wtesto
commented
1 year ago I wish to weigh in on this proposal, as I am one of the folks responsible for the recognition of Zealandia and the resurrection of Dendroconche, both of which would be treated within Lecanopteris if this proposal were accepted.
The non-monophyly of Microsorum and several related genera is well-documented (Kreier et al., 2008; Testo & Sundue, 2014; Chen et al., 2020) and has stymied efforts to produce a satisfactory generic level classification of Polypodiaceae subfamily Microsoroideae. Testo et al. (2019) generated a phylogeny of subfamily Microsoroideae using four chloroplast loci and 167 taxa – including the type species of all 12 genera recognized by PPG1 (2016) for the subfamily – and demonstrated that 16 taxa that had treated as Microsorum and Colysis were not closely related to those genera and instead formed three monophyletic groups that were successively sister to Lecanopteris. Using ancestral character state reconstruction of six morphological characters, Testo et al. (2019) demonstrated that each of the three groups presented readily evident synapomorphies and all of them could be easily distinguished from each other and from Lecanopteris. We recognized these three clades at the generic level – one name (Dendroconche) was resurrected from synonymy, and two others (Bosmania and Zealandia) were newly described.
As thus circumscribed, the four genera of lecanopteroid ferns (tribe Lecanoptereae C.C. Chen & H. Schneider) are:
Lecanopteris, characterized by an association with ants that live in cavities either within or underneath dramatically enlarged rhizomes.
Dendroconche, characterized by hemiepiphytic growth habit, non-pruinose rhizomes, non-impressed sori, bright yellow verrucate spores, and specialized laterally inserted clasping roots used for climbing.
Zealandia, characterized by (mostly) epiphytic growth habit, deeply impressed sori that are readily visible on the adaxial laminar surface, prominent veins that contrast strongly with the laminar tissue, and pruinose rhizomes.
Bosmania, characterized by terrestrial growth habit, membranaceous laminae, and simple leaves that are deciduous in the dry season.
These synapomorphies are supported by ancestral character state reconstructions and images are provided to guide users.
The monophyly of these genera was supported by a subsequent study (Chen et al. 2020) with improved taxon sampling and a different set of loci, though that study recovered Dendroconche (vs. Zealandia in Testo et al. 2019) as sister to Lecanopteris. Chen et al. (2020) compared the generic classification proposed by Testo et al. (2019) to two alternatives involving a more broadly construed Lecanopteris; they concluded that extending Lecanopteris to include Dendroconche was “less suitable” than recognizing the latter as a distinct genus and that recognizing Lecanopteris with Dendroconche and Zealandia included in it “would still perhaps not be the best option because it would be morphologically poorly defined.”
As proposal #28 shows, Perrie et al. (2021) rejected the recognition of Zealandia and Dendroconche in favor of an expanded Lecanopteris that includes those taxa. Here, I will outline the main arguments presented by Perrie et al. (2021) for expanding Lecanopteris and explain why I think recognition of four genera within Tribe Lecanoptereae is preferable.
Utility and stability of genus-level synapomorphies: Perrie et al. (2021) suggests that “the morphological characterisation of an expanded Lecanopteris including the Dendroconche and Zealandia lineages is just as good, if not better, with the pertinent character states being the absence of sclerenchyma strands in the rhizome and at least some of the fronds having Nooteboom’s type 5 venation pattern.”
With the exception of Zealandia powelii, all of the species included in Lecanopteris by Perrie et al. (2021) lack free sclerenchyma strands in the rhizome, though many of these species do possess sclerenchyma bands associated with the rhizome vasculature (Bosman, 1991; Nooteboom, 1997; Testo & Sundue, 2014). In addition, and as pointed out by Perrie et al. (2021), numerous taxa that belong to non-lecanopteroid lineages in subfamily Microsoroideae also lack sclerenchyma strands in the rhizome, including species of Microsorum, Lepidomicrosorium, Neocheiropteris, and several unplaced taxa.
