If you are like me, you have no idea what a complex thallose liverwort is (like today’s Preissia quadrata!). Thankfully, there are many sources available to us as we embark on a crash-course on liverwort morphology.
Liverworts are possibly the most early-evolved group of plants colonizing land environments. They are non-vascular and spore-producing, so do not have flowers. The UBC bryology course website provides a helpful introduction to liverworts, and explains that there are two types: the leafy liverworts (which look leafy), and the thallose liverworts (which look like flat green pancakes). The thallose liverworts do not have stems or leaves; they have a thallus, which is the undifferentiated vegetative tissue that forms the entire body of the liverwort. Of the thallose liverworts, these are divided into simple and complex groupings. The Friends of the Australian National Botanic Gardens have published an information page about thallose liverworts, which explains that complex thallose liverworts have a thallus that is “many cells thick and the cells in different layers within the thallus have different functions”. The simple thallose liverworts, on the other hand, have a thallus that lacks such differentiation.
Preissia quadrata has flat, branched, leathery thalli (the plural of thallus) up to 1 cm wide. It is found growing in mats in the cracks of alkaline rocks in the Arctic, Subarctic, and high altitude environments in the Northern Hemisphere. The upper surface of the Preissia quadrata thallus is dark green and covered by conspicuous raised air pores. I could write an entire entry about the reproduction of Preissia quadrata, but today I encourage anyone interested in the subject to read this article on liverwort reproductive structures, published by Field Bryology. In the write-up accompanying Robert Klips posting on Flickr, he points out that the specimen photographed was:
beginning to release spores. The black sporophytes are produced on the undersides of the umbrella-like archegoniophore. They look fuzzy because of thread-like twisted elaters which help push out the spores