First records of Tall Beech Fern, Phegopteris excelsior N. Patel & A.V. Gilman (Thelypteridaceae), for Ontario and Prince Edward Island

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n° 29, 
juin 11, 2024


A tetraploid Beech Fern has been known from the flora of northeastern North America since the 1970s but its cryptic nature has contributed to it being incompletely understood. It was first considered a hybrid between Phegopteris connectilis (Michx.) Watt and P. hexagonoptera (Michx.) Fée (Mulligan et al. 1972), and later lumped within a broad circumscription of P. connectilis (Mulligan and Cody 1979). Driscoll et al. (2003) noted that isozyme and additional morphological data were inconsistent with a hybrid between P. connectilis and P. hexagonoptera, and instead suggested a hybrid origin involving P. connectilis and another unknown species. This hypothesis was supported by by Patel (2018) using plastid and nuclear data. Finally, P. excelsior was described at specific rank by Patel et al. (2019a), with confirmed occurrences ranging from New York and Connecticut to Quebec and Nova Scotia. We report the first records for Ontario and Prince Edward Island, which contribute to its known range, including a roughly 420 km western range extension from Rougemont, Quebec to Algonquin Provincial Park, Ontario. These records were uncovered during field work and subsequent review of Ontario P. connectilis specimens housed in CAN and DAO.

Results and Discussion

Phegopteris excelsior and P. connectilis are very similar and there is overlap in the distinguishing morphological characters, so we placed particular emphasis on spore size for species determination (see Patel et al. 2019a for measurements). Phegopteris excelsior tends to have spaces between all of its pinnae (Fig. 1), whereas in P. connectilis they are closer together, with their pinnae filling the frond's plane (Gilman 2020). We found this feature particularly helpful in the field and herbarium as a rapid character to select candidate P. excelsior, which we then verified by taking spore measurements using scanning electron microscopy. We aimed to image and measure at least 10 spores from each specimen. The images for Chapman-Lam 5753 did not show enough spores, but it is one of several P. excelsior collections made in Bilberry Creek, making the species otherwise well documented from the site. Overall, average spore length in our P. excelsior collections ranged between 62.54 – 69.95 μm, with extreme minimum and maximum lengths of 54 and 80 μm, respectively (Table 1). Patel et al. (2019b) summarised spore ornamentation in the Thelypteridaceae, which can sometimes help distinguish taxa. No distinctions in perine morphology between P. connectilis and P. excelsior were readily apparent to us (Fig. 2), although this was not a focus of our study.

The ecological conditions at these newly reported P. excelsior sites are consistent with those previously reported (Patel et al. 2019; Gilman pers. comm. 2023). Generally, the new records are from deeply shaded toe slopes, on banks just above streams or lakes. The Algonquin Park specimen differs in being collected from igneous rock along a road cut. If north-facing, it could possibly provide similar cool conditions.

More work is required to determine the distribution, abundance, and conservation status of P. excelsior. NatureServe (2024) has calculated some provincial status ranks in Canada (see Master et al. 2012 for rank definitions): P. excelsior is considered of conservation concern in Quebec, where its provincial status rank is S3? (Vulnerable), and in Prince Edward Island it has now been ranked S1S3 (Critically Imperilled to Vulnerable). However, NatureServe (2024) has not yet provided an overall global status rank, and its rank is either SU or SNR (Unrankable or Not Ranked) in nearly all provinces and states where it is known. This indicates a high degree of uncertainty around its conservation status both in those jurisdictions and globally. The discovery of three widespread eastern Ontario occurrences demonstrates we have much to learn in Ontario as well. Its habitat is much more widespread than the presently documented distribution of P. excelsior, suggesting there could be additional occurrences elsewhere in central and northern Ontario.


The Ontario field work was supported in part by the Ottawa Field Naturalists’ Club. The initial PEI field work was conducted by Colin Chapman-Lam for the Atlantic Canada Conservation Data Centre, with support from the PEI Forested Landscape Priority Place for Species at Risk. The following people kindly helped with loans and specimens: Lyndsey Sharp, Nathan Stevens-Cocco, and Jennifer Doubt at CAN, and Shannon Asencio and Kelsey Joustra at DAO.




Driscoll, H.E., D.S. Barrington and A.V. Gilman. 2003. A reexamination of the apogamous tetraploid Phegopteris (Thelypteridaceae) from northeastern North America. Rhodora 105: 309–321.


Gilman, A.V. 2020. Tall Beech Fern, A new beech fern in New England, New York, and Canada. Unpublished document. 16 pp.


Master, L., D. Faber-Langendoen, R. Bittman, G.A Hammerson, B. Heidel, L. Ramsay, K. Snow, A. Teucher, and A. Tomaino. 2012. NatureServe Conservation Status Assessments: Factors for Evaluating Species and Ecosystem Risk. NatureServe, Arlington, VA.


Mulligan, G.A. and W.J. Cody. 1979. Chromosome numbers in Canadian Phegopteris. Canadian Journal of Botany 57: 1815–1819.


Mulligan, G.A., L. Cinq-Mars & W. J. Cody. 1972. Natural interspecific hybridization between sexual and apogamous species of Phegopteris Fée. Canadian Journal of Botany 50: 1295–1300.


NatureServe. 2024. Network Biodiversity Location Data accessed through NatureServe Explorer. NatureServe, Arlington, Virginia. Available (accessed: 2024-02-27).


Patel, N.R. 2018. Apomixis, Hybridization, and Biodiversity in Ferns: Insights from Genera Phegopteris and Polystichum. Ph.D. Thesis, University of Vermont, Burlington


Patel, N.R., S. Fawcett, and A.V. Gilman. 2019a. Phegopteris excelsior (Thelypteridaceae): A new species of North American tetraploid beech fern. Novon 27(4): 211-218.


Patel, N., S. Fawcett, M. Sundue, and J.M. Budke. 2019b. Evolution of perine morphology in the Thelypteridaceae. International Journal of Plant Sciences 180(9): 1016–1035.


Collection No. Accession No. Spore length (µm)
Min. Avg. Max. N
Chapman-Lam 5711 CAN10177022 54 63 73 16
Chapman-Lam 5712 CAN10177023 57 67 77 11
Chapman-Lam 5751 CAN10177024 58 65 70 11
Chapman-Lam 5753 CAN10177026 61 67 74 8
Chapman-Lam 5754 CAN10177027 60 68 74 14
Klymko & O'Connor JKBOT18 CAN10186752 63 70 80 15
W.J. Cody 21453 DAO01-01424857 55 63 69 11
F.W. Grimm s.n. DAO01-01424896 60 67 76 10 



Fig. 1. Phegopteris excelsior at Bilberry Creek, ON, August 30, 2022. Note the space between the pinnae.


Fig. 2. SEM micrographs of spores from (A) Phegopteris connectilis [Chapman-Lam 5752] and (B) Phegopteris excelsior [Chapman-Lam 5754]. Scale bars are 30 µm (A) and 50 µm (B).