Switzerland/Austria/Italy 2018
If you're interested in fern biology, you've probably discovered that western Europe has the world's highest density of fern fanatics. A quick scan of the British Pteridological Society Bulletin, Fern Gazette or Pteridologist, for example, makes this quite clear - they are full of field trip reports ("Ferns of Colsterdale, west of Masham, Yorkshire Dales"), observations on unusual forms of common species ("Comparing the frills"), and other fun titles ("Unusual urban site for Adiantum capillus-veneris"). Put simply, our European counterparts really love their ferns and set a global standard for knowledge about the diversity and distribution of ferns in their part of the world. This intimate knowledge of the plants is reflected in the taxonomy of certain genera of European ferns, especially the wood ferns and the spleenworts. Unlike their counterparts in most other parts of the world, who generally seem content to lump all infraspecific entities together, European pteridologists have levied a carefully constructed and finely cut taxonomy on some troublesome groups, often with forms nested within varieties that themselves nested within subspecies. I have always admired the attention to detail exhibit by our European colleagues, but without the plants in front of me, have not been able to evaluate their taxonomic schemes for myself. Without further information, I had settled on three possibilities: 1) our European friends were willing to slice off any morphological variant as a new taxon (a la Hieracium?), 2) we Americans lacked the attentiveness to pick up on cryptic diversity in our own ferns (with some obvious exceptions: cheilanthoids and Botrychium for two) or 3) there simply was an exceptional amount of cryptic diversity in some European fern genera, analogous to our own Myriopteris or Botrychium.
Perhaps the most complicated group of European ferns is the Dryopteris affinis complex, which is comprised of perhaps two dozen taxa recognized at various ranks. The group extends from the Middle East westwards through Europe and into some Atlantic islands but the center of the described diversity is firmly in central and western Europe. The taxa comprising the group are exceptionally similar to each other and morphological characters that consistently define and separate taxa are hard to come by. The difficulty in distinguishing the members of the complex appears to be principally due to considerable variation in ploidy and reproductive mode: diploids, triploids, tetraploids, pentaploids, and hexaploids are known and apomixis is widespread. To complicate this further, the apomictic taxa (which typically skip sexual reproduction in favor of spontaneous generation of a sporophyte from a gametophyte of the same ploidy) frequently hybridize with closely related sexual species, presumably via functional sperm. There is even evidence that individual sporophytes can produce spores of different ploidy levels (Ekrt et al 2015)! With all this considered, it is no surprise that considerable discomfort remains among the European pteridological community on which taxa to recognize and at what rank.
I've been interested in some peripheral members of the Dryopteris affinis group (Mexico's Dryopteris pseudofilix-mas and the pantropical Dryopteris wallichiana, to name two) for several years now, so I was thrilled when Michael Kessler (University of Zurich, Switzerland) reached out about including members of this group in the sampling for the ongoing GoFlag phylogenomics project that I am working on as a post-doc. Even better, Michael suggested that my postdoc advisor Emily Sessa and I visit Switzerland to join a large collecting expedition aimed at the Dryopteris affinis group (and some other taxa) this summer. Given my curiosity about this seemingly intractable species complex, Emily's love for the genus (her PhD focused on Dryopteris systematics and functional ecology, and she continues working on the group), and the fact that it meant doing fieldwork in the Alps, it was a no-brainer to take up his offer. How bad could these taxa be?
Fortunately for us, Michael planned the itinerary, which was organized with input from two German experts (Jens Freigang and Günther Zenner) who are experts in the group. The trip would take us from Zurich, through western Austria, into northern Italy, and then return to Zurich through south-central Switzerland. We would cover around 1000 kilometers and spend five days in the field with a total of twelve people representing Chile, Germany, Switzerland, and the USA. The general sampling approach was simple: find as many members of the Dryopteris affinis group as possible and collect herbarium vouchers, material for flow cytometry, and additional material for generating DNA sequence data. Naturally, I wanted to be in the field with these taxa to see if I could tell them apart.
After a brief meet-up in Zurich with Michael, Marcus Lehnert (the world's foremost expert in tree fern taxonomy) and Michael's student Daniela, we headed two hours east to Vorarlberg, Austria’s westernmost state. Here, we met with the rest of the crew on the side of a logging road in the mountain. Within minutes, we were onto the ferns – first the lady fern, Athyrium filix-femina and the male fern, Dryopteris filix-mas. Taking a close look at each of them, it was hard to believe that they are conspecific with the plants we call those names in North America; this is especially clear for the male fern, which is much more robust and common in Europe than its North American counterpart ever is. Certainly, there are plenty of overlooked (or ignored) cryptic fern taxa in even the best-studied regions – these strike me as two obvious examples.
