Liquid water is a precious resource for most of the life on earth. In areas of scarce natural water, organisms have evolved behaviors and tools that conserve their stores.
Some desert insects, for example, rely on a waxy outer coating to keep from losing excess moisture to the heat of the sun. Due to their specific compositions, many of these waxy coatings actually change shape when the organism reaches high temperatures, allowing excess heat to escape for a short time and re-forming once cooled down.
A wide variety of plants known as succulents have also taken on unique modifications in order to help survive hot and dry environments.
While there are a large variety of succulents, cacti are probably some of the most commonly seen and remembered due to their size, spines and interesting shapes.
In general, cacti are flowering plants that realized the traditional shape of thin, wide leaves simply lost too much water through heat, wind and normal photosynthesis to be useful in a dry and hot environment.
The vast majority of cactus species are native to the Americas, with several even able to survive freezing temperatures by distributing antifreeze solutions throughout themselves. In order to combat water loss, ancient cacti shed their leaves and developed complex layers of cells on their stems that photosynthesize instead. In order to allow ample sunlight to reach these cells, early cacti were forced to ditch their protective layer of bark as well.
To protect themselves from the mouths of predators, most cacti began to modify what was left of their leaves into hard and sharp spines. Spines also help collect moisture from morning dew, lightly shade the stem and help buffer the cactus from any harsh winds.
Similar to desert insects, the outer layers of cacti stems are made of waxy layers that help retain water. Their oftentimes cylindrical or spherical shapes help reduce surface area, and are able to grow and shrink depending on the amount of water held inside to further aid in water retention.
During good times, the mass of a cactus can be up to 90 percent water. This water is brought in by a vast network of shallow roots that reach out over wide distances, giving the plant access to as much real estate in the splash zone as possible. Even though most cacti no longer produce leaves, they still produce flowers from the round structures that also grow spines.
Most cacti are pollinated by bees and hummingbirds, however some only open their flowers at night and rely on bats or moths for their pollination. In fact, cacti are still very active after the sun goes down.
Cacti and other succulents utilize a method of photosynthesis that helps them to cut down on daytime water loss. They open microscopic pores called stomata in their outer waxy layers at night in order to capture carbon dioxide from the air, storing it in the form of malic acid.
During the heat of the day, these pores are kept closed, and the plant relies on the malic acid from the previous night for the carbon dioxide used during photosynthesis. Succulents are able to therefore seal themselves off from hot and dry daytime air, which would suck deadly amounts of moisture from them if their stomata remained open throughout the day.
Cacti are popular household plants, however they can easily be killed by the over-attentive waterer. Make sure to place any new or struggling cacti in well drained soil, and only water when the soil has dried out and the plant looks mildly deflated.
Brannen Basham and his wife, Jill Jacobs, operate Spriggly’s Beescaping, a business dedicated to the preservation of pollinators. He can be reached at firstname.lastname@example.org.