Lifestyles of Lycophytes

From the mid Devonian, to the end of the Carboniferous period, 394 to 294 million years ago, the evolution of the vascular system allowed terrestrial flora to dramatically evolve from relatively small stature to towering spore producing trees, up to 40 m high and 2 m in diameter (Reece Campbell 2012). During this period there were several major evolutionary clades which dominated the landscape, some of which are now extinct. These included the phyla Lignophyte and Pseudosprocnus (Willis McElwain 2014). This post will focus on the first of the two extant phyla, Lycophyta and Pterophyla.

The most ancient of vascular plants are within the phylum Lycophyta. This phylum consists of the quillworts, club mosses, spike mosses.Although named as such, due to size and physical appearance, they are not true mosses, due to the presence of microphylls and dichotomously branched roots (Rost 1998). Presently there are 1200 species within this phylum. They range from tropical climates, where they symbiotically thrive as epiphytes, to more temperate climates, where they cover forest floors (Reece Campbell 2012). In varying species, gametophytes can either be photosynthetic, living above ground, or subterranean, living symbiotically with fungi (Reece Campbell 2012).



All Lycophytes have a sporic life cycle, however, sexual reproduction varies within the phyla. Club mosses, produce bisexual spores within sporangia which are homosporus, a single size, and are clustered together as strobili, positioned on upright stems on the tips of the sporophyte (Rost 1998). 

Club moss lifecycle


In contrast, both spike mosses and quillworts are heterosporous, producing two types and sizes of spores, large megaspores (egg), and smaller micro spores (sperm) (Rost 1998).


Spike moss and quillwort lifecycle


Spike and club mosses tend to stay small in stature, grow horizontally and have small microphylls, whereas quillworts, grow quite vertically and have grass like microphylls, similar in shape to monocotyledonous plants (Pearson 1995). Quillworts are the closest relatives to the large ancient lycophyte trees, which filled swamp like forests during the Carboniferous period (Evert Eichorn 2013). Our coal sources today, were formed from the decaying remnants of these ancient lycophytes, which formed into peat, lignite and ultimately coal through sedimentary processes over the last 290 million years (Willis McElwain 2014).






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.

Rost, T.L. 1998, Plant biology, Wadsworth, Belmont, Calif.

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

Echezabalperiod2 2018, Homosporous lifecycle, image, viewed April 2018, < https://echezabalperiod2.wikispaces.com/Club+Moss>.

Echezabalperiod2 2018, Heterosporous lifecycle, image, viewed April 2018, < https://echezabalperiod2.wikispaces.com/Club+Moss>.

newtechbio2011.wikispaces.com, Lycophyta, image, viewed April 2018 <
https://newtechbio2011.wikispaces.com/Lycophyta>.

 https://www.youtube.com/watch?v=kdDMvWqzHfw
Biotech guru 2014, Life cycle: Selaginella apoda [Online video] Viewed April 2018

Comments

  1. Tasmin7 April 2018 at 22:35

    An interesting group of plants. Which of these would be considered the basal or ancestral group in terms of life cycle? Is homospory ancestral, or heterospory?

    ReplyDelete

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