l

liverwort and pearlwort: 2 weeds of my driveway and cracks-and-crevices

ONE OF “perhaps the most primitive plants still in existence” and another that is a relative of Irish moss are two tenacious and odd-looking little creatures that like to inhabit my driveway and other crack-and-crevice spots. Maybe you have liverworts (above) or birdseye pearlwort at your place, too?

You know me: I like to know my weeds—rather than just have a fit about some infestation or other, to actually find out what they are, and where they are native to, and what their role for better or worse is in the bigger picture is (other than to irritate me).

I don’t know which liverwort I have, but it is what’s called a thallose species—made up of flattened tissue that looks almost rubbery to me. You might think at first they were some kind of moss or algae, and in fact like those other Bryophytes the liverworts have no vascular system, and they reproduce by spores.

Liverworts are “perhaps the most primitive plants still in existence,” says the Slater Museum of Natural History at University of Puget Sound in Tacoma, Washington.

One such thallose liverwort, the globally widespread species Marchantia polymorpha (above video), is a familiar problem on container plants in nurseries, on the potting-soil surface. It loves the moist environment with ample fertility. You may have purchased a nursery pot with this in it—look familiar?

“These plants without roots or vascular tissues for nutrient transport are living links to the transition from the algae that found its way out of the ocean to the established multitude of land plants,” says the Joint Genome Institute at Lawrence Berkeley National Laboratory, which created the video.

Liverworts are an important organism of their native habitats, but as for mine growing in the gravel here, probably not so much. They’re hard to get rid of, though, since undetectable spores are probably everywhere. I think changing the soil environment and watering practices in those spots to be less moist and conducive to their propagation is more the ticket, as Oregon State recommends to nurseries troubled by it.

MY OTHER MOSSY-LOOKING, mat-forming driveway weed is Sagina procumbens, birdseye pearlwort. But unlike the liverwort it is actually a higher (vascular) plant, a relative of carnations in the pinks family or Caryophyllaceae (and also to the more showy Irish moss, Sagina subulata, that we sometimes grow as an ornamental). Also unlike the liverwort, it therefore has a root system, and flowers.

Though various maps of its native range differ, it is certainly native to a wide area, especially in the Northern Hemisphere. It likes cool, moist spots, and even inhabits lawns sometimes (but not mine).

It’s another plant that likes nursery environments, where irrigation is regular, or the shady spots in my driveway that stay moist from poor drainage. Though I could use an herbicide to attack birdseye pearlwort, because it has a vascular system to take up the poison, I don’t use chemicals; I pull it (or use a push-pull Dutch hoe to dislodge it, then rake off the debris). Right now I am frantically doing so in a couple of spots because it is starting to flower—which means more seeds and more Sagina if I let that happen.

If I think Sagina procumbens is an issue here, here’s some chilling perspective: The remote volcanic Gough Island in the middle of the South Atlantic, a World Heritage Site, is home to many birds including the Tristan albatross (above, photo by Michael Clarke from Wikimedia) and Gough bunting, both listed as critically endangered. Sagina has been accidentally introduced there—presumably perhaps from seed on someone’s shoes—and is rapidly damaging the environment. An arduous restoration process is under way (and one is about to kick off to try to eliminate an introduced mouse species that is making havoc, too).

Until I started pulling Sagina in the driveway, and then wondering more about it, I didn’t even know that island or those birds existed. And I didn’t know that liverworts had such an ancient and impressive lineage.

See what your weeds can teach you?

more weedy advice

 

CategoriesNature weeds
  1. I don’t know if I would consider that liverwort a weed. I love seeing them in the wild growing on rock walls etc. I have never seen them in a nursery pot around here. I usually see moss, purslane something along those lines.
    Now the other weed I would agree on. It isn’t even pretty. I hope you win the battle there.

  2. The photo of the liverwort is the same species as the video — Marchantia polymorpha. This liverwort has its own distinctive spore structures that look like little palm trees or umbrellas. The spores are encased in yellow pouches in the upright reproductive structures. Another reproductive structure or botanical feature is evident in your photo as well — gemmae cups that look like tiny teacups. They contain small propagule balls that bounce out in the rain. Liverworts (and other bryophytes) reproduce via spores, propagule balls and any portion of the actual plants themselves, too.

    Marchantia is indeed a common liverwort found in many nursery plant pots. It is resistant to most efforts to kill it. I’ve watched nurseries use powerful chemical killers in efforts to control it but it always seems to come back. Most of my liverwort rescues are from nurseries that don’t want them.

    As a moss gardener, I have included certain liverworts in my experimentation with best species for visual appeal and aggressive growth. The Marchantia can certainly win a prize for aggressive growth patterns. As for visual appeal, the spore structures as unique and fascinating in warm summer months or warmer climates than the mountains of western North Carolina where I live. However, unlike many species of bryophytes, Marchantia doesn’t handle cold weather as well. It will live through freezing temperatures but it turns a slimy. black while my mosses (and other liverwort species such as Bazzania trilobata — not rubbery either like Marchantia) maintain their green appeal throughout the winter season. I found the Marchantia too aggressive in my moss garden and I did not end up liking its winter appearance at all. Thankfully, my Atrichum undulatum (moss) has proven to more aggressive than the Marchantia which is now on the decline.

    As for the Sagina procumbrens, it is THE WEED that plagues my moss garden and gets on my nerves. Upon seeing any of this obnoxious weed with delicate roots that infiltrate my mosses, I pull out every single plant part. It is kind of a “moss faker” in terms of looks and it sometimes it can be confused by the untrained “moss eye” as a moss species. It is not a bryophyte. Although its commercially-sold counterpart is called by the common names “Irish” moss or “Scotch” moss, neither of these vascular plants are true mosses or bryophytes as you’ve pointed out.

    Beauty may be in the eye of the beholder but aggressive, weedy plants (even liverworts) that detract from my mosses are not welcome anymore in my moss garden. — Mossin’ Annie, author, The Magical World of Moss Gardening

    1. margaret says:

      Hi, Annie. I thought so re: the ID of that liverwort, but with things like Bryophytes I never guess b/c I am far from an expert! :) So nice of you to stop in and give us this advanced lesson. The little teacups are adorable, once you get down there and really look at the thing. I do hate the Sagina, too, because it just gets into every crack and crevice here, and as soon as I think I have gotten it … well, you know: there is is in another spot.

  3. Cynthia Donahey says:

    There is this stone bridge under Sunbury Road by Ohio Dominican in Columbus, Ohio allegedly built by Medici engineers. I clambered to the stream bed and looked closer. There was extensive burning and spraying there about fifty sixty years ago, this was one of the plant survivors. The mostly dry stream bed flows sometimes into The Alum. beautiful bridge.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.