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Elatine L. Ill.
Linnaeus, Sp. pl.: 367 (1753).
Literature. Uotila 1974.
Probably therophytes (summer-annuals). Aquatic or amphibious, glabrous herbs. Stem prostrate or erect, branched, rooting at nodes, terete, soft, with central vein and thick aerenchyma with large air canals, whitish when buried in the soil, greenish in water and often tinged with red when aerial; roots without main branches, thin, whitish to brownish, a few to numerous at a node. Leaves opposite or whorled, simple, petiolate or sessile, with small interpetiolar stipules; blade linear, oblong, elliptic, lanceolate, ovate or obovate, apex often slightly notched; margin entire to obscurely and remotely crenate because of the hydatodes at the ends of the veins; stipules caducous, membranous, entire or with some teeth or lobes.
Flowers single in leaf axils, sessile or pedicellate, tiny, cleistogamous when submerged or ± chasmogamous when aerial, 3- or 4-merous. Sepals 2-4, ± persistent, with 1 vein ending to a hydatode. Petals 3 or 4, membranous, disappearing before sepals, in submerged flowers whitish, enclosing stamens and carpels, in aerial flowers mostly pink, campanulately spreading. Stamens as many as or twice as many as petals, 3 (opposite to sepals), 6 or 8 (opposite to sepals and petals), shorter than petals; filament wider at base, narrowing upwards; anther globose. Carpels 3 or 4¸ ovary 3- or 4-celled, placentation axile, stigmas capitate. Fruit a subglobose to turnip-shaped to almost cylindrical, thin-walled, ± septifragal capsule, divided into 3 or 4 rooms, seeds more or less visible within. Seeds numerous, cylindrical, almost straight to bent or asymmetrically horseshoe-shaped, one end rounded and the other truncate; surface with reticulate pattern from 9-10 rows of transversally elongated pits.
Chromosome base number x=9. Polyploidy; tetraploids, octoploids and duodecaploids in Norden. - Small chromosomes, difficult to count, therefore few counts; reports of 2n=40 probably refer to 2n=36.
Biology. All Elatine taxa have adapted themselves well to fluctuating water level and temporary drying-out of the habitats. In all species, the size and density of populations can vary considerably between years, especially depending on the water level. The seeds appear to stay viable for many years. Elatine seeds probably spread easily with birds, and temporary occurrences are to be expected.
E. hexandra, Elatine hydropiper, E. orthosperma and E. triandra often grow 2 or 3 species together in mixed colonies, and in the vegetative state they may be difficult or sometimes even impossible to distinguish from each other, especially when growing terrestrially. From the end of July onwards they usually flower and fruit abundantly, and determination is safe if a hand-lens or binocular is used.
They are sometimes mistaken for small Callitriche palustris, Crassula aquatica, Lythrum portula, Montia arvensis or Limosella aquatica, which grow in similar habitats, but the Elatine species have opposite leaves with stipules and hydatodes, whereas the others have opposite or basal leaves without stipules and hydatodes; there are also clear differences in leaf shapes and floral and fruit characters, visible at least with a hand-lens.
Leaf measures refer to grown-up leaves; young leaves of species 2-5 have relatively shorter petioles and rounder blades. Stipules are present on young leaves. Sepals, petals and stames are thin and fragile, often difficult to study on herbarium specimens and especially in cleistogamous flowers. It seems that in cleistagamous flowers petals may also be absent.
Linnaeus, Sp. pl.: 368 (1753). - Type: Linnaean Herbarium Stockholm 161.5 (S) lectotype, selected by Jonsell & Jarvis, Nordic J. Bot. 22: 82 (2002).
D Krans-Bækarve. F isovesirikko. N kransevjeblom. S kransslamkrypa.
