The Genocides

Alien plants take root on earth, sap the planet of its vital nutrients, decimate modern civilization and the human race. The patriarch of the last band of humans is a religious nut job who whips his grown children. The roots of the plant turn out to be full of spun sugar which is edible in moderation. Seriously. The femme fatale of the group eats too much and turns into jabba the hut. SPOILERS She ends up being too gelatinous to leave their underground root system sanctuary.

This book was like someone took a SyFy made for TV movie but wrote the screenplay in 1960 and had Heironymus Bosch do the storyboards. Somehow I mean that in a begrudgingly good way.