Hothouse is a tour of several biological concepts, ranging from very simple to very complex.

Monoculture

In Hothouse, there is a single, giant banyan tree covering the entire land surface of the earth. By expanding and spreading, it has destroyed all other. Monocultures arise when a single species succeeds in destroying all competitors.

This is an example of the process of competitive exclusion, where one species drives out its competitors. The result is a monoculture, or in this case, a single organism.

Such ecological systems, while stable, are also very brittle and susceptible to attack. For example, if a banyan eating fungus were to evolve, or a banyan-killing beetle, the forest would be utterly destroyed. Without the genetic diversity given my multiple organisms and multiple species, the system is vulmerable.

At the time that events in Hothouse take place, the banyan tree is all-powerful.

Evolution

Aldiss’ fertile imagination generates countless demonstrations of evolutionary processes at work, but the most powerful is the concept of evolutionary forces applied to humans themselves.

Whereas people like to think of the human race as at the top of the food chain and the conquerer of nature, Aldiss has us, mischievously—and plausibly—as small creaturs at the mercy of plants.

Symbiosis

A parasite is a creature that lives off another creature. Examples would be fleas, fungal infections, and viruses. A symbiosis is a relationshp between two creatures or two species that work together for mutual benefit. Examples would be flowers and bees: the bee pollinates the flower, and the flower in turn provides food to the bee.

The partner is a symbiot.

These examples are clear-cut, but the line between symbiot and parasite is often much more blurry, and this line is explored throughout Hothouse. I will describe three examples from the book, but there are many more.

Gren encounters several instances of symbiotic relationships throughout his quest. Some of these at first appear to be parasitic. For example, the pathetic and pitiful tummy-belly men, enslaved by a tree that has its tentacles literally entwined through their bodies. Gren is appalled at their condition, and sets them free.

Once they are free, they are useless, cannot care for themselves, and are generally miserable. Only then does it become apparent that their enslavement also brought them protection, nutrition, and life.

Another symbiotic relationship manifests itself in the prophet Sodal-Ye. This fish-like creature is little more than a talking brain, traversing the planet preaching that the end of the world is coming. Sodal Ye is carried on the shoulder of a person. Without his partner, Sodal Ye would be unable to move anywhere. Together, they are a powerful force.

The symbiotic relationship that drives the narrative is, of course, the relationship between Gren and the Morel. The Morel supplies knowledge amd insight to Gren, while Gren provides the means of using that knowledge. As the story progresses, the view of the Morel shifts from symbiotic partner to parasite.