V. spiralis is considered to be native to southern Europe, northern Africa, the Middle East, and southwest Asia. Over the last century, the species has spread into central, northern and northwestern Europe, particularly into artificially he...
V. spiralis is considered to be native to southern Europe, northern Africa, the Middle East, and southwest Asia. Over the last century, the species has spread into central, northern and northwestern Europe, particularly into artificially heated water bodies (Hussner and Lösch, 2005; Hutorowicz, 2006; Hutorowicz and Hutorowicz, 2008; Katsman and Kuchkina, 2009). There are also geographically disjunct introductions to the United Kingdom, North America, the West Indies and New Zealand. The use of the species as an aquarium plant, together with its ability to spread vegetatively, is considered to have facilitated its spread and invasiveness.
Vallisneria spiralis is the type species of the genus Vallisneria, described by Linnaeus (1753) from its native habitat in southern Europe (Lowden, 1982). Worldwide, twelve species have been recognized recently by molecular techniques and a further 2-3 by morphological differences that were invariant at the molecular level (Les et al., 2008).
Although two varieties of V. spiralis were recognized by Lowden (1982), Vallisneria spiralis var. spiralis and Vallisneria spiralis var. denseserrulata Makino, molecular study supports the separation of these taxa as distinct species: V. spiralis and Vallisneria denseserrulata (Les et al., 2008).
The name V. spiralis has a history of being applied indiscriminately to similar rosette plants from Asia, Australia, Europe and North America (Jacobs, 2010). Recent studies indicate a more restricted native distribution but, particularly in south-west Asia and northern Africa, more detailed studies seem necessary to resolve species distributions. Australian records of V. spiralis var. denserrulata (Lowden, 1982) and Vallisneria spiralis var. procera(Rodway, 1896) have since been determined to be Vallisneria nana (Jacobs and Frank, 1997) and Vallisneria australis (Les et al., 2008), respectively.
Although genetic analysis has not been carried out on V. plants in New Zealand, morphological study has resolved there to be two naturalized species in that country: V. spiralis and V. australis (P Champion, NIWA, New Zealand, personal communication, 2010). However, Pacific Island records of V. spiralis, in the Hawaiian Islands (Staples et al., 2003) and New Caledonia (MacKee, 1994) warrant further investigation and confirmation given the comment by Jacobs and Frank (1997) that “V. spiralis is a temperate / warm temperate species in its narrowest interpretation”. In Australia, the tropical species are V. nana, Vallisneria triptera, Vallisneria annua and Vallisneriaerecta, replaced by V. australis in temperate areas (Jacobs and Frank, 1997; Les et al., 2008). Contrary to this, plants of V. spiralis from Lake Edward in equatorial Africa do align genetically with plants from southern Europe (Les et al., 2008).
Freshwater plants with fibrous roots, short stem, horizontal runners, and submerged, linear, strap or tape shaped leaves up to 10 mm wide and 100 cm or more long arranged in a basal rosette; leaves with three to five parallel nerves, entire to finely toothed margins. Plants dioecious; inflorescence axillary. Staminate plants with numerous, minute imperfect flowers enclosed by a dehiscing two-valved, reflexed spathe, flowers with three sepals, one minute petal rudiment, one staminodium and two stamens; scapes thin, 1.0-1.3 mm wide, 10–30 mm long, flowers slightly zygomorphic, with obliquely extended stamens, hairs absent at base of androecium, staminodia adnate near the apex of the fused stigmatic lobes, with lobes shallowly cleft and conspicuously fringed. Pistillate plants with inflorescence subtended by a bivalve spathe; scapes long, extended to spirally coiled; flowers solitary, slightly zygomorphic, with three sepals 2.0–3.5 mm long, three minute transparent petal rudiments, three staminodia and three bifid stigmas borne on short, or highly reduced styles; staminodia small, inconspicuous, adnate to fused discordant stigmatic lobes; stigmas fringed; floral incision deepest between matching stigmatic lobes. Ovary inferior, unilocular; fruit elongate, approx. 9.5–10.0 cm long, ellipsoid, indehiscent; placentation parietal; seeds numerous, ellipsoid, striate, 1.3–2.0 mm long; endosperm absent (Lowden, 1982).
Descriptions and figures: Lowden (1982: 285, fig. 3a-j).
