From Plant Press, Vol. 21, No. 1, January 2018.
By Eric Schuettpelz
Typical fern spores are less than one tenth of a millimeter in diameter and are readily carried to far off places by the wind. Having such small propagules certainly contributes to the disproportionate diversity of these plants on oceanic islands. Although ferns and lycophytes (collectively pteridophytes) only account for about 4 percent of the world’s vascular plant species, they can easily represent 20 percent of the species on islands. Generally speaking, the more isolated the island, the more disproportionate the contribution of pteridophytes.
Located in the southern Pacific, about 5000 km from North America and more than 7000 km from Australia, the Marquesas Islands are farther from a continental land mass than any other archipelago. The constituent islands are well separated from the rest of French Polynesia and about 1400 km from Tahiti and the rest of the Society Islands. The 12 major Marquesas Islands are nearly all volcanic in origin, ranging in age from about 1 to 6 million years old. In total, the archipelago accounts for about 1050 km2 of land area, which is roughly the same as the city of Los Angeles or the island of Tahiti and less than the Hawaiian island of Kaua’i. Three of the islands reach an elevation exceeding 1200 m.
A comprehensive flora of the Marquesas Islands has yet to be published. However, researchers based at the National Tropical Botanical Garden (led by David Lorence), the Smithsonian Institution (led by Warren Wagner), and the Institut de Recherche pour le Développement (led by Jacques Florence) have been studying the plants inhabiting this archipelago for more than three decades. Much of their progress has been tracked on the Flora of the Marquesas website and this information is currently being developed into a two volume Flora of the Marquesas Islands to be published in late 2018. At present, 329 native vascular plant species are listed. Remarkably, ferns and lycophytes account for 99 (30 percent) of these. There are very few islands or archipelagos with proportions that are more skewed toward pteridophytes.
As a first step toward understanding the origins of this incredible pteridophyte diversity, I recently traveled to the Marquesas Islands, with funding from the Global Genome Initiative and the National Science Foundation, to collect herbarium specimens and silica-dried material for DNA extraction. I was joined by Ken Wood (National Tropical Botanical Garden) and Jean-François Butaud (Consultant in Forestry and Polynesian Botany).
The three of us met on the island of Tahiti late on October 28th and departed for the Marquesas early the next morning. After a short connection on the island of Nuku Hiva, the largest of the Marquesas Islands, we made our way via a small Twin Otter aircraft to Ua Pou, a somewhat smaller island characterized by its rocky pillars. The summit of one of these pillars, Oave, at 1203 m, is among the highest points in the Marquesas.
We spent nine full days on Ua Pou, collecting pteridophytes, bryophytes, lichens, and even some flowering plants. The bulk of our time was spent in the higher parts of the island, which were generally accessible only by foot. We circled Poumaka, a prominent 500 m tall spire, and collected on the steep ridges and in the deep valleys around Poutetainui and Tekohepu. We also spent a considerable amount of time on the slopes adjacent to Oave, where Jean-François Butaud collected what are most likely two new species in the genera Pilea (Urticaceae) and Kadua (Rubiaceae). The pteridophytes on Ua Pou did not disappoint. We encountered large tree ferns (e.g., Alsophila tahitensis and Sphaeropteris medullaris) with leaves several meters in length, diminutive filmy ferns (e.g., Crepidomanes minutum and Didymoglossum tahitense) with leaves smaller than 1 cm, and everything in between.
Left: Poutetainui (foreground) and the Ua Pou airstrip (background). (photo by Jean-François Butaud)
Right: Jean-François Butaud (at red arrow) collects what is most likely a new species of Pilea from the slopes below Oave. (photo by Eric Schuettpelz)
On November 8th, we left Ua Pou for the somewhat larger island of Hiva Oa, where we spent seven full days. Much of our time on Hiva Oa was spent in the cloud forests in the vicinity of Temetiu, which, at 1276 m, is the highest point in the Marquesas. At the higher elevations, we encountered an impressive array of grammitid ferns (nine species in eight genera) among many other pteridophytes. Overall, on Ua Pou and Hiva Oa together, we collected 82 of the 99 pteridophytes species indigenous to the Marquesas Islands (based on our field determinations). Of the 17 species we missed, 11 had never been collected from either Ua Pou or Hiva Oa.
Fieldwork is never without at least a few unexpected logistical challenges, and this trip was no different. As our initial supply of newspaper, the preferred material for preserving botanical specimens, was quickly depleted over the course of a few days on Ua Pou, we sought to restock. Usually, this is a trivial endeavor, with plenty of options in various sizes piled up and awaiting reuse or recycling. However, none was to be found, for free or even for sale, on the island of Ua Pou. As it turns out, the sole distributor stopped bringing newspapers to the island a couple of years prior, presumably due to decreased demand as residents were increasingly able to access information on their mobile phones. Thankfully, we were able to quickly arrange for a dispatch from Tahiti of La Dépêche de Tahiti.
Left: Oleandra sibbaldii. (photo by Eric Schuettpelz)
Right: A windblown individual of the tree fern Sphaeropteris feani. (photo by Ken Wood)
In the end, our team made a total of 306 collections of lichens, bryophytes, pteridophytes, and flowering plants. Each collection consisted of several duplicate herbarium specimens, plus silica-dried material. The more than 1000 duplicates we collected will be distributed to herbaria in Kalaheo (PTBG), Papeete (PAP), Paris (P), Réunion (REU), and Washington, D.C. (US). The silica-dried material, in turn, will be stored in the National Museum of Natural History biorepository. These botanical specimens and the accompanying silica-dried material will form the foundation for a variety of future evolutionary studies focused on oceanic plants as we continue to leverage the long history of collaboration between the Smithsonian Institution and the National Tropical Botanical Garden.
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