Tuesday, December 14, 2010

Don’t call me Moss, sir!

The other day, I wrote about moss popping up in our yard. In my original post, I had a photo of something that superficially looks like a moss, but really isn’t. Instead, it’s a lichen.

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Lichen on rock in our back yard

Moss, lichen—they all grow on rocks and trees, so how big can the difference be? To my amazement, I realized that the difference is fundamental.

Mosses, even though they don’t have roots or flowers, are real plants with tiny stems and leaves. They prefer moist and dark areas and form mounds or mats that are soft to the touch. When no water is available, mosses dry up and can survive in that state for quite some time.

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Tree moss (Isothecium myosuroides) in the Hoh Rain Forest, Olympic National Park, Washington

Lichens, on the other hand, are composite organisms consisting of a fungus living in a symbiotic relationship with a partner that is capable of photosynthesis (either an algae or a cyanobacterium). I like how lichenologist Trevor Goward describes it: “Lichens are fungi that have discovered agriculture”.

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Green and red lichen, Cradle Mountain National Park, Tasmania

Unlike mosses, likens are less dependent on a steady supply of water and hence look more or less the same year round. They can survive in climatic extremes, like arctic tundra and hot deserts, but are also found in more temperate environments, sometimes even in the same place as mosses. (For a fascinating article on lichen, check out this post by fellow garden blogger Alan Lorence.)

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Lichen and moss on boulder and tree, Yosemite National Park

For a layperson (like me), it’s sometimes difficult to distinguish between lichen (fungi + algae) and straight algae. I wasn’t sure if the orange-red in the next two photos is from lichen and algae, but it seems to be algae (specifically a green algae with “abundant orange secondary pigments forming a shaggy coat”).

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The entire side of this house is covered by algae; this is actually the fog signal building at Point Reyes National Seashore north of San Francisco
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Lichen (white) and algae (orange-red), Point Reyes National Seashore, Northern California

The green stuff covering the rocks and pilings in the next photo is algae as well.

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Algae-covered rocks, La Push, Washington

It’s safe to say that the only place most gardeners will ever encounter algae in their yard is in a pond or other body of standing water. Unless they have water-front property, that is.

Another plant often confused with moss is “Spanish moss” (Tillandsia usneoides). Not a big surprise considering that “moss” is part of the name. Actually, Spanish moss is an epiphytic bromeliad. “Epiphytic” means that it grows on another plant, such as a tree, and extracts all its nutrients from the air and rain. Bromeliads include house plants such as billbergias and guzmanias; dyckias and hechtias popular in xeriscaping; as well as the common pineapple.

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Spanish moss (Tillandsia usneoides) in Louisiana
Photo from Wikipedia

Spanish moss only grows in areas where the climate is sufficiently warm and humid, such as the southern and southeastern U.S. In fact, when I think of Spanish moss, pictures of stately antebellum mansions with oak-lined avenues come to mind. Spanish moss prefers southern live oak (Quercus virginiana) as well as bald cypress (Taxodium distichum), another iconic tree of the South, because the leaves of these trees leach minerals that serve as nutrients for Spanish moss. It hangs from trees like a long silvery beard and can form quite a sizable mass.

I think Spanish moss looks utterly beautiful; it creates a wistful and brooding atmosphere that brings to mind Gone with the Wind and other tales of days long gone by.

3 comments:

  1. I'm really likin' this post! =D

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  2. I tell you, I learned a lot in a short period of time while doing a few quick Google searches.

    I have great photos of antebellum plantations in Louisiana but cannot for the life of me find my slides from 1998...

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  3. Love the lichens, esp. the photo with the lichens covering the side of the building.

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