The Venice Lagoon has 81 named plants and seaweeds in its most recent survey: four seagrasses growing underwater, 25 salt-tolerant plants on the barene, and about 52 seaweeds and algae. Three campaigns between 2023 and 2025 collected them, and DNA barcoding rather than the eye alone settled the names (Drigo et al., 2026).
That survey is the first inventory of the lagoon's photosynthetic life to check its identifications molecularly, and the checking changed a lot of answers. DNA disagreed with the field identification for 44.64 per cent of the seaweed samples and 29.41 per cent of the vascular plant samples (Drigo et al., 2026, p. 10). The same work confirmed all four seagrass species previously known from the lagoon, added the yellow-green alga Vaucheria litorea as a first record, and found the non-native cordgrass Sporobolus anglicus at every salt marsh it surveyed while the native Sporobolus maritimus was missing from three (Drigo et al., 2026, pp. 13, 14, 20).
This page sets out what the four seagrasses are and where each one grows, which plants cover the barene, the cordgrass that is displacing a native one, the two big brown seaweeds that form the lagoon's underwater canopy, and why naming any of this takes a laboratory. The survey is a bioRxiv preprint and has not been peer reviewed, so every figure below should be read as a 2026 research finding rather than a settled count.
What plants grow in the Venice Lagoon?
Eighty-one taxa, counted across three field campaigns in 2023, 2024 and July 2025. The split by major group is 13 green algae (Chlorophyta), 11 heterokonts of which 10 are brown algae and one is a yellow-green alga, 28 red algae (Rhodophyta) and 29 vascular plants (Drigo et al., 2026, pp. 1, 10). Sixty-one of the 81 are pinned to a species and the remaining 20 only to a genus, which reflects how hard several of these groups are to separate by eye (Drigo et al., 2026, pp. 3, 10).
Counted from the survey's own species table, the 29 vascular plants divide into 4 seagrasses and 25 halophytes, the salt-tolerant plants of the barene (Drigo et al., 2026, pp. 11 to 12). That leaves about 52 taxa of seaweed and algae, which is where most of the lagoon's photosynthetic diversity sits even though almost none of it is visible from a vaporetto.
The context the plants live in is a brackish lagoon, not the sea. Surface salinity across the lagoon runs at roughly 12 to 36 PSU, close to Adriatic water at the three inlets and far fresher near the river mouths (Sankara Narayanan et al., 2026, p. 10). Red algae dominated the seaweed list, and no charophytes were found at all, an absence the authors read as a legacy of the historical reduction in freshwater reaching the lagoon (Drigo et al., 2026, p. 18).
The four seagrasses, and where each one grows
The lagoon has four seagrasses, and the 2023 to 2025 survey found every one of them: Cymodocea nodosa, Zostera marina, Zostera noltii and the genus Ruppia (Drigo et al., 2026, pp. 11 to 12, 19). The World Register of Marine Species records Zostera marina in English as eelgrass, Zostera noltii as dwarf eelgrass and Cymodocea nodosa as little Neptune seagrass (WoRMS Editorial Board, 2026).
Two of them are everywhere. Cymodocea nodosa and Zostera marina were recorded in all three lagoon sectors in all seasons, and the survey calls them the most frequent, which matches monitoring from twenty years earlier (Drigo et al., 2026, pp. 13, 19). The other two are seasonal or local. Zostera noltii turned up in every sector in spring, was not detected at all in summer, and in autumn appeared only in the northern lagoon (Drigo et al., 2026, p. 13).
Ruppia is the one worth knowing about if you ever walk a barena. It is the rarest of the four, found only in the southern and central sectors, and it lives mainly in the ponds inside the salt marshes rather than in open water (Drigo et al., 2026, pp. 13, 19). Even with DNA, the survey could not decide whether its samples were Ruppia maritima or Ruppia cirrhosa. What all four do is hold the bottom together: their root mats compact and stabilise the sediment and reduce resuspension (Drigo et al., 2026, p. 19).
The barene plants: glassworts, rushes and sea lavender
Twenty-five salt-tolerant plants were recorded on the barene. Four of them are glassworts in the genus Salicornia, including the shrubby Salicornia fruticosa; three are rushes in the genus Juncus; three are sea lavenders in the genus Limonium; and four are cordgrasses in the genus Sporobolus (Drigo et al., 2026, pp. 11 to 12). The rest include common reed (Phragmites australis), sea purslane (Atriplex portulacoides), annual sea-blite (Suaeda maritima), under the English names held in the World Register of Marine Species (WoRMS Editorial Board, 2026). GBIF records the genus Salicornia in English as glasswort and samphire, and Limonium narbonense as swamp sea-lavender (GBIF Secretariat, 2026).
Two of the finds are rediscoveries. Only Limonium narbonense had been reported in the lagoon in the 21st century, and DNA barcoding added Limonium virgatum alongside it. Juncus acutus and Juncus gerardii, both recorded in the central sector, had not been reported in the lagoon this century either (Drigo et al., 2026, p. 20).
Plant-minded visitors should look south. The highest number of halophyte species was recorded in the southern sector, which the authors put down to those marshes sitting close to dry land, and five taxa were found there and nowhere else: Artemisia, common reed, Salsola, Thinopyrum acutum and Triglochin maritima (Drigo et al., 2026, pp. 13, 19). One caveat belongs with that: some of the marshes sampled were artificial, standing higher than the natural ones with less salt in the soil (Drigo et al., 2026, pp. 19 to 20).