Further, the type 5 venation pattern of Nooteboom (1997) is not present in all species included in Perrie et al.’s concept of Lecanopteris (Zealandia powellii lacks such venation) and is only present in the fertile leaves of what is by far the most commonly collected species in the clade (Zealandia pustulata). They also report that “type 5 patterns were recorded for several species currently unplaced phylogenetically but which may be lecanopteroids.” This includes Microsorum aurantiacum, which was suggested by Nooteboom (1997) to be a close relative of taxa now placed in Zealandia, but which possesses sclerenchyma strands in the rhizome, thereby presenting another potential exception to the characters used by Perrie et al. (2021) to support an expanded Lecanopteris.
The above is Figure 2 from Perrie et al. (2021), which shows (from left to right) venation types 5, 3, and 1 of Nooteboom (1997). In my view, the differences between these venation types are subtle and considerably more challenging to interpret than the characters proposed by Testo et al. (2019) as synapomorphies for the genera recognized therein.
With character stability set aside, I do not agree with Perrie et al.’s claim that “the morphological characterisation of an expanded Lecanopteris including the Dendroconche and Zealandia lineages is just as good, if not better,”than the traditional circumscription of the genus on the basis of myrmecophily and highly modified rhizomes, like these (photo by Chuck Hung, used under CC BY-NC-SA license):
Perrie et al. (2021) also argue that myrmecophily and rhizomes with ant domatia are not suitable synapomorphies for Lecanopteris, as they occur in other genera of Polypodiaceae. They do not, however, apply the same logic to the presence of sclerenchyma strands in the rhizome or reticulate venation with large costal areoles, the characters they use to define the genus. Both characters occur in many genera of Polypodiaceae and other fern families and are doubtlessly much more homoplastic than than ant-fern symbiosis like that found in Lecanopteris.
Setting this point aside, both the classification schemes of Testo et al. (2019) and Perrie et al. (2021) utilize some synapomorphies that are not unambiguous (i.e. those character states are not shared by all members of the genus or they occur in other clades); this is certainly not unique to this group of ferns. In such a case, having a greater number of characters that together define clades –like the classification of Testo et al. (2019)-- is clearly preferable. This approach to classifying the lecanopteroid ferns promotes recognition of genera that are more morphologically cohesive, share a larger number of evident synapomorphies, and maintains the long-standing circumscription of Lecanopteris, one of the most distinctive Polypodiaceae genera.
Stability in the face of phylogenetic uncertainty:
Perrie et al. (2021) argue that an expanded Lecanopteris is better suited than the classification proposed by Testo et al. (2019) to accommodate phylogenetic uncertainty in the microsoroid ferns. This uncertainty is problematic in part, they suggest, because Testo et al. (2019) and Chen et al. (2020) recovered different phylogenetic relationships for the genera in tribe Lecanoptereae, and Perrie et al. (2021) depict the relationships of Dendroconche, Zealandia, and Lecanopteris with a polytomy (Figure 1). Though Testo et al. (2019) and Chen et al. (2020) do differ in the clade they recover as sister to Lecanopteris, neither study recovers a polytomy, and all the genera proposed by Testo et al. (2019) are strongly supported as monophyletic in all analyses conducted by both Testo et al. (2019) and Chen et al. (2020).
Following up on this, Perrie et al. (2021) point to numerous species currently treated in Microsorum that have not been placed in a phylogenetic context and may eventually be found to be members of tribe Lecanoptereae. They state that “if any of the unplaced species did not fall within the already identified lineages (as happened within this geographic region for some New Caledonian Lastreopsis; Gardner et al. 2017), then additional genera would be required.*** While that could happen at some point in the future, I do not agree that such a possibility is “arguably a significant problem,” as Perrie et al. (2021) posit. Such discoveries have improved our understanding of fern evolution and informed classification efforts, whether they have ultimately led to an increase (e.g. dissolution of Blechnum s.l.; Perrie et al. 2014; Gasper et al. 2017) or a decrease (e.g. union of Eriosorus and Jamesonia; Sánchez-Baracaldo 2004) in the number of recognized genera.
***A brief aside – the Lastreopsis taxa mentioned were found both by Gardner et al. (2017) and Perrie et al. (2021b) to be clearly nested within Lastreopsis, and no new genus name was ever proposed to accommodate them. I point this out as it is relevant to this and possibly to future proposals.
