Field of Science

Plants rule!

What can you say? When it comes to –estiness, plants rule! Let’s see the score card: biggest living organism (in mass) - Pando aspen clone, fully connected at about 6,000 tons (biggest in size would be a fungus), oldest single living organism (not counting clones, if allowed it would be Pando again at maybe 80,000 years) – Norway spruce at about 10,000 years, oldest living genus – Selaginella (alive in the Carboniferous), oldest living species at 70 million years – Cinnamon fern, largest chromosome number – adder’s tongue fern at 2n = 1260, largest sperm – a cycad sperm cell is visible to the naked eye, if you know where to look. Zowie! There hardly seem to be any –est categories left, but here’s another, the largest genome.
Paris japonica, a relative of Trillium that can't count (probably should have been named Quadrillium), has over 150 billion base pairs in its genome in comparison, humans have about 3 billion base pairs, so the genome of this little woodland wild flower is 50 times bigger than ours. In case you’ve forgotten your freshman biology, genes are composes of a sequence of 4 nucleotide bases, adenine, thymine, guanine, and cytosine, and taken three bases at a time they spell out the genetic coding for each of the 20 amino acids that compose our proteins. It isn’t clear how or why an organism should have such a large genome, although hybridization and chromosome doubling is a common mechanism of speciation among plants, but even with over 1200 chromosomes, the adder’s tongue fern doesn’t have a genome any where near that huge. However, organisms with big genomes seem to be at greater risk of extinction, again for uncertain reasons; perhaps they may be unable to deal with changing conditions because they have so many copies of each gene, which would be like tossing a thousand coins versus two coins. In the latter case they come up HH or TT 25% of the time, but with a large number of coins the ratio of H:T will always be close to 50:50 and never even close to all heads or tails.

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