Upright amphibian herb, (2-)5-30(-40) cm (terrestrial plants 2-10 cm), green. Stem erect or ascending, mostly simple (sometimes with few, similar-sized branches in lower half, but without secondary branches), 2-7 mm thick (in terrestrial plants 0.8-1.2 mm); aerial internodes (3-)7-10 mm, submerged internodes 10-40 mm; adventitious roots numerous at lower nodes, also at nodes with submerged leaves and sometimes at the lowermost aerial nodes. Leaves in whorls, sessile, green, usually di- to trimorphic with lower (submerged) leaves, upper (aerial) leaves and some intermediate whorls (sometimes all leaves submerged; in terrestrial plants all leaves ± intermediate); stipules narrowly triangular, 1-1.5 mm, with filiform apex and few teeth. Submerged leaves in whorls of (4-)8-17, flaccid; blade linear, 10-30(-45) x 0.4-1(-1.5) mm, with 1 branchless main vein ending in a distinct brown hydatode at the retuse apex. Aerial leaves in whorls of 3, stiff, patent; blade ovate to elliptic, 7-16(-23) x 4-9(-10) mm; base slightly cordate to rounded; main veins 5-12, ± parallel, branched; the hydatode at apex distinct, the others mostly small, brownish, up to 12 along each side. Intermediate leaves in whorls of 4-8, stiff; blade 5-8 x 2-3.2 mm (in small terrestrial plants 0.7-0.4 x 2.5-0.8 mm); main veins (1-)3(-5); a distinct hydatode often only present at the leaf apex.
Flowers in axils of aerial and intermediate leaves, usually 3 at a node (but terrestrial plants have mostly only 1 flower per node), sessile or sometimes short-stalked (pedicel to 1.7 mm). Sepals 4, connate up to 1/3-1/2, all alike, triangular-ovate, 1-1.2 x 1-1.2 mm, ± green with baseward widening membranous borders; margin entire. Petals 4, broadly elliptic, 1.6 x 1.0 mm. Stamens 8. Carpels 4. Capsule subglobose, 2.2-2.8 x 3.0-4.1 mm, depressed at the apex, mostly first opening along the thinner hyaline septa. Seeds irregularly arranged, 120-160(-200), cylindrical, almost straight to slightly bent, 0.70-0.80 x 0.23-0.28 mm, pale greenish brown; pits conspicuous, 15-21 in each row, 0.02-0.03 x 0.05-0.06 mm. - Mid-summer to late summer.
Distribution. Nem--BNem. - The present Nordic area (in F) is quite isolated from the southern main area. All localities are in places completely changed by man, and the species is regarded as archaeophytic, although apparently not brought in by man but by birds. Declined during last decades, most finds old. F scattered and locally fairly frequent in a fairly sharply limited area in the southwest, from mainland V (also a few finds in the archipelago near Turku) to U Elimäki, to southern St and southern EH; one find from PH Virrat 1887, and an uncertain find from ES Taipalsaari 1934 (a pupil’s specimen); after 1980 known from V (several localities), U (Helsinki, Myrskylä), St (Alastaro, Loimaa, Oripää) and EH (Nokia, Pirkkala, Somero, Tampere). N Te Kragerø 1881-1888, probably introduced with hay from Germany; a specimen from Ak Ås 1902 probably mislabelled. D Sjæ, Frederiksberg, before 1830, interpreted as indigenous, disappeared (Larsen & Pedersen 1960: 61). - Uncertain old specimens without locality known from S.
Continental Europe to Anatolia, Caucasus and western Siberia, from the Mediterranean north to Northern Germany, Denmark and Poland, with an outpost in Finland; coastal N Africa; rare everywhere and mostly declined.
Habitat. In full sun, on clay or clayey soil (seldom on mud or gravel), without competition from other plants. Often in water down to 50 cm (thriving best in 10-30 cm deep, more or less standing water), sometimes on land (on wet bare soil). Permanently or temporarily water-filled depressions in arable fields and pastures (e.g. ditches, clay-pits, pools and tracks); also recorded from roadside ditches, old fish-ponds, sheltered lake coves and brook-banks, wet paths in woodland, abandoned gravel pits, brick clay fields and stone quarries. Due to changes in the rural landscape, the frequency of suitable habitats decreased strongly in the latter half of the 20th century.
Biology. In more southern areas Elatine alsinastrum can be perennial or at least winter-annual. However, there is no evidence that it can survive winter as adult or seedling in Finland, and most or all of its habitats will be frozen during the winter.
