Graminoid forb growing in extensive mats due to slender (1—1.5 mm), whitish rhizomes, typically with branches of 2—6(8) cm between aerial shoots. Rhizome branches rooting at nodes (at base of aerial shoots and between these), but not to the same degree as in Arctophila. Aerial shoots ascending from rhizome, at base with several prophylls (reduced leaves without or only with a short blade). Culms 10—20(30) cm, erect, smooth and glabrous. Base of culms with some withered leaf remains but no distinct sheaths. Most stands observed with an abundance of flowering shoots (when not over-grazed by geese) but this plant is difficult to discover if the stands have no culms.

Sexual reproduction unproven; efficient local vegetative reproduction by clonal growth by rhizomes. This hybrid species, considered to have originated from parents from two different genera, has been assumed seed-sterile and propagating by clonal growth alone. The type specimen from Malozemelskaya Tundra in NE European Russia seems to be pollen and seed sterile (specimen in LE, the Komarov Herbarium in St. Petersburg, studied by us). One of the three known populations or population groups in Svalbard also seems to have pollen sterile plants (Grønfjorden), whereas the plants of the Forlandet population may have functional anthers and pollen and those of the Kongsfjorden populations have a better production of anthers and pollen than normally seen in Svalbard in both its assumed parental species (Arctophila fulva and Dupontia fisheri). The distribution pattern also supports that at least the Kongsfjorden population reproduces by seed. Whereas only single stands have been found at Grønfjorden and at Fuglehuken on Forlandet, at least seven separate stands have been found at Kongsfjorden reaching from the settlement of Ny-Ålesund in the southeast to Stuphallet in the northwest. See Comments for further speculations.

Dispersal is probably mainly by rhizome fragments spread to new sites by birds. Whether seeds are produced (and spread) is not known.

Arctodupontia is closely related to both Arctophila and Dupontia and assumed to be a genus hybrid. It is sometimes difficult to keep apart from both these genera (and the Kongsfjorden plants have previously been misidentified as both these genera). Arctodupontia and Dupontia do not have the coarse, strongly distichous leafy shoots of Arctophila and never leaves as broad as those of Arctophila (4—9 mm); however, there are narrow-leaved Arctophila plants, too. The glumes and lemmas of Dupontia are much longer than those of Arctophila and Arctodupontia, with extended, deeply fringed tips.

The open panicle of Arctodupontia may resemble that of some Poa species but the leaves are markedly different (not keeled and in more or less distichous arrangement in Arctodupontia, distinctly keeled and never in distinct distichous arrangement in Poa except for P. alpina), and also the keeled backs of glumes and lemmas in Poa contrast with the rounded backs in Arctodupontia.

Arctodupontia scleroclada is confined to marshes and mires but not submerged in ponds as Arctophila fulva usually grows.It is rather found in wet moss tundra, sometimes as the only vascular species in the moss mats, and in mossy mires. It seems to be indifferent as to soil reaction (pH) but has only been found in areas with circumneutral or basic substrates. Its main population in Svalbard, and the only one of possibly evolutionary importance, is the one along the southwestern shore of Kongsfjorden.

Within Svalbard, Arctodupontia scleroclada is found in three areas: one site at Grønfjorden in W Nordenskiöld Land, discovered by K.I. Flatberg; one site at Fuglehuken northernmost on Prins Karls Forland, discovered by R. Elven and I.G. Alsos in 2009; and a group of occurrences along 3—5 km on the southwestern shore of Kongsfjorden from the settlement of Ny-Ålesund to Stuphallet (Oscar II Land), known from the early parts of the 20th century but misidentified until after 2000.

Except for the type locality in Malozemeleskaya Tundra, these are the only sites reported from Europe; some additional localities are reported from Siberia, the Russian Far East, and NE Canada. Specimens (LE) supporting occurrence in Chukotka (the Russian Far East) were based on Arctophila fulva (R. Elven observ.). However, N.N. Tzvelev and B.A. Yurtsev stated (in Elven et al. 2011) that there are more specimens and occurrences. Darbyshire & Cayouette (2007) reported this hybrid from Mansfield Island in the Hudson Bay, Canada, with indehiscent anthers.

