Monday, May 19, 2008

Standing on the corner

Hanging under the eaves of a garden shed, I found this abandoned flower pot:

Moss. And segregated; tall spore cases on the "front", short, flowering stems in "back". ("Back" and "front" defined by the photo, not by the round pot.)

What is it? Two species or one? I took a couple of dozen photos. At home, I consulted my Plants of Coastal British Columbia. A simple search, this time; it's the second entry under "True Mosses". Polytrichum juniperinum, Juniper Haircap Moss.

The two distinct expressions are sexual; the short individuals are male, the tall ones female.

So here are the males:

These upside-down umbrellas are the male "flowers" (properly called antheridia). They grow on a short stem with spiky leaves right to the base of the "flower". In this photo, you can see a couple of females who have invaded the male territory, but mostly they keep to their own company. This holds true to most populations of the Polytrichidae.

The female mosses have work to do; they can't just sit there and look handsome, like the males. After a rainy day, once sperm from the males has migrated across the wet surface and fertilized the young female plants, they develop sporophytes, long stems topped with spore cases.

The community forms three levels; at the bottom, the leaves, next the tall stalks and the ripe and empty spore cases. At the top are the capsules (sporangia) containing spores.

The leaves are folded towards their centre; if you look closely at the first photo, you can see the line where the two sides meet, and at the base of the leaf, the triangular gap between. This is a defining characteristic of the Polytrichidae.

The name, Haircap, or Polytrichum (many hairs), comes from another feature; the hairs that coat the capsule from bottom to tip. Look at this photo below full-size to get a good view of them.

The spores are formed inside these capsules, and held in by a lid, or operculum, the whole covered by the calyptra, the long-haired blanket that gives us the name.

When the sporophytes are mature, the lid pops open, displaying a toothed "mouth" (peristome); the spores are shot out of this when conditions are right.

Emptied, dried-up, wrinkled capsules.

More photos can be found at Biology 321, UBC, and Terry Thormin galleries.

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