Flowers are self-pollinated even when aerial and opened. Pollen derives from the stamens opposite to the sepals, usually the filament grows so that the anther touches the stigma. Number of flowers in a well-grown plant is high, and a great proportion of the flowers produce fruits and seeds. In a population in U Helsinki the seed production was estimated to be at least 21 000 seeds/m² (Kurtto 1987).
Seeds can germinate immediately when shed, but most seeds germinate next summer or later. In clayey soil seeds can survive in seed bank for many decades and germinate again when the soil is dug. Germination seems to need much light. Colonies vary much in size between years, and most sites remain suitable for E. alsinastrum only for a few years.
Taxonomy. Elatine alsinastrum forms a monotypic group (sect. Pitymopitys) in the genus Elatine, characterized by erect stem and whorled leaves.
Similar taxa. Submerged Elatine alsinastrum resembles submerged Hippuris vulgaris; H. vulgaris has a creeping horizontal rhizome with erect branches and its leaves have a tapering, ± acute apex, while there is no rhizome in E. alsinastrum and its stems and braches are erect to ascending, and the submerged leaves are linear, with a retuse apex.
De Candolle, Icon. Pl. Gall. Rar.: 14 (1808). - Tillaea hexandra Lapierre, Journ. Phys. 56: 358 (1802). - Described from France.
Literature. Salisbury 1967.
D Sekshannet Bækarve. F kuusihedevesirikko. N skaftevjeblom. S skaftslamkrypa.
Aquatic plants forming 2-10(-15) cm wide green patches; terrestrial plants much smaller, often dark red or violet. Stem prostrate, with simple branches, rooted at nodes except for the apicalmost parts, which can be ascending to erect, 1-5 cm; mature internodes 1-10 x 0.5-1.0 mm; adventitious roots 2-6 at a node. Leaves opposite, (2-)2.5-11(-14) mm, patent to erectopatent, in prostrate parts horizontal to obliquely upright; petiole often very gradually widening to the blade, 1-5 mm, ratio petiole/blade length c. (0.3-)0.8-1.3(-2); blade elliptic to elliptic-oblong to obovate, (1-)2-6(-8) x (0.5-)1.0-1.5(-3) mm; base long-attenuate; apex obtuse to rounded, sometimes slightly notched; veins pinnate; the hydatode at apex usually blackish and fairly distinct, the others mostly fairly indistinct; stipules narrowly triangular to linear, to 0.8 mm, long-acuminate, with a few teeth.
Flowers single at the nodes, stalked (pedicel at fruit stage (0.5-)3-10(-14) mm). Sepals 3, connate up to 1/3, usually dimorphic (2 large ones, 1.0-2.4 x 0.7-2.0 mm, and one up to 1/3 smaller), roundish to broadly ovate, pale green (in aerial flowers usually dark green or red, apically spreading); margin entire. Petals 3, roundish, 1.2-1.5 mm. Stamens 6. Carpels 3, exceptionally 4. Capsule subglobose to globose, somewhat depressed at the apex, (1-)1.2-1.5(-1.7) x 1-1.2 mm; walls irregularly broken when opening. Seeds irregularly arranged, 15-50(-60), cylindrical, slightly bent in the apical half or at the middle, sometimes clearly narrowing at apex, 0.6-0.7 x 0.24-0.26 mm, pale brownish to blackish; pits conspicuous, 18-25 in each row, 0.02-0.03 x 0.04-0.05 mm. - Mid-summer to late summer.
Distribution. Nem-BNem. - D NJy extant at Vangså, Svankær and Torup, until 1969 also known from Råbjerg Mile and Førby Sø; VJy 8 localities along the coast, extant at least in Dalgas Plantage and Skånsø; ØJy 8 localities in the Silkeborg-Bryrup region (probably extant in one or more lakes in Grane Plantage), previously also recorded from Randbøl Hede c. 1885; SJy Hjerpsted 1887, Vedsted (2 localities) latest 1973. N along the coast in Øf, Vf (Sandefjord 1896), AA (Arendal, Risør, Tvedestrand), VA, Ro (north to Stavanger), Ho and SF; He Stange 1981, Ringsaker 1981. S common in southern Vrm, fairly rare on the west coast in BhG, Hl, Vg, in southwestern SmI (at least temporarily increased), Dls and Nrk (Kvistbro, Ölsboda, Nysund); Bl Lösen 1897, ÖG Motala 1879, Srm Gryt 1970, 1971, Vsm Arboga 1864.
