This name is a synonym of Archibaccharis serratifolia (Kunth) S.F.Blake.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 2704764) with original publication details: Nov. Gen. Sp. (folio ed.) 4: 47 1820.
This name record (from Tropicos) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Baccharis micrantha in version 1 of The Plant List.