Excerpts from Jim Conrad's
Naturalist Newsletter

MNIUM'S ANTHERIDIAL HEADS

from the July 26, 2009 Newsletter, describing a backpacking trip on the Pacific Crest National Scenic Trail in Red Buttes Wilderness Area, Siskiyou County, California:
MNIUM'S ANTHERIDIAL HEADS
Here and there across Kangaroo Spring's broad meadow foot-wide streams of black, cold water slowly flowed in channels sunken a few inches below the sod. The vertical-walled channels usually were so well hidden by tall grass and wildflowers that if you didn't watch you could step right into them. Usually the channels' wet rims were mantled with carpets of tiny, closely packed mosses, many doing the special thing you can see above.

I think but am not sure that the moss shown belongs to the genus MNIUM. You know that mosses reproduce by spores, and that the spores are released from capsules set atop hairlike stems called setae. So, what are the rusty-colored, flat structures situated where the capsules' setae should be rooted?

Those are pinhead-size "antheridial heads." Antheridia produce male sex germs, or sperm. The idea is for sperm from antheridial heads to reach female sex germs in narrower "archegonial heads" growing elsewhere.

I've read two explanation for the antheridial heads' structure and both explanations need water in the cups. One account has raindrops hitting the heads, splashing sperm out of the cups to where female sex germs in archegonial heads await them. Another idea says that the sperm are coated with a little fat, form a very fine scum atop water in the cup, then insects wandering across the moss-carpet surface get sperm stuck on their legs and transfer them to archegonial heads.