Phegopteris excelsior (Thelypteridaceae): A New Species of North American Tetraploid Beech Fern

Abstract

Since the 1970s, an apomictic tetraploid beech fern (genus Phegopteris (C. Presl) Fée) has been known in northeastern North America. Previously published isozyme data suggest that this lineage is of allopolyploid origin involving long beech fern (P. connectilis (Michx.) Watt.) but not broad beech fern (P. hexagonoptera (Michx.) Fée), as originally hypothesized. Its second progenitor remains unknown. We performed a principal components analysis of the apomict and its North American congeners to elucidate morphological differences between them. We recognize the apomictic tetraploid at specific rank as P. excelsior N. R. Patel & A. V. Gilman and provide an illustration, a range map, a list of exsiccatae, and a key to Phegopteris species of North America.

Cryptic diversity in the model fern genus Ceratopteris (Pteridaceae)

“…Compared to seed plants, ferns have a very high prevalence of polyploidy and reticulate evolution (Barrington et al 1989;Paris et al 1989;Otto and Whitton 2000;Otto and Whitton 2000). Such genomic changes can contribute to cryptic variation by altering niche requirements or offspring viability (Otto 2007;Southgate et al 2019;Masuyama et al 2002), yet be essentially phenotypically invisible (Patel et al 2019).…”

A fossil beech fern (cf. <i>Phegopteris</i> (C. Presl) Fée) from Driftwood Canyon Provincial Park, British Columbia

“…It is unclear whether the lowermost pair of pinnae is present on the fossil beech fern, and the attachment of the lowermost pinna to the rachis is poorly preserved (Figure 2b). However, if the lowermost pinna is interpreted as part of the lowermost pinna pair, it is symmetrical, as seen in P. con nectilis (Patel et al 2019), but lacks the basioscopic orientation (Figure 2a,b) typical of the P. connectilis group. It is unclear whether laminal wings joined this pinna to the one above it or whether the rachis was unwinged, as seen in P. connectilis and P. excelsior (Patel et al 2019).…”

“…However, if the lowermost pinna is interpreted as part of the lowermost pinna pair, it is symmetrical, as seen in P. con nectilis (Patel et al 2019), but lacks the basioscopic orientation (Figure 2a,b) typical of the P. connectilis group. It is unclear whether laminal wings joined this pinna to the one above it or whether the rachis was unwinged, as seen in P. connectilis and P. excelsior (Patel et al 2019). Marginal exindusiate sori-diagnostic of Phegopteris-are absent on the specimen, preventing definitive assignment of the specimen to Phegopteris and to a species (e.g., Stockey et al 2006).…”

“…The distal portion of the fern blade in P. connectilis (Figure 2a), and less so in P. excelsior, narrows abruptly to a pinnatifid tip, whereas, in P. hexagonoptera, the blade narrows evenly toward the tip as seen in the fossil (Figure 2b). Patel et al (2019) separated P. connectilis from P. excelsior on the basis of the "tear-shaped" outline of the whole blade versus the broadly deltoid shape of P. excelsior and from P. hexagonoptera by the prominent basioscopically (downward) pointing and asymmetric lowermost pair of pinnae in that species, with P. con nectilis pinnae symmetrical and P. excelsior intermediate between these states. It is unclear whether the lowermost pair of pinnae is present on the fossil beech fern, and the attachment of the lowermost pinna to the rachis is poorly preserved (Figure 2b).…”

“…The Thelypteridaceae contains two subfamilies, Phegopteridoideae and Thelypteridoideae, with the former containing three genera, including Phego pteris, with seven species (PPG I 2016;Patel et al 2019;Fujiwara et al 2021) 2b-d). The fossil has nine lanceolate, free, pinnae pairs on an incompletely preserved fossil leaf blade with the lowermost preserved pair also incomplete versus P. connectilis, P. excelsior, and P. hexa gonoptera with 12-15 pairs.…”