Western and central Europe (north to Scotland and southwestern Norway, south to the Iberian Peninsula) and Morocco.
Habitat. On clayey, fine sand to sand or sometimes gravel bottom with some gyttja in shallow water (usually above 50 cm depth, rarely down to 3 m) or at shoreline. Oligotrophic to slightly eutrophic lakes with acid or circumneutral water, sometimes near sea in the mouths of rivers and brooks, but probably not in real brackish water. Possibly favoured by certain lake regulation regimes (Edqvist & Karlsson 2007).
Biology. When growing on wet soil Elatine hexandra usually flowers abundantly, the flowers are chasmogamous and the seed production is high. In submerged conditions the flowers are cleistogamous and have a lower seed production than the chasmogamous flowers. Seed production in late flowers is lower than in earlier ones, sometimes only a few seeds per capsule. Seeds spread with rain water, running water and on feet and feathers of birds (Salisbury1967).
Similar taxa. Elatine hexandra, especially small terrestrial plants with short-pedicellate leaves, can be difficult to distinguish from E. triandra (3), since their seeds are fairly similar and the flowers of E. hexandra may have a pedicel shorter than 0.5 mm. However, the seeds of E. hexandra are somewhat larger, more narrowing to the apex, somewhat comma-shaped (those of E. triandra are more cylindric, bent at the middle), and E. hexandra has larger sepals and more (6) stamens. In general, specimens of E. hexandra are more often correctly determined than those of the three similar species.
Schkuhr, Bot. Handb. 1: 345 (1791). - Described from Germany.
Elatine callitrichoides (Nyl.) Kauffm. (1866). - Elatine triandra var. callitrichoides Nyl. (1851).
D . F kolmihedevesirikko. N trefelt evjeblom. S tretalig slamkrypa.
Aquatic plants forming 4-15(-20) cm wide dark-green patches; terrestrial plants smaller, often red. Stem prostrate, often richly branched and with many secondary branches (sometimes only with a few simple branches), rooted at nodes and often buried in the soft bottom sediment except for the apicalmost parts, which can be ascending to erect, 1-5(-10) cm; mature internodes 5-18(-30) x 1.2-1.8 mm; adventitious roots 2-6 at a node. Leaves opposite, 6-20(-21) mm, patent, in prostrate parts of the shoot mostly horizontal on the bottom; petiole 0.5-3 mm, ratio petiole/blade length up to c. 0.25-0.5(-1); blade lanceolate-linear to narrowly lanceolate to oblong, 5-18(-20) x (1.5-)2-2.6(-3.3) mm; base rapidly widening from the petiole; apex usually distinctly notched; veins pinnate; hydatodes mostly distinct, dark brown; stipules triangular, 0.6-1.3 mm, with small teeth.
Flowers single at the nodes (or sometimes in both leaf axils), sessile or rarely very shortly stalked (pedicel at fruit stage to 0.3 mm). Sepals 2-3, slightly connate at base, dimorphic (2 uniform and 1 smaller or rudimentary); the longer ones c. 0.5 mm, elliptic, green, margin entire. Petals 3 (sometimes 0), broadly elliptic-ovate, ca. 1 x 0.7 mm. Stamens 3. Carpels 3 (rarely 2). Capsule subglobose, somewhat depressed at apex, 1.2-1.4 x 1.4-1.7 mm; walls irregularly broken when opening. Seeds irregularly arranged, (3--)35-50, cylindrical, bent near the middle, 0.5-0.6 x 0.15-0.2 mm, greenish to yellowish brown; pits conspicuous, 20-24 in each row, 0.015-0.025 x 0.035-0.045 mm. - Mid-summer to late summer.
