Seeds spread from the dandelion plant Taraxacum. (Photo credit: Peter Cade via Getty Images)
Seeds have enabled plants to evolve into the amazing variety of forms that fill our planet with color and provide us with food and medicine. It is difficult to imagine how plants would have evolved without seeds. The question is, where did the first seeds come from?
Plants began using seeds to reproduce in the late Devonian period (419 to 359 million years ago). Scientists continue to investigate the exact evolutionary origins of seeds, but the earliest known fossils of seed plants date back to the Famennian period, which began about 372 million years ago.
For example, Famennian fossils of the plant Elkinsia polymorpha found in West Virginia show seed shoots, according to the University of California, Berkeley Museum of Paleontology. Researchers have also found other examples of ancient seeds in Europe and China.
Plant biochemistry professor Gerhard Leibner, who leads the seed research group at Royal Holloway, University of London, believes that plants probably evolved seeds soon after they began living on land.
“They came out of the sea about 450 million years ago,” Leibner told Live Science. “A little bit later, there was an era when ferns ruled the world, and they had spores, and from those spores, it's thought, the seeds of plants evolved.”
Some plants, such as mosses, algae and ferns, continue to use spores to reproduce instead of seeds, according to a 2019 article in The Conversation by Marjorie Lundgren, a senior research fellow in plant environmental physiology at Lancaster University in the UK.
A spore consists of a single cell with DNA from a single parent plant, while a seed is a more complex multicellular organism that usually requires two parents. A spore with a single parent must first develop into a pre-plant stage known as a gametophyte, and only becomes a plant after two gametophytes combine to undergo fertilization. Seeds, on the other hand, skip this stage, as the female plant produces seeds from the pollen of the male plant after fertilization.
Leibner noted that seeds have many advantages over spores. They can be much larger and have a tough protective shell, making them more resilient. They can also store nutrients to provide the new plant with an immediate source of energy.
Horse chestnut is the fallen seed of the horse chestnut tree (Aesculus hippocastanum).
Spores also tend to require a lot of moisture to avoid drying out, while seeds are able to adapt
Sourse: www.livescience.com