While I mulled over these differences, we were onto what we came for: the Dryopteris affinis complex. The first representatives of the we saw were Dryopteris borreri (apomictic triploid) and Dryopteris affinis subsp. punctata (sexual diploid) – several plants of each taxon on a rocky slope just meters from where we parked our cars. I found the latter taxon to be fairly distinctive: true to its name, it has prominent vein endings that form punctations in its thick, deep green lamina. Dryopteris borreri, on the other hand, seemed to be everywhere and was (as best I could tell) defined mostly by lacking the characters of the other species. Other, more familiar ferns were scattered on the rocks here, too: Polystichum lonchitis, Polypodium vulgare, and Asplenium adiantum-nigrum. We stuffed bags full of the Dryopteris for herbarium vouchers and molecular analyses, and then moved on.
We started up the gravel road, following local Dryopteris experts Jens and Günther and taking some time to enjoy the abundant raspberries and the odd lady fern here and there. Jens pointed at a large Dryopteris on the side of the road ahead of us and IDed it as Dryopteris cambrensis subsp. insubrica (apomictic triploid) – from 20 yards away. We looked at it as he listed off its definitive characteristics and shrugged – maybe it’s different!? We continued along and found more members of the group: D. borreri var. robusta (apomictic triploid), D. pseudodisjuncta (apomictic triploid), and the hybrid between D. filix-mas and D. affinis subsp. punctata. It was fascinating and overwhelming; they all started to blend together in my mind. We took a break from these with more familiar taxa growing on a nearby talus slope: Dryopteris carthusiana (sexual tetraploid, convincingly like the American plants), Dryopteris dilatata (sexual tetraploid, essentially the European counterpart to the American Dryopteris campyloptera), and Dryopteris expansa (sexual diploid, not-so convincingly similar to the American plants under that name). Some fun non-ferns included Huperzia selago and Spinulum annotinum, which formed extensive colonies on the shaded slopes.
From Vorarlberg, we headed back west, crossing through Liechtenstein (!) and re-entering Switzerland, heading south towards Italy through the San Bernandino pass. After about 90 minutes in the car, the German-language signs yielded to Italian ones (and some in Romansh, Switzerland’s fourth official language!). After another hour weaving through spectacular alpine landscapes, we crossed into the plains of Lombardy, Italy. We soon arrived at our destination: Maccagno con Pino e Veddasca, a beautiful town with an absurdly long name on the shores of Lago Maggiore, Italy’s second-largest lake (after Lake Garda, another glacial lake about 150 km to the east). We checked in to our hotel, had excellent pizza (of course), and then got to work pressing plants. With decades of experience collecting large numbers of plants for elevational transects around the world, Michael and his group made quick work of the pile of Dryopteris – I managed to stuff some pinnae in envelopes for DNA extraction back home.
We started early the next day and made several stops in the field in both Switzerland and Italy (made easy by the Schengen Zone’s laissez-faire approach to border crossings). Top on our list was visiting a population of Dryopteris remota (apomictic triploid), a rather peculiar species thought to be derived from a cross between the diploid race of D. affinis subsp. affinis and D. carthusiana. Jens and Gunther led us to a large population on a forested hillside overlooking the Swiss-Italian border, though for once we all could have picked it out for ourselves – the large, broadly lanceolate and irregularly dissected leaves of this species were like nothing else we had seen on the trip. Instead, the plants reminded me of some D. carthusiana-derived hybrids that are familiar from North America, such as D. × uliginosa (sterile tetraploid) and D. × benedictii (sterile pentaploid). With D. remota in the bag, we started searching for D. × alpirsbachensis, the sterile pentaploid backcross between D. remota and D. carthusiana. After an hour of searching, we *possibly* found it, scattered amongst dozens of D. carthusiana. More detailed study is needed to confirm our field hypothesis – fingers crossed. There were plenty of other good ferns here, too: Asplenium scolopendrium, Polystichum aculeatum, and Asplenium adiantum-nigrum, to name a few. We stopped at a few other sites nearby and found some other gems, including Polystichum braunii (which is quite rare in that part of Europe) and Dryopteris affinis subsp. affinis, which was growing scattered amongst its close relative, Dryopteris affinis subsp. punctata. A cold ran materialized from the mountain pass above us and chased us back to Italy, where we could study the plants without our hand lenses fogging up. After two full days in the field with these plants, I was starting to see the differences between them, but I wasn’t sure that the North American community of botanists would accept such finely separated taxa as distinct if these plants were growing on the other side of the Atlantic.
