The diversity of plants

In this post, I wish to discuss the diversity of plant life on planet Earth. Plants are sometimes overlooked in the study of the natural world. However, I hope to convince you that they are as charismatic and enigmatic as any animal or bacterial species.

Flowering plants, also known as angiosperms, are the largest group with an estimated 300,000 to 370,000 species [1]. Angiosperms include everything from potatoes, cotton, rice, bananas and beyond. As the largest group of plants, they are well studied in the fields of botany and evolutionary biology. Pressing questions in botanical research aims to decipher how flowering plants have evolved and the major contributing factors that have led to their diversification. There are also lots of smaller, less well-known groups that have exciting shapes, forms and ecological roles.

Gymnosperms are fascinating plants which bear seeds but do not have flowers. Groups within the gymnosperms include conifers (pines), ginkgos and cycads. These plants were present during the time of the dinosaurs and are long lived species [2]. The oldest pot plant at Kew Gardens, for example, is a cycad, Encephalartos altensteinii, and has been in the collections since 1773.

Repotting the oldest pot plant - Kew
Encephalartos altensteinii – edited from Plants of the World Online

Ferns and lycophytes are two distinct groups of plants that do not have flowers or seeds. Instead they reproduce through shedding spores. Both of these groups have vascular tissue. This is the combined definition for two types of tissue that i. enables the transportation of water and minerals throughout the plant (termed xylem) and ii. conducts the products of photosynthesis (termed phloem). Ferns are distinguished from lycophytes through the development of true leaves, called megaphylls [3].

Finally the last group I wish to mention are the bryophytes which include mosses, liverworts and hornworts. Interestingly, these plants lack flowers, seeds and vascular tissue. They are also fascinating as they are thought to be the closest relatives to the very first land plants. These ancient relatives are believed to have colonised land from aquatic environments approximately 450 million years ago (mya) and led to the development of the planet’s oxygen rich atmosphere [4].

Hopefully, I have begun to introduce the great diversity of plants with multiple shapes, forms and features such as fascinating methods of reproduction. With an estimated 400,000 species, this is an area of plant biology I will be returning in my blog postings. My PhD project aims to utilise this diversity and our current knowledge of these evolutionary relationships to investigate how genes have evolved and developed across the plant tree of life.

If you want to learn more:

  1. Christenhusz, J.M. & Byng, J. W. 2016. The number of known plants species in the world and its annual increase. Phytotaxa. 261 (3): 201–217.
  2. Barrett, L. M. & Willis, K. J. 2001. Did dinosaurs invent flowers? Dinosaur—angiosperm coevolution revisited. Biological Reviews of the Cambridge Philosophical Society. 76 (3): 411–447.
  3. Schneider, H. & Schuettpelz, E. 2016. Systematics and evolution of lycophytes and ferns. Journal of Systematics and Evolution. 54 (6): 561–562.
  4. Lenton, T. M., Dahl, T. W., Daines, S. J.,  Mills, B.J.W., Ozakid, K., Saltzmane, M. R. & Porada, P. 2016. Earliest land plants created modern levels of atmospheric oxygen. PNAS. 113 (35): 9704–9709.

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