Widespread in tropical and subtropical areas of both hemispheres. Native to southern Europe, northern Africa, the Middle East and southwest Asia, but now spread to the north and northwest in France, Belgium, Netherlands, southern Britain, Poland and Russia. Introduced to North America, West Indies, New Zealand, New Caledonia and the Hawaiian Islands (but note comments under taxonomy regarding Pacific Island records).
Although commonly reported from India (e.g. Jana and Choudhuri, 1979; Rai et al., 1995), Lowden (1982) assigned most specimens he studied from India, Pakistan and Bangladesh, along with those from South-East Asia, to V. spiralis var. denseserrulata. As var. denseserrulata is now considered a separate species (Les et al., 2008), clarification is needed on the identity and distribution of V. species though Asia.
In New Zealand, V. australis is present in Lake Pupuke and nearby, where it was first recorded in 1896 (Cheeseman, 1896). Only male plants are known, and this population has been variously recorded as V. spiralis, V. gigantea (e.g. de Winton et al., 2009), and V. americana (P Champion, NIWA, New Zealand, personal communication, 2010). Specimens cited as V. gigantea from the Avon River in the Canterbury region and at South Kaipara Head near Auckland (Healy and Edgar, 1980) are now considered to be misidentifications (de Winton et al., 2009).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Les et al. (2008) report what they consider to be the first authentic record of V. spiralis in North America, with the material collected in Texas. Previous reports of the species in North America are considered to be misidentifications of V. americana. Lowden (1982) did not find evidence of the species in the Americas, but reported “minor” introductions into Jamaica and Cuba.
In New Zealand, V. spiralis is reported to have been present on the North Island in Lake Wiritoa in the Manawatu-Wanganui region, since 1978, and Meola Creek in the Auckland region since 1982 (de Winton et al., 2009). From 2001 to 2008, the species was documented from 82 sites in the Wellington region, mostly in garden pools. Since 2000 it has also been reported from the Northland region and the Opawa River at Blenheim in the Marlborough region on the South Island (de Winton et al., 2009; P Champion, NIWA, New Zealand, personal communication, 2010).
The species is also reported from the Hawaiian Islands (Staples et al., 2003) and New Caledonia (MacKee, 1994). In the Hawaiian Islands V. spiralis was found during freshwater stream survey projects to be locally naturalized and abundant on O’ahu, where it formed dense underwater mats that are the dominant vegetation in areas where found (Staples et al., 2003). As previously mentioned, these Pacific Island records warrant confirmation in the light of recent taxonomic study of V. spiralis.
Willby (2007) comments that, with respect to climate change, aquatic plants that are not at present invasive in the United Kingdom, including V. spiralis, may become so if climate change relaxes the barriers to growth. Similar comments are made by Hussner and Lösch (2005), who suggest that the species could become naturalized through Western and Central Europe if average temperatures rise by only one or two degrees.
Static or flowing freshwater habitats, including lakes, ponds, water courses, and wetlands.
In the River Nile, in a study to assess the impact of river vessel traffic on aquatic vegetation, V. spiralis was found to be tolerant of high wave disturbance (Ali et al., 1999). As an exotic in the River Erft, V. spiralis was found in stagnant, slow and fast running (up to 0.8 m/s) water to depths of 1 m, and on muddy, sandy or gravelly sediment (Hussner and Lösch, 2005). The species preferred clear water, with growth retarded in turbid water. In New Zealand in depths of less than 9 m (Auckland Regional Council, 2010a).
Vallisneria is one of several genera in the Hydrocharitaceae in which staminate flowers detach completely from a spathe at the base of submerged male plants (Les et al., 2008). The flowers rise to the surface and open to form free-floating, raft-like structures which are dispersed by wind and currents. In this genus, as in two other genera in the family (Maidenia, Nechamandra), the pollen remains dry within elevated anthers and the anthers also remain dry within the perianth of the pistillate flower (Les et al., 2008). The pistillate flowers, attached to submerged plants by long, flexuous peduncles, orient their opening at the water surface and pollination occurs when anthers of the floating staminate flowers contact the stigmas of the pistillate flowers. After fertilization the peduncle coils into a spiral, thus drawing the developing fruit underwater where it matures (Les et al., 2008).
An experimental study into the photosynthetic, photorespiratory and respiratory behaviour of three aquatic angiosperms, including V. spiralis, found that under constant conditions of light, temperature and initial gaseous composition there was considerable variation in the rates of dark and light respiration, as well as photosynthesis (Jana and Choudhuri, 1979). All three species were assumed to be basically C3 plants, since all showed photorespiration. Both photosynthesis and respiration rates generally declined with leaf age, with a possible increase in the rate of respiration with the approach of senescence.
