Recognition of Gymnosphaera (Cyatheaceae) as a distinct genus [PASSED]

[dongshiyong]

Author(s) of proposal

Shi-Yong Dong

Name of taxon

Gymnosphaera

Rank of taxon

Genus

Approximate number of species affected

46

Description of change

Gymnosphaera was originally established as a genus by Blume (1828) to accommodate two tree ferns from Java, Indonesia with naked sori and globular receptacles. It was emended by Copeland (1947) to contain tree ferns characterized by dark axes and exindusiate sori which were dorsal on simple veinlets. Holttum (1963) argued to adopt only one genus, Cyathea Smith, to contain all Malaysian species and proposed a subdivision of Cyathea into two subgenera, with each containing two sections. Gymnosphaera was treated as a section under C. subgen. Cyathea and was circumscribed as “stipe-scales flabelloid, sori indusiate, axes very dark, and fertile and sterile pinnules usually very dimorphous” (Holttum 1963). In modern classifications of Cyatheaceae, Gymnosphaera was considered as either a separate genus (e.g., Smith et al. 2006) or a synonym of Alsophila R.Br. (e.g., PPG I 2016). Molecular data, however, strongly supported Gymnosphaera to be a distinct group from Alsophila (Korall et al. 2007, Korall & Pryer 2014, Dong & Zuo 2018, Dong et al., 2019, Loiseau et al. 2020). Based on the remarkable divergence from Alsophila in molecular phylogeny, morphology, and sporogenetic mechanism, Dong and Zuo (2018) reinstated Gymnosphaera was as a distinct genus. There are about 46 species known in the genus Gymnosphaera across the Pantropics (Hassler 2004–2023).

Reason for change

1) Molecular phylogeny: Gymnosphaera was strongly supported to be one of four monophyletic clades (parallel to Alsophila) within Cyatheaceae by the analyses of various combinations of cpDNA sequences (Korall et al. 2007, Korall & Pryer 2014, Dong & Zuo 2018, Loiseau et al. 2020), 12 nuclear single-copy loci (Dong et al., 2019), and the cpDNA genome (unpublished). 2) Morphologe: castaneous or blackish axes and exindusiate sori (Gymnosphaera) versus generally stramineous to brown axes and indusiate sori (Alsophila). 3) Sporogenetic mechanism: 64 spores (Gymnosphaera) versus 16 spores (Alsophila) per sporangium.

Reference(s) for publication of the name

2024 Proposal to recognition of Gymnosphaera as a distinct genus.pdf

List the numbers of any related issues

No response

Code of Conduct

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[SchneiderHarald]

The previous treatment of Gymnosphaera as a synonym of Alsophila reflected uncertainties about the circumscription of the two lineages. These issues have been successfully addressed in the recent years. As a consequence, both the phylogenetic distinction and the circumscription of Alsophila and Gymnosphaera are now unambiguous.

[leonperrie]

Hello Shi-Yong Dong,

Is this a parallel case to issue #73? That proposed segregating Physematium from a monophyletic Woodsia.

Here, Alsophila as circumscribed by PPG 1 is monophyletic.

If PPG wants “to preserve existing taxa and circumscriptions” (PPG I, p. 565) as much as possible, why make a change?

More generally, if a monophyletic group is split into multiple monophyletic sub-groups (or multiple monophyletic groups are lumped), when does taxonomic revision ever end?

Issue #73 did not carry.

[joelnitta]

This proposal was voted on during PPG Ballot 11 (voting period June 2024). A total of 77 votes were cast. There were 67 'Yes' votes (87%) and 10 'No' votes (13%). The proposal passes.