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' Carex arctogena'' Harry Sm. '''

The species Carex arctogena Harry Sm. is a member of the sedge family which grows in high alpine areas. It is one of the few species that is known to grow in a bipolar manner which allows for populations in Greenland, Scandinavia, Russia, Canada and southern South America to exist (1). Plants originating from different hemispheres appear to be genetically identical showing how they have taken advantage of niches at opposite sides of the globe.

It has often been confused with closely related Carex capitata and was originally classified as the same species until Harry Smith distinguished differences between the species in 1940(2,3). Defining morphological characteristic of this species include toothed scales which cover the female reproductive parts of the inflorescence, a larger seed relative to the size of the female reproductive sac (perigynia) and round perigynia which quickly tapers towards the apex. It will produce a single spike on each stem and have long elongated leaves which is characteristic for the genus Carex.

Description

Carex are a genus of sedges that lie within the Cyperaceae family, they resemble grasses with long simple stems, narrow leaves and a spike inflorescence (4). Inflorescences can be simple or compound, depending on whether there are one or more spikes, and can also be monoecious or dioicous depending on whether there are both sexes on the same plant or are found on different plants. (4)

C. arctogena has short rhizomes that new shoots and roots grow from, allowing it to grow in a cespitose manner. This means that it can be found growing in dense tufts amongst its habitat. (5,6)

This species produces vegetative shoots which become leaves, these are made up from a leaf sheath covering a culm. These will grow to be 1mm wide and have parallel veins running through the sheath. Sedges reproductive shoots are where the inflorescence grow from.(5) A specimen is typically between 10-30cm tall but may be closer to the former of this average as specimens of the sister species C. capitata are usually taller. (5)

Cyperaceae inflorescences grow from a stem called a culm, they are rigid and stand upright. The culm may exceed the height of the leaves only marginally, or by quite a lot, depending on the individual specimen and its habitat. At the base culms may appear reddish brown and at the terminus a single spike will grow. (5)

A spike will be made up from many florets. Basal florets consist of a pair of brown glumes (two sterile bracts) which subtend the perigynia (8). In C. arctogena the glumes can be recognised as brown and significantly smaller than those of its sister species(5).

Within a spike there will numerous perigynia, these perigynia are membranes which enclose female flowers and fruits. Each perigynia will be on average 1.7-2.7mm long and 1.2-1.7mm wide, forming a bottle-shape towards the open apex(6). In Carex this is termed a ‘beak’ and can be seen drastically tapering in C. arctogena compared to the perigynia’s otherwise reasonably rounded main body (6).

In Cyperaceae the perianth (sepals and petals) is often reduced or absent, which results in visible reproductive organs (4). In C. arctogena the perianth is absent meaning that only the style or stigma may protrude from the narrowed opening(4). The female flowers have two long thin stigmas which can appear red or brown(6). The ovary can be defined as superior (the ovary lies above the point of attachment for sepals, petals and stamens(7,8)

C. arctogena is monoecious, meaning that both pistilate (female) and staminate (male) flowers will occur on the same spike. This makes the whole sedge androgynous. The female flowers (multiple spikelets) will be arranged in a spherical shape around the centre of the spike, but nonetheless still pointing upwards no matter how marginally. Male flowers are sparsely arranged at the apex of the inflorescence, creating a conical projection at the top of the spike (4). Typically These characteristics can segregate C. arctogena from C. capitata as the spikelets will not be so erect and may point outwards, creating a less overall conical shape of the inflorescence.

A typical characteristic of C. arctogena are the pistilate scales on the perigynium. These cover almost the whole perigynia body but stop before it tapers at the apex. These can be seen under a microscope and appear white, with toothed margins(5). In C. capitata, the pistilate scales will be much shorter than the perigynia and will not appear toothed.

The fruit produced by C. arctogena is classed as an achene, which can be defined as a dry seed which has a thin wall (8). These characteristics make the seed light and enable it to be dispersed by wind. The presence of two stigmas equates to the fruit produced having two sides and being classified as lenticular(5). In this particular species the achene is larger in size relative to the size of the perigynia, meaning that it will almost completely fill this area. Whereas in C. capitata, the achene is considerably smaller than the area of the perigynium(6).

