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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: shortstemmed eelgrass

Synonyms and Other Names: V. spiralis × V. denseserrulata

shortstemmed eelgrass

Identification: According to Wasekura et al. (2016):

Habit: submerged perennial forb

Roots/Stems: fibrous roots; leafless and tuberless stolons; lignified stems

Leaves: rosettes of linear, tape-like leaves up to 0.7 m long and 3-13 mm; leaf margins sometimes toothed, leaf apex usually round

Flowers: only female (pistillate flowers) known; spiralling scape up to 0.7 m long; thin, translucent spathe surrounds single flower with three sepals

Seeds: unknown

Diagnostic features: lignified stems above the sediment and a green lacunal band along the middle of the leaves (Gebhart et al. 2025), although hybrid morphology is not consistent; genetic testing is preferrable (see Tringali et al. 2023).

Size: Usually under 20 cm but up to 70 cm tall

Native Range: Hybrid of two disjunct parent species, Vallisneria denseserrulata Makino and Vallisneria spiralis L., from east Asia and Eurasia/Africa, respectively (Ghafoor 1985, Wu and Raven 2010, Wasekura et al. 2016).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology:

Habitat: creeks, rivers, sloughs, impoundments, stable water levels and low flow (Wasekura 2016).

Life history: only female plants are known. Spread is entirely vegetative as parent species are not present in the U.S. Grows in dense submerged patches while also floating mats are known to assist spread. Flowers bloom in fall months (Wasekura 2016, Gorham et al. 2021).

Tolerances: low to freezing temperatures (Gebhart et al. 2025)

Means of Introduction: Likely hybridized in cultivation either intentionally or accidentally as both parents are common in the aquarium trade (Wasekura 2016, Martin and Mort 2023). Secondary spread likely due to aquarium releases, (un)intential plantings for habitat restoration purposes, hitchhiking on watercraft, and downstream dispersal in floating mats (Gorham et al. 2021, Gebhart et al. 2025).

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological

References: (click for full references)

Beets, J.P., E.J. Haug, B.P. Sperry, R.A. Thum, and R.J. Richardson. 2024. Response of four Vallisneria taxa to aquatic herbicides. Invasive Plant Science and Management 17:297-304. https://doi.org/10.1017/inp.2024.33.

Gebhart, M.G., S.A. Schmid, S. Turner, D. Webb, R. Thum, J. Beets, and G. Turnage. 2025. Invasive eelgrass hybrid (Vallisneria × pseudorosulata) in the southeastern United States. Invasive Plant Science and Management 18(1):1-5. https://doi.org/10.1017/inp.2024.37.

Ghafoor, A. (1985). Flora of Pakistan 169: 1-13. Department of Botany, University of Karachi, Karachi.

Gorham, S.B., S. Seyoum, B.T. Furman, K.M. Darnell, L.K. Reynolds, and M.D. Tringali. 2021. Molecular detection of a non-native hybrid eelgrass, Vallisneria spiralis Linnaeus (1753) × V. denseserrulata Makino (1921), in the southeastern United States. Aquatic Botany 175:103445. https://doi.org/10.1016/j.aquabot.2021.103445.

Martin, A.P. and M.E. Mort. 2023. Vallisneria (Hydrocharitaceae): novel species, taxonomic revisions, and hybridization. Aquatic Botany 188:1-9. https://doi.org/10.1016/j.aquabot.2023.103669.

Tringali, M.D., S.B. Gorham, S. Seyoum, C. Puchulutegui, M.S. Bass, B.T. Furman, and C. Mallison. 2023. A PCR assay for the detection of introduced Vallisneria spiralis, V. denseserrulata and their hybrids. Conservation Genetics Resources 15:125-133. https://doi.org/10.1007/s12686-023-01311-9.

Wasekura, H., S. Horie, S. Fukii, and M. Maki. 2016. Molecular identification of alien species of Vallisneria (Hydrocharitaceae) species in Japan with a special emphasis on the commercially traded accessions and the discovery of hybrid between nonindigenous V. spiralis and native V. denseserrulata. Aquatic Botany 128:1-6. https://doi.org/10.1016/j.aquabot.2015.09.002.

Wu, Z. & Raven, P.H. (eds.) (2010). Flora of China 23: 1-515. Missouri Botanical Garden Press, St. Louis.

Author: Pfingsten, I.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.