This name is a synonym of Cyathea decrescens var. quadrata (Baker) Janssen & Rakotondr..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 26600545) with original publication details: Bull. Soc. Bot. France 88: 681 1941.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:17382950-1.
This name was in version 1 of The Plant List, record tro-26600545, and has not been changed.