[2] The leaves have three leaflets which are bent back in the bud and are later held in a horizontal or deflexed position.

In H. microphylla, in contrast to other members of the genus, this capsule has thin, leathery valves and does not burst open when ripe to expel the seeds.

[2] H. microphylla is an uncommon species endemic to the upper and middle reaches of the Rio Negro, a left-bank tributary of the Amazon River.

It mostly grows on river banks or islands and the sandy or laterite soils it favours are heavily inundated by flood water for at least four months each year.

[2] H. microphylla is not exploited in the wild, probably because of the poor quality of the latex which is mixed with resins, and it is not cultivated.