[2n = 40]
Distribution. BNem-MBor. Alt. N He and F PeP ca. 150 m. - N fairly common in lowland areas of Ak, He and Øf; Vf Larvik 2002, Bu Drammen 1921, Lier 1945, 1959, Övre Eiker 1948, Ringerike 1933, AA Tvedestrand 1937. S common in Vrm and Nb, fairly rare in BhG, Vg, Nrk, Srm, Vsm, Upl, Dlr, Ång, Vb; Sk Ängelholm 1888, Kristianstad 1984, 1985, Ven 1811, Bl Karlskrona 1891-1937, Ronneby 1935, Nättraby 1820-1885, Lyckeby 1855-1868, Klm Vissefjärda 1926, Fliseryd 1941, Ukna 1941, 1981, SmI first record Väckelsång 1921 (recent finds from at least five areas), Hl Ås 1910, Dagsås 1989, Falkenberg 1890, 1911, Halmstad 1873, Laholm 1926-1947, Dls Åmål 1903, Frändefors 1925, Valbo-Ryr 1925, Ög Linköping 1883, Ringarum 1941, Gst Gävle 1843-1887, Kille 1877, Ockelbo, Hls, Mpd Selånger 1824-1952; in many provinces most finds are old. F common in mainland Finland from V to Kn, OP and PeP.
Widespread but rare in central Europe, France, Spain, the Balkan peninsula, central Russia; more common in Norden and the adjacent Russian Karelia. Reported also from Siberia, East Asia, N America and S Africa, but at least some of the records probably represent other taxa.
Habitat. Mostly in shallow water (to 30 cm depth, sometimes to 150 cm), seldom on wet ground above shoreline. On bare soil or among sparse taller vegetation on soft silty and oozy gyttja (less frequently on clay, sand or gravel). Mesotrophic to eutrophic lakes, rivers, ponds and somewhat brackish water. Often in man-influenced sites such as grazed shores and boat harbours. A weak competitor, declined due to loss of open habitats and heavy eutrophication of waters.
Biology. Even though there are sometimes flowers in both leaf axils at a node, usually only one flower develops fully and produces seeds. Number of seeds per capsule varies much; small late capsules may have less than 5 seeds. Chamogamous flowers seem to be less frequent than in other Elatine taxa; field studies would be needed to know whether the only reason is that Elatine triandra grows less often above water line.
Variation. Leaves vary much in size and shape. Tall plants with long internodes and long narrow, lanceolate-oblong, flaccid leaves, with apical parts of the shoot and branches not rooted but upright, and often with flowers in both leaf axils of a node, have been distinguished as E. callitrichoides. Such plants often grow in sheltered places on very soft oozy bottoms; they are modifications and do not deserve taxonomic recognition.
Similar taxa. Every now and then Elatine triandra is mixed up with other small Elatine species, but it differs from them in flowers, fruits and seeds. Even without flowers it is usually distinguishable from the other Elatine species by the shorter petiole and the usually linear-lanceolate to lanceolate blade with ± truncate apex and distinct dark hydatodes; other species have longer petiole and ovate to obovate blade with more rounded apex and often more obscure hydatodes.
In the field, E. triandra can often be spotted at a glance: most leaves of prostrate stem portions lie more or less flat on the bottom (in E. hydropiper and E. orthosperma the horizontal blades are raised on more or less erect petioles, in E. hexandra leaves are spreading from horizontal to obliquely upright).
Linnaeus, Sp. pl.: 367 (1753). - Type: 517.2 (LINN) lectotype, selected by Jonsell & Jarvis, Nordic J. Bot. 22: 82 (2002).
E. hydropiper var. gyrosperma Düben ex Lange (1850). - Elatine gyrosperma (Düben ex Lange) Meinsh. (1878). - E. hydropiper subsp. gyrosperma (Düben ex Lange) P. Fourn. (1936).
Elatine spathulata Gorski (1830).
D Vandpeber-Bækarve. F katkeravesirikko. N krossevjeblom. S slamkrypa.
