So, at some point a few hundred million years ago plants figured out how to start growing on land rather than in water. However, at this point in plant evolution, plants reproduced from spores and as such needed to be in an environment with lots of moisture to be able to grow and reproduce. Some plants such as ferns still reproduce in this way and this website has an excellent explanation of how it works. It wasn’t until the gymnosperms came along that plants actually reproduced from seeds. This allowed them to be more successful than the spore reproducing plants at growing in a wide range of climates and conditions. It also allowed the development of the flowering and fruiting plants we know and grow today.
In this article I am going to look at the first ancient plants that evolved from spore reproduction to the first seed bearing plants – the gymnosperms.
What are Gymnosperms
Gymnosperms came about before flowering and fruiting plants (also known as angiosperms) evolved. The term gymnosperm literally means ‘naked seed’, and unlike angiosperms the seeds have no outer shell and are not enclosed in an ovary. The seeds grow in a cone, also called a strobilus. As they don’t produce a flower or a fruit they are pollinated by the wind, not by insects or other animals (mostly!).
There are under 1000 species of gymnosperms in the world with the most recognizable being the conifers such as pine, fir, spruce, and cypress. Gymnosperms are classified into four divisions;
- Coniferophyta, which comprises of around 600 species of conifers.
- Ginkgophyta, the single member being Ginkgo biloba
- Cycdophyta, a group of plants which actually look a lot like palm trees
- Gnetophyta, which consists of 3 genera: Gnetum, which comprises of around 40 species which grow in the moist tropics; Ephedra, which contains around 45 species and is a source of the stimulant and bronchodilator ephedrine; and the super strange looking Weltwitschia mirabilis which is native to the deserts of south west Africa.
Clockwise – Ginkgo biloba leaf, Welwitschia mirabilis, Pine sp., Cycad sp.
The main advantages gymnosperms had over their spore reproducing cousins was that seeds can lay dormant for months or years, waiting for the perfect conditions to germinate and therefore greater ensuring its success in the plant world. The seeds also house the first nourishment the germinating plant needs, giving them a nutritional head start. Animals, such as birds eat the seeds and distribute them over larger distances, spreading the plants genetics into a wider range. As they use pollen instead of spores to reproduce they were able to move away from water sources and inhabit a more varied environment where the spore reproducing plants couldn’t compete.
How Gymnosperms developed
Gymnosperms likely developed from a classification of now extinct plants called progymnosperms. They were possibly the first woody trees and vines on earth. These plants reproduced with spores but produced two, a male and a female, not just one. The male spore being the microspore and the female being the megaspore. These plants, like gymnosperms, are called heterosporous. This set the stage for development of the seed and the evolution of gymnosperms and angiosperms that inhabit the earth today.
How do gymnosperms reproduce?
To demonstrate how gymnosperms reproduce using wind dispersed pollination, here is Pine sp. as an example in this infographic.
References
https://plantfacts.osu.edu/resources/hcs300/gymno.htm
https://www.diffen.com/difference/Angiosperms_vs_Gymnosperms
https://biologywise.com/angiosperms-gymnosperms
https://www.shmoop.com/plant-evolution-diversity/gymnosperms.html
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