Desmarestia tropica, sometimes called tropical acidweed, is a species of seaweed in the family Desmarestiaceae.

[1] Endemic to the Galápagos Islands,[1] the specific epithet tropica alludes to its tropical habitat, rare for members of Desmarestiales.

[1] This event killed much of the macroalgae in the area,[1] and D. tropica likely declined from overgrazing by herbivores resulting from El Niño and overfishing of predator fish.

[5] D. tropica is in the section Herbacea of Desmarestia, but compared to other North American species it is less membranous.

[4][1] Despite its tropical range, it prefers the cold, deep water[1] of upwelling areas of the lower sublittoral zone.