Aquatic plants forming up to 12(-18) cm wide green patches; terrestrial plants smaller, often red. Stem mostly prostrate, usually only with simple branches, rooted at nodes and often buried in the soft bottom sediment except for the apicalmost part, which is often ascending to erect, 1-3(-5) cm; mature internodes (1-)3-15 x 0.5-1 mm; adventitious roots 2-8 at a node. Leaves opposite, to 15(-20) mm; in erect parts of the shoot leaves are erectopatent, in prostrate parts petioles are mostly erect but leaf-blades often horizontal; petiole gradually widening to the blade, (1-)3-6(-15) mm, ratio petiole/blade length in grown-up aquatic leaves c. (0.8-)1.1-2, in terrestrial plants and in young shoots c. (0.8-)1; blade ovate to elliptic to obovate, (1-)2.5-6(-7) x (0.4-)1.5-3.4 mm; base long-attenuate; apex obtuse to rounded, sometimes slightly notched; veins pinnate; hydatodes mostly obscure; stipules narrowly triangular, 0.7-0.8 x 0.25-0.4 mm, usually with lobelike, long, narrow teeth and long acute apex.
Flowers single at the nodes, sessile or sometimes very shortly stalked (pedicel at fruit stage to 0.3(-1.2) mm). Sepals 4, slightly connate at base, all alike, elliptic, 0.5-1 x 0.5 mm, green; margin sometimes with a pair of small teeth on each side. Petals 4, elliptic, 1-1.3 x 1-1.1 mm. Stamens 8. Carpels 4. Capsule ± turnip-shaped (depressedly globose), 1-1.6 x 1.5 mm; walls mostly irregularly broken when opening. Seeds fairly regularly radially arranged, 12-30, cylindrical, 0.17-0.19 mm thick, hooked to asymmetrically horseshoe-shaped, the longer arm 0.54-0.58 mm and the shorter arm 0.37-0.43 mm (at least 2/3 the length of the longer one, usually curved inwards), pale brown or pale greenish to pale yellowish brown; pits inconspicuous, 50-60 in each row; 0.01-0.025 x 0.03-0.035 mm. - Mid-summer to late summer.
Distribution. Nem-NBor. Alt. S TL 346 m. - D VJy extant at Nees (3 localities), Filsø, Søvig Sund and Guldager, previously also at Sønder Felding 1955 and Ribe 1870-1892; Sjæ latest Damhus Sø 1934 and Birkerød 1892, considerably older finds are known from c. 5 additional localities in the eastern part of the province (Gröntved 1956). N fairly common in Øf, southern part of Ak and Bu; rare in coastal Vf (Larvik 1886, 1902, Borre 1970, Svelvik 1913, Tjøme 1884), Te (Bamble 1990, Porsgrunn 1888, Skien 1887, Solum 1969), AA (Arendal 1894, Tvedestrand 1937), VA (Kristiansand 1881-1999, Mandal 1881-1965); He Hamar 1983, 1984, OP Østre Toten 1981, Ro Hå 1992, 1999, NT Namdalseid 1930, Øverhalla 1927, ØFi Sør-Varanger 1993; reported from Tr Senja 1977 (Spjelkavik 1979), but no specimen seen. S fairly common in BhG, Vg, Ög, Vrm, Nrk, Srm, Upl, Vsm, Dlr, Vb and Nb, fairly rare in Sk, Bl (Karlshamn 1883, Lyckeby 1855-1902, Nättraby 1888, Sölvesborg 1879), Hl, SmI (c. 20 lakes and ponds), Dls, Hls, Ång, Klm (recent localities in the north); Gst Gävle 1837-1955, Torsåker 1926, Mpd Sundsvall, LL Gällivare, Kiruna and TL Jukkasjärvi, Karesuando. F fairly common in most of mainland Finland up to PeP; rare and partly absent from the archipelago in the south, fairly common along the Gulf of Bothnia north of EP Vaasa archipelago; a few finds in Ks, KiL, InL; from A uncertain reports from the first half of the 19th century (see Cedercreutz 1947; no specimen seen and not found later) - Late-Glacial fossil finds (seeds) from SF Vågsöy (Birks 2000).
Europe except the most oceanic and the northernmost parts, also largely absent or rare in the Mediterranean; few finds from Siberia and East Asia.
