From pre-historic Charophytes to Angiosperms.A crash course in the evolution of terrestrial plants.

The end of the Mesozoic era 140 million years ago not only led to the mass extinction of dinosaurs, the once dominant gymnosperms which covered the earths landscape would also diminish. Perhaps the most important evolutionary event within the kingdom Plantae at the time, was the evolution of seeded flowering plants, angiosperms (Rost 1998). Angiosperms are all grouped within the phylum, Anthophyta. Angiosperms, meaning “seed within a vessel”, make up 90% of all plants we see today, between 300-450 000 species, making them by far the largest phylum of photosynthetic organisms (Evert and Eichhorn 2013). Much like gymnosperms, angiosperms also produce seeds, however, many characteristics of their life cycles differ greatly. The ovaries of angiosperms are enclosed within the carpel and ovules have two layers of protective integument, whereas gymnosperms have a single integument (Rost 1998). Comparison of gymnosperm and angiosperm integument layers Angiosp

There are several phyla which became extinct towards the end of the Mesozoic era 65 million years ago, such as the Pteridospermales and Cordaitales, however, this blog will focus on the 4 extant phyla, Coniferophyta (conifers), Cycadophyta (cycads), Ginkgophyta (ginkgo) and Gnetophyta (gnetophytes) (Evert and Eichhorn 2013). The most abundant of all gymnosperms, with approximately 630 species, are the conifers, Coniferophyta (Evert and Eichhorn 2013). These include some of the more commonly known like red woods, pines, firs and cypresses, and others less familiar such as larches, bristlecones, junipers, yews and plum yews (Rost 1998). Not all conifers are cone bearers as the phylum name suggests. Junipers, yews and plum yews are unique in that they lack woody cones.  Giant Sequoia pinecones They have seeds which are surrounded by a fleshy, berry like tissue, called an aril, and are fruit like in appearance (Rost 1998). There are other unique features within the conif

Throughout the Permian period, which marked the conclusion of the Paleozoic era and the commencement of the Mesozoic era, the earth’s climate changed from warm, moist and humid, to cooler and much drier (Rost 1998). During this period, known as the dinosaur era, the dominance of seedless vascular plants throughout the prehistoric landscape came to an end.  Artist impression of Gymnosperms and dinosaurs during the Mesozoic era Seeded vascular plants are true terrestrial plants (Willis & Mcelwain 2014). With unique life cycles, which allow them to thrive in much drier climatic conditions, seeded vascular plants are much less reliant on free water than seedless vascular plants. Much like amphibians, seedless vascular plants relied on wet and moist conditions for the success of their reproductive cycles (Rost 1998). The evolution of the ovule, the seed, and pollination, allowed for the successful radiation of gymnosperms throughout the Mesozoic era and into our current pe

The marshy forests of the Carboniferous period, 295 million years ago, were not only filled with tall, Lycophytes, they were also abundant with Pterophytes, such as ferns, and horsetails (Reece & Campbell 2012). Within this phylum, and perhaps the most familiar to us, is the fern, Filicopsida . Artist impression of Carboniferous forest. Today there are approximately 12,000 extant species of ferns distributed worldwide, that make up the largest, most diverse group of all vascular plants (Pearson 1995). Most species of fern favour moist, shaded tropical climates, are herbaceous, and have large macrophylls called fronds. Fern sporophyte extend themselves through the tip of an underground perennial stem, called a rhizome (Rost 1998). From this horizontally branched dichotomous stem, adventitious roots radiate underground, whilst fronds arise vertically from the rhizome. Young fern fronds are coiled tightly and aptly named fiddleheads, as they resemble the head stock

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

The evolution of seedless vascular plants towards the end of the Silurian period, 425 million years ago, allowed for the re-transformation of the pre-historic landscape. Originally desolate, then gradually filled with vertically challenged, ground hugging bryophytes; The rise and prominence of seedless vascular plants allowed for rigidity & vertical growth, which had previously eluded the first permanent land dwelling flora (Evert, Raven & Eichhorn 2013).   As we’ve learnt from previous posts, both charophytes and bryophytes lacked vascular tissue. This inevitably restricted their ability to grow vertically, but also radiate in their new found terrestrial environment without the constant availability of surface or ground water (Willis & McElwain 2014). So, what enabled seedless vascular plants to rise above their non-vascular counterparts, and successfully dominant the Silurian-Carboniferous landscape? One of the most significant evolutionary innovations, along wit