Etymology

Carex is the Latin word for sedge. It comes from the Greek word ‘kairo’ which means to cut, this refers to the long narrow leaves in which some species have sharp edges(16). The word “arctogena” is derived from the fact that this species can be found in the arctic region.

Habitat and ecology

This species has a bipolar distribution which means it can be found in both the northern and southern hemispheres of the world and can colonise many different locations. Within these locations the habitats usually consist of alpine areas at high altitude. Within its northern locality in Fremont County samples have been found on alpine summits at 8,500-1200ft (6). Whereas, within the arctic climate of Greenland specimens have been found at maximum altitudes of 250m (9).

Primarily this species prefers poor, lime soils and have also been known to grow in serpentine soils, these contain higher than average amounts of nickel, iron, cobalt and chromium (10). High alpine areas have large amounts of surface runoff from snowfields, meaning that the soil quality may be poor (3). Many herbarium specimens have been found on heathlands and grasslands located on hilltops. This creates a niche habitat for species which prefer little soil nutrients, and harsh winds (10). Due to the nature of it being an alpine plant, it is rarely found below the forest limit, meaning it grows only in forested areas of altitude.

C. arctogena can be distinguished from C.capitata as this species grows in lower alpine areas. It prefers moist calcareous soils and isn’t overshadowed by dense forest cover that higher altitudinal plants such as C. arctogena might reach and doesn’t have a bipolar distribution. Therefore, the habitat of C. capitata and C. arctogena rarely overlap and one can distinguish which species a specimen may be by observing morphological and ecological characteristics.

In the southern hemisphere C. arctogena occupies the same ecological niche as its northern populations. Although its distribution is smaller than that of the northern hemisphere as there are fewer optimal alpine areas.

Distribution

Carex arctogena has a bipolar distribution across arctic regions in the northern hemisphere and temperate regions in the southern hemisphere. This means that it can be found at high latitudes between >55˚N; >52˚S(1).

Within this range there are populations in the northern hemisphere that include:

-         Scandinavia: Norway, Sweden, Finland

-         Greenland

-         Canada: Labrador, Newfoundland, Manitoba, Nunavut, Ontario, Québec, Saskatchewan

-         Russia: Magadan

-          USA: California, Colorado, Wyoming, New Hampshire, Vermont

Southern hemisphere:

-         South America: Northwest and southern Argentina, Chile (2)

A study revealed haplotypes in C. arctogena which also occur in C. capitata, of which is only present in the northern hemisphere(1). From this we can assume that C. arcotgena was originally distributed in the northern hemisphere and more recently established populations in the South.

Taxonomy and systematics

The genus Carex was first described by Linnaeus in 1753 in the first edition of Species Plantarum. This was the first introduction of using the binomial naming system to classify plants. In this edition he described and distinguished between 29 species of Carex(13). Carex is a large paraphyletic genus with a cosmopolitan distribution containing around 2000 species. The species Carex capitata L. was described by Linnaeus in 1759 in System Naturae Volume two ‘Vegetabilia’.

The family Cyperaceae was recognised by Antoine Laurent de Jussieu and published in his ‘Genera Plantarum’ in 1789(7,12). It was only in 1821 that Samuel Frederick Gray placed the genus Carex within the family Cyperaceae. Today Cyperaceae contains 104 genera and around 5000 species, making it a large family.

In 1940 Harry Smith was the first to propose in ‘Acta Phytogeographica Suecica’ that there were two separate species within the species C. capitata L. He described differences in populations that he observed in Sweden, noticing small brown inflorescences compared to that of the larger green inflorescences of C. capitata. He created a set of characteristics that could be used to distinguish these two proposed specimens. Smith gathered samples from museums in order to analyse all of the found specimens, and was able to discreetly separate either specimen into C. arctogena n.sp (new species) or C.capitata sensu stricta (in the sense of: as C.capitata L. was described). Today when considering these two plants, literature considering C. capitata L. will be referring to both C. Capitata and C. arctogena Harry Sm(3).