Habitat. In shallow water (mostly to c. 50 cm depth, seldom down to 3 m), rarely on wet ground above shoreline. On bare soil or among sparse taller vegetation on clay, silt, sand or gyttja, sometimes on gravel or mud. Meso-eutrophic lakes, rivers and slightly brackish water (often in man-influenced sites like grazed shores and boat harbours); sometimes also in ponds, pools and ditches. A weak competitor, declining due to loss of open habitats and heavy eutrophication of waters.
Biology. According to Luther (1951), cleistogamous submerged flowers produce seeds much earlier than chasmogamous flowers at shoreline. Seeds do not float but sink immediately (Ravn 1894). - Spreading easily with drifting shoot fragments (Luther 1951).
Taxonomy see E. orthosperma.
Similar taxa. Elatine hydropiper is vegetatively very similar to E. orthosperma (5), but they differ in the shape of capsule and seed (see key); the differences can be seen already in developing fruits. Plants without mature flowers or fruits cannot be determined with certainty. However, E. hydropiper has usually ± sessile flowers (E. orthosperma flowers are usually short-stalked) and slightly larger leaves, which are relatively wider and mostly ovate to elliptic (leaves of E. orthosperma are elliptic to obovate). Although frequently occurring in mixed colonies E. hydropiper and E. orthospema have also slightly different habitat preferences: E. hydropiper grows in deeper water, less often above waterline, and is more tolerant than E. orthosperma to soft bottom, slighty brackish water and eutrophication. - Compared with E. hexandra (2), E. hydropiper has leaves with longer petioles, and generally the blade is wider and rounder.
Düben, Bot. Not. 1: 88 (1839). - E. hydropiper var. orthosperma (Düben) Hartm. (1843). - Elatine hydropiper subsp. orthosperma (Düben) Hartm. (1849). - Type: S BhG, Gothoburgi, Göta elf, sept 1839 M.W. von Düben (Fries, Herbarium Normale Fasc. 6, No. 29. 1839) (UPS) lectotype, sel. by Uotila, Ann. Bot. Fennici 44: **** (2007).
Literature. Odland 2001.
D . F oikovesirikko. N nordleg evjeblom. S nordslamkrypa.
Aquatic plants forming up to 10 cm wide green patches; terrestrial plants smaller, red. Stem mostly prostrate, usually only with simple branches, rooted at every node and often buried in the bottom except for the apicalmost parts, which can be ascending to erect, 1-3 cm; internodes to 12 x 0.5-1.2 mm; adventitious roots usually 2-4 at a node. Leaves opposite, to 12 mm; in erect parts of the shoot leaves are erectopatent, in prostrate parts petioles are mostly erect but leaf-blades often horizontal; petiole gradually widening to the blade, (2-)4-10 mm, ratio petiole/blade length in grown-up leaves c. 1-2.5, in terrestrial plants and in young shoots c. 0.8-1; blade obovate to elliptic to ovate, (2-)3-4 x (1-)1.5-2 mm; base long-attenuate; apex obtuse to rounded; veins pinnate; hydatodes obscure; stipules narrowly triangular, 0.7-0.8 x 0.25 mm, usually with lobelike, long, narrow teeth and long acute apex.
Flowers single at the nodes, short-stalked or rarely sessile (pedicel at fruit stage 0.1-1.5(-4.0) mm, often bent sideward from the leaf axil). Sepals 4, slightly connate at base,all alike, elliptic, 0.45-0.8 x 0.3-0.45 mm (usually slightly shorter than the petals), apically green, with 0-1 filiform teeth at the middle of each side. Petals 4, elliptic, 0.6-1.0 x 0.3-0.5 mm. Stamens 8. Carpels 4. Capsule almost cylindrical (slightly narrowing upwards), somewhat depressed at apex, wider than or sometimes as wide as long, 0.8-1.1 x 1.0-1.35(-1.8) mm; walls irregularly broken when opening. Seeds regularly arranged, parallel, mostly in ± upright position, 8-24, cylindrical, straight to bent at apex to slight j or s form (rarely up to an angle of 90º), 0.7-0.8 x 0.2-0.25 mm, pale greenish brown to pale brown; pits inconspicuous, 35-40 in each row, 0.01-0.02 x 0.035-0.040 mm. - Mid-summer to late summer.
