Macro Monday: Moss

Take a glimpse into this tiny strange world on top of a brickbat.  Also check out what other tiny worlds people are photographing for Macro Monday, hosted by Lisa's Chaos.

In an out-of-the way spot on the north side of my house is a shady, damp place where I put plants I bought or divided while they wait to be planted in the ground.  There's also a handful of brickbats that I used to mark a spot where I occasionally stick cuttings so I don't lose track of them.  (Brickbats are just broken bricks.  If I had enough I might make a crazy-quilt brickbat path like some of the ones in the gardens in Colonial Williamsburg.) I guess it's very damp and shady indeed, because I found a happy healthy colony of mosses.

I know very little about moss and about all I do know I learned about five minutes ago in Brian Capon's Botany for Gardeners.  The little brown stalks are part of the moss's reproductive cycle.  Actually, it's weirder than that, because they are totally separate plants.  When you first notice moss in your garden, it may be just a soft green mat with no little brown stalks.  The green moss is a collection of both male and female plants.  These plants are unusual because they are haploid, meaning they have only one copy of chromosomes in the cells.  You may recall from high school biology that human body cells have pairs of chromosomes and so are diploid, but that human sperm and egg cells have only a single copy of each chromosome.  Those are haploid cells.  Mosses are a bit different.  The green part of the moss consists of plants that are entirely haploid.  These are the gametophytes, whose job is to produce gametes: sperm and eggs.  The sperm sit in "splash cups" on the males and are splashed onto neighboring females by raindrops.  Moss sperm cells actually "swim" to the eggs through water.  It's only when the sperm and egg get together that a diploid cell (the zygote) is formed.  This is the beginning of a new stage of the life cycle of the moss.  The zygote splits by cell division to form another plant, called the sporophyte.  The job of the sporophyte is to form spores.  In fact, it doesn't even photosynthesize so it draws food from the female gametophyte it's attached to, but it is a separate plant.  These sporophytes are the small brown stalks sticking up out of the green moss.  The spores form in the structure at the top and then disperse to start new colonies.