Rorippa sylvestris (L.) Besser, 1821

Rorippa sylvestris (L.) Besser, 1821 View in CoL

Rorippa sylvestris (L.) Besser View in CoL , Enum. Pl. Volh.: 27 (1821) — Sisymbrium sylvestre L. View in CoL , Sp. Pl.: 657 (1753).

Distribution

Native distribution

Europe (Northern Europe excepted), Asia Minor, Caucasus, Iran.

Secondary distribution

Northern Europe, Northern, Central and Eastern Asia, China, Northern Africa, Northern and Southern America. In its northern limit, the species reaches as far as the true Arctic in Iceland and Svalbard ( Wasowicz et al. 2019). In Northern Asia, it is found across southern Siberia and in the Far East ( Chepinoga et al. 2024). The species is highly invasive, at the active stage of expansion ( Ebel 2016).

Jonsell (1968) has analysed the early records of Rorippa sylvestris in North-Western Europe (from the Great Britain to Finland) and concluded that the oldest pathway of its dispersal was with ship ballast and boat traffic, but this pathway became obsolete already in the 19 th century and the early arrivals made no practical contribution to the recent invasion. The dramatic increase in the species distribution in Northern Europe was apparently connected with the intense gardening and transportation of the garden commodities, which has been especially noticeable since 1915 ( Jonsell 1968).

The distribution, spread and invasion potential of Rorippa sylvestris in Siberia, a large region adjacent to Central Asia, have been described in detail and documented by A. Ebel ( Ebel 2000, Ebel 2016). He noted that the species was first collected as a weed in the botnical garden of the Tomsk University as early as 1925 and in many populated places in more recent times, thus indicating its arrival with gardening and garden commodities. Very remarkably, its numerous rather early records in 1933 and then in the 1960 s- 1990 s are linked with the occurrence in natural wetland habitats, supporting the idea that the species may have been partly dispersed by waterfowl - at least spreading locally in this way, but likely also involving long-distance dispersal from man-disturbed habitats colonised by the species ( Ebel 2000).

In North America, Rorippa sylvestris has been common in the main area east of the Mississippi River in north-eastern United States and southern Canada ( Rollins 1981), where it occurs in natural wet habitats along rivers and waterbodies and in gardens, with the first record published in 1818 ( Stuckey 1966, Stuckey 1972). Similarly to the situation in Sweden ( Jonsell 1968) and Siberia ( Ebel 2000, Ebel 2016), the broad occurrence or even prevalence of the plants in natural habitats required the researcher to undertake special analysis to obtain evidence for an introduced status in the New World. The first species colonies appeared as a result of long-distance dispersal, mostly to large sea and river ports ( Stuckey 1966). Groh (1936) noted that the species was spread mostly with nursery stock in the 20 th century, whereas Stuckey (1966) considered rivers as a major corridor in the secondary dispersal.

Scattered records of Rorippa sylvestris at mills ( Hanssen and Nordhagen 1930) indicate its potential ability to immigrate as grain contaminant. It is known to occur as impurity in grass seed ( Salisbury 1961), thereby spreading to city lawns.

Both in its native and secondary distribution area, the species may abundantly invade cultivated lands on fertile soils and with sufficient water supply. Notably, its abundant occurrence in forest nurseries in Sweden ( Bärring 2008) indicates a strong potential of the species to infest almost any kind of rooted saplings in commercial distribution, which played a major role in its secondary dispersal by man.

Distribution in Central Asia

Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan (Fig. 23 View Figure 23 ).

In Central Asia, Rorippa sylvestris was first recorded in Uzbekistan, where it was found in a garden in Tashkent ( Popov 1924). The documenting specimen was collected in 1919. Since then, the species has been repeatedly collected or observed as a weed or ruderal plant in Tashkent and keeps its presence as noted in recent local observations (e. g. Tillaev and Gaziev (2021)). It was also found in ruderal places in Samarqand in 1940 ( Botschantzev and Vvedensky 1955) and Qarshi in 2024 ( iNaturalist 2024).

The occurrences in Tashkent and Samarqand remained isolated in Central Asia until rather recent times ( Shermatov 1974).

The first species record from Kyrgyzstan, noting its occurrence in Bishkek and vicinities ( Jonsell 1973), has been commonly neglected in regional literature. The species distribution in the country is detailed for the first time in our present work.

In Tajikistan, the species has been found in 1982 in the botanical garden of the Academy of Sciences in Dushanbe, as a weed in ornamental cultivation and as a ruderal plant along irrigation ditches ( Dorofeev 1984). It was subsequently observed in the city in 2017-2018 ( Ebel et al. 2020).

