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
- How to ID your weeds
- Why weeds succeed
- A 101 approach to weed control
- Smothering weeds with cardboard and newspaper
- Piling on the mulch for weed suppression and control
- Poison ivy 101
- Spotted spurge and hedge bindweed
- Clearweed, or Pilea pumila
- Garlic mustard, Alliaria petiolata
- Galinsoga and Commelina
- A weed I accidentally planted, Houttuynia or chameleon plant
- All my weed stories