Round Shape Reduces Water Loss

Biological Strategy

Pebble plants

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Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The rounded shape of the leaves of pebble plants minimizes evaporation due to its low surface area relative to volume.

“Pebble plants grow in the stonier patches of the same [Namib] [D]esert. They survive by living partly underground. Their leaves have been reduced to a single pair, fat, round and succulent, with just a groove between them from which, in the right season, will sprout a surprisingly large flower. Such a rounded shape, with a very low surface area for a given volume, reduces evaporation to a minimum and is therefore a great help to the plant in conserving its water in the intense heat. But as has been noted earlier it may bring an additional benefit. Outside the flowering season, the plant is very difficult to find among the gravel and pebbles, so its shape could also serve as a defence against detection by grazing animals — ostriches and tortoises, porcupines and perhaps a few gerbils.” (Attenborough 1995:265)

Last Updated September 14, 2016

References

Book

The Private Life of Plants

BBC Books | 21/08/1995 | David Attenborough

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