For our last day in the field, we drove 100 km back into Swiss territory, where we got off the highway near the town of Quinto and began a slow ascent up a series of continuously narrowing switchbacks to Lago Ritòm, a spectacular alpine lake (with attached hydroelectric dam) perched in a narrow mountaintop valley. Our quarry here was an odd member of the Dryopteris dilatata complex that Jakob (Swiss fern expert in our group) had found there several years before. The plant was strange because it resembled Dryopteris dilatata but Jakob had counted its chromosomes and found it to be diploid (D. dilatata is tetraploid). Only one diploid member of the D. dilatata group was known in the area (D. expansa) and everyone who had seen this plant before seemed to be sure it was not that species, which is subtly distinct in the shape of its leaves and the color of the scales covering its rhizome. The notion that there was some yet-unknown fern growing along a rather well-explored Swiss lake should have struck me as hard to believe, but after three days with the Dryopteris affinis group I believed anything was possible.
While the rest of us were still walking along the edge of the lake, Jakob scrambled down from some wooded bank (this was a common occurrence by now) with a leaf of the mystery plant. The group passed it around and exchanged glances -some seemed to know by smell that this plant was “the plant,” others were content to recognized it as a Dryopteris – and we set off to see the plant in situ. Once we entered the woods, Jakob and the other local Dryopteris experts started to sort through the dozens of ferns around us: dilatata, dilatata, another dilatata, mystery plant, another dilatata. As with the Dryopteris affinis aggregate, the differences were small but real. The mystery diploid plant differed from the more abundant Dryopteris dilatata in leaf color and texture as well as something about the presentation of the leaves (flow cytometry would later confirm our field determinations). We spent about an hour looking at the plants and making a few collections, forming a rather comical human chain to pass collection bags and leaf samples up and down the slope. In the background, a well-caffeinated Jens scampered about, identifying every Dryopteris on the mountain. We took some photos and headed back down to the lake for some lunch.
After lunch, we walked to the other side of the lake to look for Botrychium in some pastures but were unable to find them – we surmised that the ephemeral plants had either died-back for the season or they were all eaten by cows, which apparently is a thing that happens in Switzerland. Our consolation prizes were Gymnocarpium robertianum, Dryopteris borreri (which I am proud to say I picked out from a distance of twenty feet), and Asplenium septentrionale, a peculiar spleenwort that looks like a tuft of grass. On the way back to the parking lot, we spotted a large population of Selaginella selaginoides atop a rock wall; we made a few collections (every herbarium needs more lycophytes!) and then headed back to the cars. We were headed for the town of Härkingen some two hours to the north, but made another stop halfway to see Asplenium scolopendrium, Polystichum setiferum, and an undescribed member of the Dryopteris affinis complex.
We arrived in Härkingen around 8pm, just as a cold rain began to fall. We had reservations at what must be one of the most unique lodgings in Switzerland – Alte Gärtnerei, a bed and breakfast built into a greenhouse. We found out about the place because two members of our group (Maria and Michael) own a fern nursery that is run out of some of the greenhouses on the property, and the place was perfect for our group. Ernst, who runs the B&B with his wife, Rita, ordered us pizzas from a local restaurant while we settled in. We were too tired to process the plants we had collected that day, so we kept them in bags and instead elected to enjoy a few beers and admire a robust plant of ×Cystocarpium roskamianum that Michael and Maria brought over from their greenhouse. ×Cystocarpium is a fascinating plant: as demonstrated by Carl Rothfels and colleagues in a very nice paper published in American Naturalist in 2015, it is an intergeneric hybrid between Cystopteris fragilis and Gymnocarpium dryopteris, two species which belong to lineages that diverged some 60 million years ago. Only one individual of ×Cystocarpium is known, and the plant we were looking at was propagated from that clone. Despite holding two very different parental genomes within it, the plant seemed quite robust and not hindered by its inability to produce viable spores.
We spent the following morning visiting the greenhouses of Michael and Maria, where they cultivate more than 600 species of ferns from around the world. It was a spectacular setup, and I got to see a lot of species that were new for me. In addition to impressive holdings of native Swiss ferns, they seemed to have a strong interest in several groups of tropical ferns, including the perennially popular staghorn ferns (Platycerium) and the ant ferns (Lecanopteris). They were generous enough to let me sample from their collections for our ongoing flagellate plants phylogenomics project (GoFlag), and I was glad to be able to help them out some with the identification of a few species. Härkingen is about halfway between Zurich and Bern and only an hour northwest of Lucerne, so if you are in the area, definitely check out the Farnwerk garden and consider staying at Alte Gärtnerei!
That afternoon, said goodbye to Michael and Maria and headed back to Zurich, where most of the rest of the group disembarked after we finished processing the last of our samples. I stayed for a few more days, working with members of the Kessler lab on some collaborative projects. Best of all, I got to flip through the Dryopteris affinis collections again. This time, they all (okay, most of them) looked different. We'll see what the data say.