The cordgrass problem: one non-native at every site
The sharpest finding in the survey concerns three near-identical grasses. Sporobolus anglicus, a non-native, was recorded at every salt marsh surveyed in the 2025 campaign. The native Sporobolus maritimus was not detected at three of them (Drigo et al., 2026, pp. 14, 21). The conclusions put it plainly: the absence raises concerns about the native's persistence (Drigo et al., 2026, p. 22). The World Register of Marine Species lists these two under their older genus name Spartina, as common cord-grass and small cord-grass (WoRMS Editorial Board, 2026).
The third grass settles a twenty-year argument. Sporobolus x townsendii, a sterile hybrid, was first reported in the lagoon in the early 2000s, after which other studies suggested those records were really Sporobolus anglicus, leaving the question open (Drigo et al., 2026, p. 20). The 2025 campaign collected 105 plants, 34 in the south, 31 in the centre and 40 in the north, and resolved the three by genome size: the hybrid carries roughly half the genome of Sporobolus anglicus, close to that of the native (Drigo et al., 2026, pp. 13, 14). It was confirmed at four sites in the southern and central lagoon, and at none in the north.
Being sterile, the hybrid can only creep outward vegetatively, which limits how far it spreads (Drigo et al., 2026, p. 21). Sporobolus anglicus has no such limit, and the authors describe it as a vigorous and aggressive perennial and a non-indigenous species of the highest concern.
The lagoon's two canopy seaweeds, and the heat they face
Two brown algae form what canopy the lagoon has. Fucus virsoides was recorded in the southern sector in spring and the central sector in summer. Gongolaria barbata was found in the central sector in spring and summer and in the northern sector in autumn, and the survey notes it as still widespread across the whole lagoon (Drigo et al., 2026, pp. 13, 19).
Fucus virsoides carries a genuine superlative: it is the only endemic representative of the genus Fucus in the Mediterranean, and it has declined significantly over recent decades, with the causes still unclear (Drigo et al., 2026, p. 19). It was not recorded in the northern sector at all during the survey. Gongolaria barbata faces a measurable threat instead of an unexplained one: recent work cited by the survey found mortality rising after exposure to temperatures above 34 degrees Celsius, which matters in a lagoon this shallow (Drigo et al., 2026, p. 19). For how often the lagoon now reaches high summer temperatures, see our page on how often MOSE will close.
There is a quieter signal in the group counts. Brown algae came out poorer in species than red algae, and because several brown algal taxa are associated with relatively unpolluted water, the authors suggest this may point to a decline in ecological quality. They immediately qualify it: habitat availability, season and sampling effort could produce the same pattern (Drigo et al., 2026, p. 18).
The bricole: the lagoon's other plant habitat
The survey worked two habitats, and both are things a visitor sees from a boat. One is the barene, the salt marshes, where plant presence was recorded along 30 metre lines run parallel to the shoreline at increasing distances from it. The other is the bricole, the wooden mooring poles that mark the navigable channels, which scuba divers sampled along their entire submerged length (Drigo et al., 2026, p. 5). The poles are a documented seaweed habitat rather than only navigation furniture.
The lagoon is divided for this work into three sectors, southern, central and northern, set by the position and width of the three inlets that connect it to the Adriatic: Chioggia, Malamocco and Lido, running south to north (Drigo et al., 2026, p. 5). Almost every distribution statement in the survey is framed by that division. The paper names no islands and no individual barene: its 18 salt marsh sites of 2025 appear as codes with coordinates.
If you want to see the physical evidence on dry land, representative herbarium specimens from the work were deposited in the Botanical Garden collection of the University of Padua (Drigo et al., 2026, p. 14). The lagoon itself is described in the same paper as the largest transitional environment in the Mediterranean Sea and an important biodiversity hotspot, and the conclusion holds that its diversity of seaweeds, seagrasses and halophytes is considerable despite the pressures on it (Drigo et al., 2026, pp. 1, 22).
Why nearly half the seaweeds had the wrong name
Of 347 DNA samples analysed, 197, about half, produced sequences good enough to compare against reference databases. Where that comparison could be made, it contradicted the identification made by eye in the laboratory for 44.64 per cent of the seaweed samples and 29.41 per cent of the vascular plant samples (Drigo et al., 2026, p. 10). Nearly half the seaweeds had been given the wrong name from morphology alone.
The reason is partly the organisms and partly the field. Seaweeds show phenotypic plasticity, cryptic diversity and few distinctive traits, and expert taxonomists are becoming fewer, which the authors note hampers monitoring based on morphology alone (Drigo et al., 2026, p. 3). The survey used different genetic markers for different groups, then built phylogenetic trees and ran two independent species-delimitation methods rather than relying on a single database match.
Two results show why that matters. Ulva australis, reported as widespread in the lagoon by recent surveys, was not detected once, while numerous specimens came back as Ulva lacinulata, a species not formally reported there since the 19th century (Drigo et al., 2026, p. 18). And of the 35 non-indigenous species previously recorded in the lagoon, nine were re-found, among them Codium fragile and Sargassum muticum, while Vaucheria litorea was a first record, collected in 2023 and not seen again in 2024 (Drigo et al., 2026, pp. 18, 20). The authors attach a caveat: failing to detect a species in one survey does not prove it is absent from the lagoon.
