Ageratum littorale, the Cape Sable whiteweed, is a plant species native to Florida, the common name referring to Cape Sable inside Everglades National Park.

Some publications (e. g. Flora of North America)[3] consider this as being the same species as the West Indian A. maritimum, but The Plant List[1] accepts the two as distinct taxa.

Ageratum littorale grows in beach sand and nearby thickets along the coast as well as hummocks and roadsides at elevations of less than 10 m (33 ft).

It is a trailing to decumbent perennial herb up to 50 cm (19.5 in) tall, spreading by means of underground rhizomes.

Flowers are blue, lavender or white, in cyme-like arrays.