If James M. Cain wrote history, this is the style he would employ.
Hobhouse's terse, unflowered prose moves the narrative along, and he
has an an attitude: cynical. If you liked Marvin Harris and Jared
Diamond, and I know you did, you'll like Henry Hobhouse because he has
a similar myth-exploding, cant-debasing, and finely tuned BS detector
a-working.
The five plants are quinine, the potato, sugar cane,
cotton, and tea. He's a little thin on the properties of the plants,
but strong on the historical consequences. His explanation of why
slavery died and why it remains a dead institution is excellent. (NOT
because it is immoral, although it is that, but because slavery is
inefficient, economically speaking.) Beware some unusual syntax.