Distribution. BNem-MBor. Alt. S Jmt 299 m. - N fairly common in Øf, Ak and He; rare in Op (Lillehammer 1931-1939, Østre Toten 1996, Øyer 1984) and Bu; Te Skien 2002, Ho Voss 1999, 2002, MR Surnadal 1929, NT Trondheim (Namdalen) 1930. S fairly common in Vrm, rarer in BhG, Vg and Dlr; more common along the coast northwards in Mpd Hudiksvall 1883, Sundsvall 1885, Selånger 1885-1952, Ång Sollefteå 1975, Vb Holmsund 1981, Falbäcken 1891, Rödån 1980, 1986, Sörfors 1974, Umeå 1864, 1965, and fairly common in southern part of Nb; Hl Falkenberg 1911, Ås 1910, 1929, Dls Frändefors 1893, 1925, Srm Kung Karl, Strängnäs 1846-1864, Upl Solna 1864, Vaksala 1921, Ängsö, Vsm Kungsör, Gst Gävle 1837-1863, Kågbo 1988, Hls Ljusdal 1914-1936, Bollnäs 1947, Jmt Mattmars 1936, Berg 1973, LL Gällivare 1969, 1970. Probably declined especially in southern and eastern provinces. F fairly frequent in inland South and Central Finland from St to PK and southern Kn, coastal OP and coastal PeP, rare in V Karkkila, Lohja, Nummi-Pusula, Salo, Vihti; U Espoo 1940, Porvoo 1996-2001, Artjärvi 1856, Pyhtää 1982; EK Ylämaa 1975, 1978; fairly rare in EP and KP, inland PeP to the Polar Circle, Ks Salla 1971 and KiL Muonio 1947, 1972.
Outside Norden known from the adjacent Russia (the Republic of Karelia and St. Petersburg) and Germany (Schleswig-Holstein and Bavaria).
Habitat. Mostly in shallow water (usually at less than 50 cm depth, hardly ever deeper than 1 m), sometimes on wet soil above shoreline. On bare soil or among very sparse taller vegetation on silt or sand, sometimes on gravel, clay or gyttja. Meso-eutrophic lakes and rivers; in brackish water only in the least saline coasts and river estuaries in the Bothnian Bay and Gulf of Finland; very rarely in temporary pools on shores. Often in man-influenced sites such as grazed shores and boat harbours. A weak competitor, declining due to loss of open habitats and heavy eutrophication of waters.
Taxonomy. Elatine orthosperma has often been treated as a variety or subspecies of E. hydropiper because of the lack of good separating characters other than the shape of seeds and capsules (which are possibly correlated). This view was not adopted here. Although there is some variation in the seed shape of E. orthosperma, no individual with truly intermediate seeds has been found. Also the difference in fruit form is distinct. Further, there are slight differences between E. hydropiper and E. orthosperma in vegetative characters, especially in pedicel length, but also in robustness and leaf form, and the two taxa have somewhat different ecological and distributional patterns. The area of E. orthosperma is completely sympatric with that of E. hydropiper but more limited. But apparently the taxa are very close to each other, and further studies (e.g. growing experiments or DNA studies) are needed to clarify their relationships.
Similar taxa. Elatine orthosperma is vegetatively very similar to E. hydropiper (4), see that species. - E. orthosperma is sometimes mixed up with E. triandra because of the fairly similar seeds. However, the seeds of E. orthosperma are slightly bent near the end (J- or S-shaped), while seeds of E. triandra are bent at the middle; E. orthosperma seeds are also longer, have a less prominent surface pattern, and are fewer per capsule.
References To top
Larsen, K. & Pedersen, A. 1960: Papaveraceernes, Fumariaceernes, Nyphaeaceernes, Ceratophyllaceernes, Elatinaceernes, Halorrhagidaceernes, Hippuridaceernes og Lythraceernes udbredelse i Danmark. Bot. Tidsskr. 56: 37-86.