In Kazakhstan, the species was first found along rivers within two large towns, Ust-Kamenogorsk in 1967 and 2002 ( Ebel 2000, Ebel 2002) and Semipalatinsk in 2002 ( Ebel 2002, Ebel and Ebel 2003).

Distribution in Kyrgyzstan

Western Tian-Shan, Northern Tian-Shan (Fig. 24 View Figure 24 ).

Rorippa sylvestris was first collected in Kyrgyzstan in 1955, near Jangy-Jer Village in the Chüy Depression, north of Bishkek City. In the same area, the species was subsequently collected in Bishkek (city centre) and along the Ala-Archa River which streams from the mountains through Bishkek. To date, the plants have been found in several places along this river (Fig. 25 View Figure 25 ), from the mountains to the lowland.

One more historical locality, also dated 1955, is known from the walnut forest area near Arstanbap Village. This locality has not been taken into account in the previous publications ( Sennikov and Lazkov 2024 a) and is formally reported as a new record here.

The localities are situated in the lowlands (700-800 m a. s. l.), foothills (1150 m a. s. l.) and the lower mountain belt (1300-1700 m a. s. l.).

Ecology

Moist meadows and riversides in the southern forest zone in the native distribution area. Riversides and inundated places, cultivated lands, lawns, roadsides and ruderal places in the secondary distribution area. Although the species is typically associated with wet habitats, it can endure extensive periods of drought; this ability allows it to colonise ruderal habitats ( Salisbury 1961).

Biology

Perennial, rhizomatose.

Although the seed set may be limited because of a high level of self-sterility in monoclonous or genetically-poor introduced populations, it is compensated by the ability to actively disperse by root fragments ( Stuckey 1966). The species has a strong ability to persist in cultivated lands due to rooting at nodes of its prostrate stems and regeneration from small fragments of rhizomes ( Salisbury 1961).

Taxon discussion

Three ploidy levels (tetraploid, 2 n = 32; pentaploid, 2 n = 40; hexaploid, 2 n = 48) are known in the secondary distribution area ( Jonsell 1968). The Central Asian plants have not been karyologically tested.

Hybrids between Rorippa sylvestris and R. austriaca are common when the species co-occur in their either native or secondary distribution ( Bleeker 2007). Such hybrids are invasive in Europe and the hybridisation seems to facilitate their invasion ( Bleeker 2003, Bleeker and Matthies 2005). The hybrid ( R. armoracioides (Tausch) Fuss ) has already been collected in Uzbekistan in 1954 ( Jonsell 1973) and in north-eastern Kazakhstan in 2002 ( Ebel 2002). It remains unknown in other countries of Central Asia.

Introduction to Kyrgyzstan

Period of introduction

Neophyte.

As the species is rather conspicuous, it is unlikely that its occurrence has long been neglected in the proximity to the capital and its botanical activities (cf. Stuckey (1966), Jonsell (1968), Ebel (2000)). With the first herbarium collections made in 1955, we may safely assume that the species was introduced in the late 1940 s or early 1950 s.

Pathways of introduction

Transport – Contaminant: Contaminant nursery material.

Since 1948, when the Communist Party of the USSR and the Soviet Government had announced that forest plantations are crucially important for agricultural productivity, territories of the Chüy Depression near Bishkek in Kyrgyzstan were involved in experimental planting of forest trees ( Karafa-Korbut 1955). At that time period, planting trees became common also in the mountains, including nature reserves, as part of the programme for " improving " natural forests (e. g. Kotlar (1973)); we have observed remnants of such planting in many places in Kyrgyzstan, for example, the Sary-Chelek Nature Reserve ( Lazkov and Ganybaeva 2021).

All occurrences of Rorippa sylvestris in Kyrgyzstan are linked to forest plantations (the oldest records in the Chüy Depression, Ala-Archa River and a walnut forest area near Arstanbap Village) or ornamental cultivation (Bishkek City). We assume nursery transport to be responsible for all these introductions.

The secondary dispersal may occur by waterflow and by water birds along watercourses.

Source of introduction

Eastern Europe.

Invasion status

Naturalised.

The localities in the city may be ephemeral because of constant management, but the species is known as naturalised along the Ala-Archa River (recent observations in 2023: iNaturalist (2024)).

Evidence of impact

Agriculture - minor impact (the species is known as a weed of ornamental cultivation, although with low frequency and very limited distribution). Native ecosystems - minor impact (the species is locally spreading along natural and artificial watercourses). Urban areas - minor impact (the species occurs as a ruderal along pavements and irrigation ditches in populated places, with limited distribution).

Trend

Gradually increasing. The species is slowly expanding in native habitats and becoming more noticeable in the city.