Testo et al. (2019), Chen et al. (2020), and Perrie et al. (2021) all concur that data available at this time are not sufficient to confidently assign these unplaced species to the genera defined by Testo et al. (2019), other lineages within the lecanopteroid ferns, or to another clade of subfamily Microsoroideae altogether. I think that is OK. As I see it, decisions about generic classification should be made based on available data, and generic circumscriptions can (and should) be re-evaluated as new data become available.
Regional versus global perspectives on fern classification:
Perrie et al.’s argument for expanding Lecanopteris to include Zealandia and Dendroconche is based in part on the premise that these lineages rarely overlap geographically, thereby minimizing disruption and confusion for workers in a given country or region. As I understand it, this point argues that the disruption of the traditional circumscription of Lecanopteris at a global scale will not significantly impact a worker based in New Zealand, for example, because they previously did not have any Lecanopteris species in their flora, so they have a “fresh slate”, so to speak. Similarly, someone working in Malaysia would not be seriously inconvenienced, Perrie et al. argue, because all but one of the species of a newly expanded Lecanopteris in their flora had been treated in that genus already.
While I do not agree with Perrie et al.’s point that it is inconsequential to lump readily distinguishable groups because workers in one region or another may not notice much of a difference (in that case, why not re-circumscribe Salpichlaena to include Stenochlaena and Telmatoblechnum?), I think that is is more important to note that such a viewpoint appears to be incompatible with the goals of PPG2. Attempts at developing coherent classifications for ferns in the modern era (e.g., Smith et al., 2006; Christenhusz & Chase, 2014; PPG1, 2016) have had a global scope, and PPG2 is no exception. PPG2 is a global community effort includes nearly 200 participants from dozens of countries, and there is good reason to expect that the classification we develop will be widely adopted by users from around the world for applications that are often global in scope. Of course, some users may opt for alternative classifications that are framed by regional or national perspectives on plant diversity; nonetheless, I do not think such views should inform the PPG2 approach to classification.
For these reasons, I will be voting against the recognition of an expanded Lecanopteris and in favor of the recognition of Bosmania(#27), Dendroconche(#27), and Zealandia(#26).
-- Wes Testo
References
Bosman, M. T. M. 1991. A monograph of the fern genus Microsorum (Polypodiaceae) including an attempt towards a reconstruction of the phylogenetic history of the microsoroids. Leiden Botanical Series, 14: 1–161.
Chen C-C, Hyvönen J, Schneider H. 2020. Exploring phylogeny of the microsoroid ferns (Polypodiaceae) based on six plastid DNA markers. Molecular Phylogenetics and Evolution 143: 106665.
Christenhusz, M. J., & Chase, M. W. 2014. Trends and concepts in fern classification. Annals of botany, 113: 571–594.
Gardner, J. J., Perrie, L., Shepherd, L., & Nagalingum, N. S. 2017. Taxonomic placement of unassigned species of lastreopsid ferns (Dryopteridaceae) using phylogeny. Systematic Botany 42: 385–391.
de Gasper, A. L., Almeida, T. E., Dittrich, V. A. D. O., Smith, A. R., & Salino, A. 2017. Molecular phylogeny of the fern family Blechnaceae (Polypodiales) with a revised genus‐level treatment. Cladistics, 33: 429–446.
Kreier, H. P., Zhang, X. C., Muth, H., & Schneider, H. 2008. The microsoroid ferns: Inferring the relationships of a highly diverse lineage of Paleotropical epiphytic ferns (Polypodiaceae, Polypodiopsida). Molecular Phylogenetics and Evolution, 48: 1155–1167.
Nooteboom, H. P. 1997. The microsoroid ferns (Polypodiaceae). Blumea: Biodiversity, Evolution and Biogeography of Plants, 42: 261–395.
Perrie, L. R., Wilson, R. K., Shepherd, L. D., Ohlsen, D. J., Batty, E. L., Brownsey, P. J., & Bayly, M. J. 2014. Molecular phylogenetics and generic taxonomy of Blechnaceae ferns. Taxon, 63: 745–758.
Perrie L.R., Field A.R., Ohlsen D.J., Brownsey P.J. (2021) Expansion of the fern genus Lecanopteris to encompass some species previously included in Microsorum and Colysis (Polypodiaceae) Blumea 66: 242–248.
Perrie, L. R., Amice, R., Shepherd, L. D., & Brownsey, P. J. (2021B). Lastreopsis abscondita (Dryopteridaceae), a new fern species endemic to New Caledonia. New Zealand Journal of Botany, 59(3), 409-422.