The following note is copied from Elven et al. (2011) and is 'signed' by A.K. Brysting, K.I. Flatberg, I.G. Alsos, and R. Elven: "Arctodupontia scleroclada was fairly recently documented from Svalbard (Brysting & Elven 2005) where it now is known with populations in three restricted areas, more or less in the absence of at least one of its presumed parents. In the Ny-Ålesund area (Brysting and Elven), the Dupontia parent seems to be of the "fisheri" morph, i.e., probably octoploid, and here is found dehiscent anthers and well-formed pollen. Dupontia itself is not documented from within the range of Arctodupontia in this area. In the Grønfjorden area (Flatberg), the assumed Dupontia parent is of the "psilosantha" morph, i.e., probably tetraploid. In Prins Karls Forland (Alsos and Elven in 2009), the parental combination is uncertain but the plant is found together with Dupontia of the "psilosantha" morph, occurs in a vast population, and has dehiscent anthers. Inflorescences were collected in the Ny-Ålesund area in September 2009 but were still in a late anthesis stage, without developed fruits. The type collection of Poa scleroclada from northeastern Russia represents this hybrid but is morphologically different from all three Svalbard populations. We provisionally apply the name Arctodupontia scleroclada for the collective assumed hybrid irrespective of which part of D. fisheri that partakes."

It is a paradox that the Kongsfjorden population of Arctodupontia scleroclada seems to be much more efficiently reproductive in Svalbard, at least concerning pollen development, than both its assumed parents. Anne Brysting counted the chromosome number 2n = 42 (hexaploid) in a stand within Ny-Ålesund in 2000. As Arctophila fulva is known throughout with 2n = 42, whereas the two main numbers in Dupontia are 2n = ca. 44 (the 'psilosantha' morph) and 2n = ca. 88 (the 'fisheri' morph), this number is strange. We may have to re-evaluate the entire group as to what are species and genera. See Dupontia for further discussion and Brysting & Elven (2005) for a more detailed study of the Kongsfjorden plant.

It is probable that this hybrid crops up here and there in the Arctic where its parents meet (and they often meet), but until now the only place where such hybridization seems to have resulted in a new and possibly reproducing species, is the Ny-Ålesund area. Here, the fate of this extremely rare species, where Norway has the only known possibly reproducing population in the world, is endangered by the Norwegian government's focus on management of birds (barnacle goose) and reindeer (introduced in the area), rather than plants. The legal protection of the barnacle goose, combined with the experimental re-introduction of reindeer to Brøggerhalvøya, has led to a huge increase in grazing pressure. Such grazing first removes all culms and possibilities of seed reproduction, thereafter the vegetative shoots and the entire biomass of the plants. Of the 7 known stands of A. scleroclada at Kongsfjorden, 6 are located in and around the settlement of Ny-Ålesund where the species was abundant until the 1980ies. Now, less than 10 flowering shoots were found during a survey in 2009, all of them within a goose exclosure. The only stand in the Kongsfjord area which has not been checked in recent years, and which may be intact, is found at Stuphallet, some kilometres northwest of the settlement. It was last collected at Stuphallet area in 1975.

In a recent study (Tkach et al. 2020) Arctophila is merged within Dupontia as D. fulva Röser & Tkach. If this approach is followed, also Arctodupontia with A. scleroclada must be included, as Dupontia scleroclada (Rupr.) Rupr.

Brysting, A.K. & Elven, R. 2005. Tundragras Dupontia fisheri rundt Ny-Ålesund, Svalbard. – Blyttia 63: 186–193.

Darbyshire, S.J. & Cayouette, J. 2007. XArctodupontia Tzvelev. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 24. Magnoliophyta: Commelinidae (in part): Poaceae, part 1: 604–605.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Tkach, N., Schneider, J., Döring, E., Wölk, A., Hochbach, A., Nisen, J., Winterfeld, G., Meyer, S., Gabriel, J., Hoffmann, M.H. & Röser, M. 2020. Phylogenetic lineages and the role of hybridization as driving force of evolution in grass supertribe Poodae. – Taxon 69: 234–277.