Byron and Phyton, Meet the Bryophytes!

During the Upper Ordovician era 475 million years ago, the terrestrialization of charophycean algae led to the evolution of the first permanent land-dwelling plants, the bryophytes (Willis & McElwain 2014). The term bryophyte is derived from the Greek words Byron, meaning moss, and Phyton, meaning plant (Reece & Campbell 2012). It is used to describe plants with no vascular or specialised transportation system. There are three phyla within the bryophyte group. Anthocerophyta, the hornworts. Bryophyta, which are the mosses. And lastly, Hepatophyta or the liverworts (Reece & Campbell 2012).

(Classification of bryophytes, Plant science 4 U 2016)

Although bryophytes lack a specialised vascular system, they do have simple water conducting cells which are non-lignified (Willis & McElwain 2014). They also have several shared characteristics with vascular plants of today, which enables them to be distinguished from charophytes (Evert, Raven & Eichhorn 2013). These characteristics include tissues produced by an apical meristem, protectively walled gametangia, matrotrophic embryos, sporopollenin-walled spores, and life history involving the alternation of heteromorphic generations (Evert, Raven & Eichhorn 2013).

Although both vascular plants and bryophytes have alternation of generations, in which the gametophyte differs from the sporophyte, there are major differences within the life cycle of bryophytes. Due to free living gametophytes, and a sporophyte which is permanently attached to its parental gametophyte, emphasis is placed on the gamete-producing generation (Evert, Raven & Eichhorn 2013). During the sporophyte generation spores are also produced which allow for maximum distribution through anemochory (Willis & McElwain 2014).

Bryophytes also lack true stems, leaves and roots and are mostly small herbaceous plants. With the absence of vascular tissue in bryophytes, vertical growth was restricted. To overcome this, bryophytes adopted dorsiventral shaped growth. This is where the plant does not grow vertically, only horizontally across the substrate in which it is anchored to via rhizoids (Willis & McElwain 2014). This allows for greater surface area across the entire plant to absorb sunlight for photosynthesis, and,water absorption from condensation or moisture directly across the cell surface (Evert, Raven & Eichhorn 2013).

The bryophytes are a vital piece of the plant puzzle, which allows us to understand the origin and transition of land plants and their importance in many ecosystems today.

References

Evert, R.F., Raven, P.H. & Eichhorn, S.E. 2013, Biology of plants, Eighth edn, W.H. Freeman and Company Publishers, New York.

Pearson, L.C. 1995, The diversity and evolution of plants, CRC Press, Boca Raton.

Reece, J.B. & Campbell, N.A. 2012, Campbell biology, 9th (Australian version) edn, Pearson Australia, Frenchs Forest, N.S.W.

Willis, K.J. & McElwain, J.C. 2014, The evolution of plants, Second edn, Oxford University Press, Oxford.

Plant science 4 U 2016, The classification of bryophytes, image, viewed March 2018, <https://www.plantscience4u.com/2014/04/classification-of-bryophytes.html#.WrXjUnpuaHs>.

Dr Larry Jensen 2003, Reproductive cycle of mosses/ The amazing lives of plants. [online video]
Available at: https://www.youtube.com/watch?v=_MFnZjpTFT8 [accessed 24 March 2018]