Only female plants are known in New Zealand (P Champion, NIWA, New Zealand, personal communication, 2010).
In the River Erft, V. spiralis mostly grew in association with the native Sparganium emersum (Hussner and Lösch, 2005). V. spiralis dominates depths to 1.0 m, with S. emersum in the deeper more turbid waters. Where the species are not in competition, both occupy a broader niche.
Local dispersal can be by both seed and runners. Waterfowl, flooding or human disturbance in flowing water can cause small fragments to break from the parent plant and form new colonies (Greater Wellington Regional Council, 2004 in ISSG, 2010).
V. spiralis, along with Egeria densa and Myriophyllum aquaticum, are considered most likely to have been introduced to the River Erft in Germany as aquarium waste (Hussner and Lösch, 2005).
V. spiralis can form dense beds which displace other species of submerged hydrophytes (MAF Biosecurity New Zealand, 2010). In Polish lakes, this is attributed to its clonal mode of propagation and its maximum growth in autumn when native species are dormant (Hutorowicz, 2006; Hutorowicz and Hutorowicz, 2008). In other areas, such as in the River Erft in Germany, a dynamic arrangement of native and exotic species has resulted in a high a-diversity of primary producers which is considered to possibly have a positive influence on community composition (Hussner and Lösch, 2005).
Rooted submerged plant species are considered to have value for phytoremediation because of their soil binding roots, rhizomes and stolons which help facilitate colonization by benthic algae, other microbes and invertebrates (Vajpayee et al., 2001). V. has been found to reduce chromium, cadmium and copper levels in water under laboratory conditions (Sinha et al., 1994; Vajpayee et al., 2001). From the studies showing V. to effectively remove chromium from tannery effluent, the plant was proposed as suitable for the construction of wetlands for the amelioration of chromium containing waste water, with the proviso that methods for safe disposal of contaminated plants would be necessary (Vajpayee et al., 2001). However, in a study on the potential of aquatic plants to remove heavy metals from wastewater, V. spiralis was the least effective of the plants tested (Rai et al., 1995).
Experiments have also demonstrated the potential utility of V. spiralis for photoremediation of pulp and paper mill and distillery effluents (Singhal et al., 2003). Plants were effective in reducing COD, colour and sodium content of effluents.
Lowden (1982) used floral characters to separate rosulate V. species, and recognized only two: V. spiralis and V. americana. V. spiralis was delimited on the basis of stamens having free filaments not subtended by hairs and stigma lobes fringed and deeply divided. V. americana possessed fused filaments, androecial hairs, and unfringed, shallowly lobed stigmas. Lowden further subdivided V. spiralis into two varieties: var. spiralis, in which the minute staminodia originated near the apex of the fused stigma lobes, and var. denseserrulata, in which the minute staminodia nearer the base of the stigmalobes. The taxonomic system proposed by Lowden (1982) has since been considered problematic because it did not include vittate species and because of variability in the floral features he utilized (Les et al., 2008). Studies using morphological and molecular data support the retention of V. denseserrulata as a species.
V. denseserrulata differs to V. spiralis in having acute, rather than obtuse or rounded apices on mature leaves, longer peduncles (> 100 cm), and flattened, not ovoid, fruit cross sections (Les et al., 2008). V. spinulosa has similar differences to V. spiralis as V. denseserrulata, but additionally has fruit that are winged and triangular in cross-section.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
In New Zealand, V. spiralis is listed as a “surveillance pest plant”, and the pest strategy is to prevent their establishment or spread by prohibiting their sale, propagation, distribution and exhibition (Auckland Regional Council, 2010b). Entry to New Zealand is prohibited under national biosecurity regulations.
In New Zealand, the species is considered virtually impossible to eliminate once established, but small infestations can be controlled by divers hand-pulling plants (Auckland Regional Council, 2010a). Interference with established beds can make the problem worse by spreading viable vegetative fragments.
Some generalist herbivorous fish, such as grass carp, have been proposed as biocontrol agents to reduce the biomass of aquatic pest plants in an area (Froude, 2002). However, Froude adds that browsing is not species specific, and both favoured and undesirable plants will be consumed.
Genetic studies across the genus V. have demonstrated that the name V. spiralis has been applied to a number of morphologically similar species (Les et al., 2008). Outside of it now recognized native range in southern Europe, such as in New Zealand, New Caledonia and the Hawaiian Islands, molecular confirmation of species identity is needed.