Although there are many different species of algae, mosses and liverworts, only a relatively few are nursery pests. Chlorococcum humicola Chlamydomonas spp. Unfortunately, nurseries are the perfect home for cryptogams because we encourage them with plenty of water and mineral nutrients. Cryptogams can be a annoyance in bareroot nurseries but they are a serious problem in containers, especially with multi-year crops. Cryptogams are resilient pests because, although they need high moisture levels to grow and reproduce, they can also tolerate long dry periods.
Cryptogams have both direct and indirect effects on seedling growth.
First of all, they limit water infiltration into the soil or growing medium and intercept water and nutrients meant for the seedling crop. Because of their relatively fast growth rates, mosses and liverworts can quickly overtop and smother small, slow-growing seedlings, such as Abies spp. And, although it has not been definitely proven, pathologists suspect that some algae may even produce allelopathic chemicals which inhibit seedling growth. Algae, mosses and liverworts typically enter the nursery as spores but also can be introduced through vegetative means. For example, the liverwort Marchantia polymorpha produces gemmae which are small budlike structures that detach from the parent plant and serve as vegetative propagules.