees. They collect the rainwater as it trickles down the crevices of the bark.

Moss growing in a nearly perfect vertical stripe.
(Photo by the Apple Lady)


On this white ash tree, moss is also growing in the bark crevices on the roots.
(Photo by the Apple Lady)

• On fallen logs and stumps. The nooks and crannies in fallen logs make them ideal spots for mosses. Water collects there as do other nutrients. The mosses that live on fallen trees don't even need to take any nutrients from the fallen tree itself (which means they're epiphytic).
  

Moss growing all along the top of this fallen tree trunk.
(Photo by the Apple Lady)

• Rooftops. Shingles made of wood or composites or even asbestos make a friendly place for the mosses to sit. Ash that flies up from the fireplace provides nutrients, and if it's nice and shady up there, the roof doesn't dry out so fast and the mosses like it even better. At my parents' cottage by a lake, it's one of our fall tasks to climb up on the roof and sweep off all the moss pillows. Now I know why we get so many moss pillows up there. That roof has all the ingredients that mosses like best.

Moss pillows growing out of the cracks between shingles.
(Photo by Holly Holston, age 14)

• Sidewalk cracks. The cracks collect nutrients and moisture that isn't easily dried up by sunlight. Again, a naturally happy place for mosses to grow.
  

Moss growing in the crevices of a sidewalk in Cotacachi, Ecuador.
(Photo by Gary A. Scott)


Moss growing like mad all across the surface of a sidewalk.
(Photo by Sean Dreilinger on Flickr)

• Some mosses can ferret out even the tiniest cracks in cement so it seems almost as if the cement is the moss' soil. This can make cement walkways very slippery. For suggestions about how to control such slippery moss, see Oregon State University's reluctant suggestions for moss control.
  

MAKING MORE MOSSES

• When it comes to reproducing, mosses are again dependent on their environment, but for this function they need wind as well as moisture.
  

• Male mosses produce zoospores. The male mosses fling their zoospores out and the wind carries them off. Some of the zoospores land on a female moss. The zoospores and the egg cells on the female moss will try to get together, but they'll only be successful if there's enough moisture.

• Once the female plant's eggs are fertilized, she shoots up a stalk, also called a seta or a sporophyte. At the top of the stalk is a little knob or a pod, called a capsule.

Female moss reproductive structure
(Diagram from Oregon State University)

• The capsule contains single-celled spores. They're sort of like tiny seeds, but they're even biologically simpler than seeds. When the female plant decides the moisture and wind and all those conditions are right, the capsule opens and the spores fly off on the wind.

• The spores might land anywhere, but again, they need enough moisture to become a plant.

MOSS IMPOSTORS

• Some things get called mosses but they're not really.

• Spanish moss -- not a true moss. It produces flowers and it's a Bromeliad, like a lot of houseplants. It also happens to be epiphytic, which means it grows on another plant but doesn't take any nutrients from it.

• Club moss -- Ground Pine might be a more accurate name. These are an evergreen herb.
  

• Flowering moss -- if they produce flowers, we know they can't be a true moss. Better known as Creeping Phlox.

• Reindeer moss -- actually a type of lichen, which is like the marriage of a fungus and algae.

MORE REASONS TO LIKE MOSS

• Besides the fact that they're soft and springy and green, we like mosses because they help prevent erosion. By hanging onto the soil, they help prevent it from being blown or washed away. At the same time, they help to increase the amount of moisture that the nearby ground is able to store.

• They are also good indicators of pollution. Or rather, their absence is. There are so many different kinds of mosses and they're so good at finding little nooks and niches where there's water and nutrients, if you don't see any around, chances are you're in a place where there's lots of pollution.

With all this moss growing like a carpet along the gravel path, we know we don't have to worry about air pollution here. And if we felt like it, we could take off our shoes and the moss would feel so nice underfoot.
(Photo by the Apple Lady)


Sources
Oregon State University, Basic Biology of Mosses
US Forest Service, Pacific Northwest Research Station, Special Forests Products Bryophyta (division) Moss, 2001
Wise Geek, What is Moss?
Backyard Nature, Mosses
Indiana Public Media, A Moment of Science, There's Moss on the North Side, September 27, 2003