Today the name Carex arctogena Harry Sm. is the accepted name for this species. Although during the last century many new taxonomic classifications were proposed. In 1944 Hiitonen proposed that C. arctogena should be classified as Carex capitata subsp. arctogena. This remark was also made by Böcher in 1952 but not accepted by taxonomists. In 1949 it was classified by Raymond as: Carex capitata f. arctogena, and in 1958 Hultén proposed C. arctogena be classified as a variety of C. capitata. None of these were widely accepted and today we have genetic evidence that these are in fact two distinct species. By conducting genetic analyses, we have verified that C. arctogena and C. capitata are of common origin. C. arctogena could have diverged recently as there is statistically no genetic variation, not even between specimens from the different hemispheres(10)

Type specimens are located at herbariums in N. Europe, New Hampshire, Argentina and Labrador.

Additional information

Only 30 species are known to have a bipolar distribution, a large proportion of which belong to the Cyperaceae family (14). It has been hypothesised that C. arctogena has been dispersed either by anthropomorphic introduction or by migratory birds. The seeds within this species have been found to contain silica deposits in the pericarp, this can help to make the seeds tougher (15). This could possibly mean that if eaten by a bird, the seed coat would not break down within its stomach and therefore would be passed out the other end and dispersed. Many birds are seed eaters and with the majority of bipolar plants belonging to Cyperaceae which produce seeds, this is a potential model for how these plants achieved a bipolar distribution.

References

1.      Villaverde, T., Escudero, M., Martín-Bravo, S., Bruederle, L., Luceño, M. and Starr, J. (2015). Direct long-distance dispersal best explains the bipolar distribution of Carex arctogena(Carexsect.Capituligerae, Cyperaceae). Journal of Biogeography, 42(8), pp.1514-1525.

2.      Plants of the World Online. (2019). ''Carex arctogena Harry Sm. | Plants of the World Online | Kew Science''. [online] Available at: http://powo.science.kew.org/taxon/45766-2 [Accessed 9 Oct. 2019].

3.      Smith, H (1940) ‘Carex arctogena nova species’, Acta Phytogeographica Suecica, vol. 13, pp. 191-200

4.      Böcher, T., Holmen, K., Jakobsen, K., Frederiksen, I., Elkington, T., Lewis, M. and Flora, G. (1968). The flora of Greenland. Cph. (tr. Odense): P. Haase, pp.218-231.

5.      Wilson, B., Brainerd, R., Lytjen, D., Newhouse, B. and Otting, N. (2014). Field guide to the sedges of the Pacific Northwest. 2nd ed. Oregon, pp.14-125.

6.      Hermann, F. (1970). Manual of the Carices of the Rocky Mountains and Colorado Basin. Washington: Forest Service, U. S. Department of agriculture, pp.16, 40-41.

7.      Simpson, M. (2010). Plant Systematics. Burlington: Elsevier Science, pp.249-253.

8.      Beentje, H. and Williamson, J. (2016). The Kew plant glossary. 2nd ed.

9.      Halliday, G. (2019). A Flora of the East Greenland Central Fjord region 70°N-77°N. Trollius Publications 2019, p.220.

10.  REINHAMMAR, L. (1999). Allozyme differentiation between the lowland Carex capitata and the alpine Carex arctogena (Cyperaceae) in Scandinavia. Biological Journal of the Linnean Society, 67(3), pp.377-389.

11.  Carex arctogena Harry Sm. in GBIF Secretariat (2019). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2019-10-11.

12.  Ipni.org. (2019). International Plant Names Index. [online] Available at: https://www.ipni.org/n/45766-2 [Accessed 11 Oct. 2019].

13.  Robertson, A. (1979). HISTORY OF THE CLASSIFICATION OF THE GENUS CAREX. TAXON, 28(5-6), pp.535-548.

14.  Villaverde, T., Escudero, M., Martín-Bravo, S., Jiménez-Mejías, P., Sanmartín, I., Vargas, P. and Luceño, M. (2017). Bipolar distributions in vascular plants: A review. American Journal of Botany, 104(11), pp.1680-1694.

15.  Graven, P., de Kroster, C.G., Boon, J.J. & Bouman, F. (1996) Structure and macromolecular composition of the seed coat of the Musaceae. Annals of Botany, 77, 105–122

16.  Hyam, R. and Pankhurst, R. (1995). Plants and their names. Oxford [England]: Oxford University Press, p.90.