Both Cyathea hancockii and Alsophila denticulata were treated as synonyms of Gymnosphaera denticulata by Dong and Zuo (2018) based on the molecular evidence and morphology.

Shi-Yong Dong, Zheng-Yu Zuo (2018) On the Recognition of Gymnosphaera As a Distinct Genus in Cyatheaceae. Annals of the Missouri Botanical Garden, 103(1), 1-23
https://bioone.org/journals/Annals-of-the-Missouri-Botanical-Garden/volume-103/issue-1/2017049/On-the-Recognition-of-Gymnosphaera-As-a-Distinct-Genus-in/10.3417/2017049.short