Mat-forming herb with extensively branched, thin, white rhizomes and also above-ground stolons, with branches up to 10 cm long. Most leaves basal. Flowering stems ascending to erect, mostly 1–3(5) cm tall but occasionally to 15(20) cm in fertilized sites, usually with 1–2 leaves, the uppermost attached near or above the middle of the stem, and several leaf-like bracts in the inflorescence. The entire plant is glabrous and green or yellowish green.
Leaves alternate. Basal leaves on petioles up to 3 cm (or more), blades more or less orbicular or reniform in outline, 4–10 × 4–15 mm, with 5(7) broad, very shallowly incised lobes, apically rounded or nearly truncate. Stem leaves similar but usually smaller and with shorter petioles.
Inflorescence a dense or more open, bracteate cyme up to 1.5 × 3 cm. Bracts numerous, similar to basal leaves but with short petioles and blades with a cuneate base, usually 3–5-lobed, supporting branches and clusters of flowers in the inflorescence, functioning more or less as a broad perianth (in the absence of petals).
Flowers radially symmetric, ca. 3 mm broad, with 4 free sepals but no petals. Sepals 0.7–1.0 × 1.0–1.3 mm, very broadly ovate or triangular, obtuse, green. Stamens ca. 4 (the name ‘tetrandrum’ means ‘with four stamens’), minute, in the margin of a disc surrounding the gynoecium; filaments ca. 0.2 mm; anthers ca. 0.2 mm. Gynoecium of 2 carpels, fused in the lower part, with 2 free styles.
Fruit a 2-roomed capsule with several seeds. Capsule opening at the top with two valves into a shallow cup. Seeds glossy brown, ca. 0.8 × 0.5 mm.
Sexual reproduction by seeds; local vegetative reproduction by rhizomes and fragmentation of clones. The flowers may be adapted to some insect pollination (disc) but are probably mainly pollinated by water (a ‘splash-cup’ mechanism, see below). Seed set is fairly regular in Svalbard. Seeds germinate to 25 % in an experiment (Alsos et al. 2013).
Seed dispersal in Chrysosplenium is reported to be mainly by water through the ‘splash-cup’ mechanisms where rain drops fall into the broad cups and splash the seeds a few centimetres away. Farther distribution may take place by surface water, probably also by birds for much longer distances.
There is nothing similar in Svalbard.
Growing in moist to wet moss mats and mossy meadows, almost always in a dense vegetation where leaves and stems are found on a moss carpet surface. The species is probably confined to quite fine-grained substrates but is largely indifferent as to soil reaction (pH).
Middle and northern arctic tundra zones and weakly continental to weakly oceanic sections. Chrysosplenium tetrandrum is found on Bjørnøya (fairly rare, 5 stations reported by Engelskjøn & Schweitzer 1970) and on Spitsbergen, there throughout the western and central parts from Sørkapp Land in the south to the north coast in Albert I and Haakon VII Lands.
The global range is circumpolar, also reaching some distance south, in Europe to N Fennoscandia, in North America to the central Rocky Mountains.
Chrysosplenium tetrandrum belongs to a species group, the C. alternifolium group, where the delimitation between entities is rather unclear (see Elven et al. 2011). In Europe, there are two well demarcated taxa, the octoploid (2n = 48), temperate to boreal C. alternifolium L. with 8 stamens, and the tetraploid (2n = 24), arctic C. tetrandrum with 4 stamens. No intermediate forms or intermediate ploidy levels have ever been reported from this region. The problems are found elsewhere. In North America, Packer (1963) reported the 16-ploid (2n = 96) C. rosendahlii Packer with 4–8 stamens. In Siberia, C. alternifolium s. str. is absent but replaced by the mainly octoploid ssp. sibiricum (Ser. ex DC.) Hultén and the 11–12-ploid (2n = 66, 72) ssp. arctomontanum V.V.Petrovsky (see Tolmachev & Martinenko 1976; Petrovsky in Zhukova & Petrovsky 1980; Taraskina 1984; Hultén & Fries 1986; Malyschev 1994).
Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.
Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/
Engelskjøn, T. & Schweitzer, H.J. 1970. Studies on the flora of Bear Island (Bjørnøya). I. Vascular plants. – Astarte 3: 1–36.
Hultén, E. & Fries, M. 1986. Atlas of North European vascular plants north of the Tropic of Cancer. I–III. – Cramer, Vaduz.