PPG 1. 2016. A community‐derived classification for extant lycophytes and ferns. Journal of systematics and evolution, 54: 563–603.
Sánchez‐Baracaldo, P. 2004. Phylogenetics and biogeography of the neotropical fern genera Jamesonia and Eriosorus (Pteridaceae). American Journal of Botany, 91: 274–284.
Smith, A. R., Pryer, K. M., Schuettpelz, E., Korall, P., Schneider, H., & Wolf, P. G. 2006. A classification for extant ferns. Taxon, 55: 705–731. Testo W.L., Field A.R., Sessa E.B., Sundue M. (2019) Phylogenetic and Morphological Analyses Support the Resurrection of Dendroconche and the Recognition of Two New Genera in Polypodiaceae Subfamily Microsoroideae Systematic Botany 44(4): 1–16.
leonperrie
joelnitta
Author(s) of proposal
Ashley Field
Name of taxon
Lecanopteris
Rank of taxon
Genus
Approximate number of species affected
12
Description of change
Perrie et al. (2021) re-circumscribed the genus Lecanopteris Reinw. based on a further morphological and philosophical appraisal of the phylogenies of Testo et al. (2019) and Chen et al. (2020). Lecanopteris was broadened to include the recently resurrected and recircumscribed genus Dendroconche and recently described genus Zealandia to achieve monophyly from a previously paraphyletic Microsorum and Colysis. The abstract of Perrie et al. (2021) is reproduced below:
"The fern genus Microsorum is not monophyletic, with previous phylogenetic analyses finding three lineages to group not with the type species, but to form a grade related to the 13 species of Lecanopteris. These three lineages have recently been recognised as separate genera: Bosmania, Dendroconche, and Zealandia. Here, we explore the morphological characterisation of Lecanopteris and these other three lecanopteroid genera. While the\ traditional circumscription of Lecanopteris has seemed sacrosanct, its defining morphological character states of rhizome cavities and ant brooding associations occur in other lecanopteroid ferns and elsewhere in the Polypodiaceae. Instead, we suggest that the morphological characterisation of an expanded Lecanopteris including the Dendroconche and Zealandia lineages is just as good, if not better, with the pertinent character states being the absence of sclerenchyma strands in the rhizome and at least some fronds having Nooteboom's type 5 venation pattern. This wider circumscription is also better able to accommodate phylogenetic uncertainty, and it means that groups of species traditionally placed together in a single genus are not distributed across different genera. General users familiar with the narrower circumscription of Lecanopteris will not be significantly disrupted, because there is little geographic overlap with the lineages added to the genus. Consequently, we make new combinations in Lecanopteris for 11 species and one subspecies."
Reason for change
Multiple studies have shown that Microsorum and Colysis as adopted in PPG I (2016) were paraphyletic. This proposal is directed at achieving monophyly among relevant genera by recognition a broadly circumscribed Lecanopteris subsuming the recently described Dendroconche and Zealandia but not Bosmania. This proposal should be read in conjunction with proposals for Bosmania + Dendroconche + Lecanopteris s.s. + Zealandia sensu Testo et al. (2019) (#25, #26, #27).
This proposal affects approximately 12 species occurring across Oceania. It was adopted World Ferns. It should be compared to the contrasting three-genus classification presented by Testo et al. (2019).
Reference(s) for publication of the name
Perrie L.R., Field A.R., Ohlsen D.J., Brownsey P.J. (2021) Expansion of the fern genus Lecanopteris to encompass some species previously included in Microsorum and Colysis (Polypodiaceae) Blumea 66: 242–248.
See also:
Chen C-C, Hyvönen J, Schneider H. 2020. Exploring phylogeny of the microsoroid ferns (Polypodiaceae) based on six plastid DNA markers. Molecular Phylogenetics and Evolution 143: 106665.
Testo W.L., Field A.R., Sessa E.B., Sundue M. (2019) Phylogenetic and Morphological Analyses Support the Resurrection of Dendroconche and the Recognition of Two New Genera in Polypodiaceae Subfamily Microsoroideae Systematic Botany 44(4): 1–16.
List the numbers of any related issues
25, #26, #27
Code of Conduct