Liverworts do not have the typical propagules associated with other common weeds. They don't have seeds or asexual propagules such as rhizomes and stolons that can spread and establish as new plants. However, growers wonder how liverworts can become so widely established in the nursery or greenhouse.  

Liverworts can spread and propagate themselves with tiny sexually-produced  spores and asexual propagules.  The flat green leaf-like body of the liverwort spreads horizontally across the media surface by dividing into two branches at apical notches. Each apical notch contains a meristem (here circled in white), basically a growing-point, that can carry on growth laterally if there is media to grow on. Growing-point fragments that are dislodged or torn away from the mother plant have the potential to start new plants. Rhizoids, similar to root hairs, can establish new connections to the media to absorb water and mineral nutrients. 

 

 

 

Probably the most important asexual spread in nurseries and greenhouses is a result of gemmae.  On the upper surface of the liverwort there are 3 to 4 mm cup-like structures called gemma cups, and at the bottom of each gemma cup over a hundred tiny, disk-shaped gemmae can be produced. When water droplets from rain, sprinkler, or an irrigation wand hits the gemma cups, the gemmae are propelled out and can develop into separate plants. Each gemmae produces a clone of its mother plant.

 

Liverworts also spread through sexual reproduction. Each individual plant is either male or female. Male plants make reproductive structures topped by a flattened, lobed disc that produce sperm. Female plants make umbrella-like reproductive structures that produce eggs. In the presence of water, swimming sperm from the male plant can be splashed up on a nearby female structure. The fertilized ovum develops and remains attached under the lobes of the female structure. Male and female spores are produced on hair-like structures that move to facilitate spore release and dispersal.

 

When spores are released they can be spread by air currents. Each female structure produces spores by the thousands. They are very small (less than 3.5 microns in diameter when dry), on the smaller side of most aerially dispersed fungal spores and pollen (which range from 3 to 100 microns). See for yourself in this video below. I recorded in a calm, darkened office. (Be patient for about 20 seconds). When I opened the office door and the fresh air came in, whoosh, away flew the spores.  In the office, not a big deal; when it happens in your nursery or greenhouse, it is a big deal.  These spores might move significant distances even with the slightest of air movement!

 

Next week: what happens after the spores land in your nursery or greenhouse, and management options.

Spore Release video.  Use full screen mode.