Brian Aldiss was one of the "New Wave" of British SF authors in the 1960s, signalling a break from traditional SF themes towards more experimental fiction. Aldiss himself alternated between mainstream and genre fiction and is regarded as a "literary" author, with a high critical reputation. Hothouse (initially published in the USA in abridged form as The Long Afternoon of Earth) is an early and more conventional work, fitting within the SFF mainstream. Despite being described as SF, this story is more of a fantasy in my view, as I will explain.
The setting is the very far future, close to the end of the Sun's life, when Earth has settled into an orbit which keeps one side turned permanently to the Sun, and the Moon has become a twin planet, also remaining in the same place relative to the Earth and now supporting life. The habitable part of the Earth is entirely covered by one vast, interconnected banyan tree, and inhabited by various (and usually ferocious) vegetables and insects. Humans - in a considerably shrunken form - are almost the only animals left, and exist in small groups at pre-stone age survival level in the middle layers of the forest, constantly threatened by predators.
I should warn you that the rest of this review contains spoilers, as it's difficult to comment on the story without them, so I will just sum this up as an interesting period piece, highly regarded when it first appeared, but not standing up too well today.
The protagonist is Gren, a rebellious near-mature male child in a society run by women. He and the other children are abandoned by the adults of their group who head off into the sky in a strange ritual, eventually arriving (much changed) on the Moon.
Gren and the other children are almost immediately in one set of trouble after another, and Gren's disruptive behaviour eventually causes him to be exiled. He falls prey to a morel, an intelligent fungus which invades and takes over his nervous system and is able to ransack his race memories to learn the history of humanity. With the morel's somewhat unreliable guidance Gren is able to survive, meeting various people and weird life forms and experiencing one adventure after another. He meets Sodal Ye, an intelligent dolphin who is aware of the history of the world and of its imminent destruction as the Sun goes nova. Finally, the transformed adults of Gren's group return from the Moon, and Gren is faced with a choice of futures.
I said at the start that I regarded this story as a fantasy despite an attempt by the author to establish it as set in a possible future. This is because some of the aspects of it - especially the space-travelling traversers and the bizarre tummy-belly men - are just too fantastic to be credible, at least as far as I'm concerned. Which does, of course, open the door to the age-old debate about where the boundaries between the two genres lie, but I'll save that for another time.
I enjoyed this re-read rather less than I expected. Partly this is because the principal character is so unsympathetic - the kind of brash and self-centred youth I would dislike in real life - partly because the procession of one fantastic creature after another becomes a bit wearing. The story reads as if the author was packing in as many bizarre ideas as he could, just for the sake of it.
I was also not entirely comfortable with one aspect of the writing; the narrator, who kept throwing in additional pieces of information to explain the background. Some of it made no sense: for example, the entertainingly-named killerwillow, bellyelm and sand octopus, which only lived in Nomansland where no human ever went - so how did they acquire such names, if no-one knew they existed?
A few more general comments:
There are various possible ways of making the reader understand unusual settings. One (popular these days) is to explain nothing, leaving the reader to piece together what the story is all about from scraps of information scattered through it, and possibly even remain a bit puzzled at the end. A second is to build in occasional infodumps in the form of the notorious "As you know, Bob" type of conversations; however, this isn't possible in a story like Hothouse, in which none of the characters understands the background until the morel and Sodal Ye appear. Another might be for the characters to stumble upon some ancient document which explains it all (also not applicable to Hothouse, where no-one can read). Or there could be a prologue which gives a summary of the back-history, but that could spoil the surprise element. A further approach is explicitly to establish the narrator as being in the future, looking back and describing what happened; a variation on this is to supplement the narrator's role with extracts from a history written in some future time, inserted before the start of each chapter (a technique used effectively by Frank Herbert in Dune); but again, neither is applicable to Hothouse, where there is no prospect of any future historian.
As a general rule I prefer the narrator to be unobtrusive, simply describing what is happening and what the main viewpoint character is thinking. Aldiss' approach left me uncertain about who the narrator was meant to be; seemingly, some all-knowing commentator rather than an observer of current events. On balance, I would have preferred a brief prologue for this novel, probably only a paragraph, explaining about the changes in the orbital behaviour of the Earth and the Moon and their consequences for life, because these are explained by the narrator early on anyway. The rest of the explanations could have been handled by the morel and Sodal Ye.