Vallisneria (Vallisneria spiralis)

Vallisneria — eelgrass or tape grass — is the rooted plant you reach for when you want a tank to fill in. It is a fast-growing, light-hungry, strap-leafed macrophyte found in rivers, lakes, and hard-water bodies the world over, and a classic Walstad-tank plant. Where the slow, shade-loving Cryptocoryne stays put as a tidy crown, Vallisneria is a coloniser: it throws out horizontal runners (stolons) that root down into open substrate and raise daughter plants, so a single crown can become a grassy thicket in a season.

Vigorous and light-demanding

Vallisneria's maximum photosynthetic rate is around three times Cryptocoryne's — still far below any alga, but brisk for a rooted plant, fast enough that in nutrient-rich, well-lit conditions a crown can put up several daughters a month. The model folds that runner-based spread into the elevated growth rate rather than tracking each daughter plant separately. The catch is that this pace needs light: Vallisneria wants roughly twice the irradiance Cryptocoryne is content with. In a dim Walstad tank it will still outgrow the Crypt but sits below its own optimum; given bright light it surges and can shade out more retiring competitors.

It is also more tolerant of hard, alkaline water than Cryptocoryne, comfortable at higher pH before it begins to stress — a direct reflection of the hard rivers and lakes it comes from.

A bicarbonate plant

The trait that defines Vallisneria's chemistry is its carbon-concentrating mechanism: it is the strongest bicarbonate user among the model's rooted plants. In hard water at high pH, where dissolved carbon dioxide has all but vanished but bicarbonate is plentiful, Vallisneria actively strips bicarbonate from solution and releases hydroxide in exchange, visibly driving the local pH upward as it photosynthesises (Prins & Elzenga 1989). This is why it keeps growing through the afternoon CO₂ crash that would stall a strict CO₂-only plant: even when daytime drawdown empties the water of free carbon dioxide, the bicarbonate route carries it across the whole normal aquarium pH range. It can take a supplemental sip of carbon dioxide from sediment pore water through its roots as well, but it depends on that far less than Cryptocoryne does — the bicarbonate mechanism already covers most of its carbon demand straight from the water column.

Feeding from both worlds

Vallisneria splits its nutrient gathering more evenly than Cryptocoryne. A little over half its capacity comes from pore water through high-affinity root transporters — which still give it the tightest grip on dilute sediment nutrients of any plant here — and the rest from the water column through its leaves. That balance means it establishes faster in a well-fertilised water column and is less utterly dependent on a rich buried substrate than the soil-mining Crypt, so it is a better fit for a tank whose fertility is in the water rather than the mud.

Casting a canopy

A mature Vallisneria bed is tall: strap leaves run from the substrate clear to the surface, and a dense stand intercepts a real fraction of the incoming light before it can reach the algae and benthic surfaces below. As the bed thickens, that shade progressively dims the water column and the substrate beneath it. Combined with the way its roots intercept nutrients diffusing up through the sediment — quietly starving the open water of the pore-derived nitrogen and phosphorus that would otherwise feed an algal bloom — this shading is one of the levers that tips a tank from algae-dominated toward the clear-water, plant-dominated stable state that healthy planted aquaria settle into (Scheffer et al. 1993; Walstad 1999). Short rosette plants like Cryptocoryne, whose leaves stay low, cast no comparable shadow.

Cryptocoryne versus Vallisneria at a glance

The model's two rooted plants occupy complementary niches and coexist stably — the shade-tolerant slow burner alongside the bright, vigorous coloniser:

The exact growth rates, light and bicarbonate half-saturations, root-versus-water uptake split, canopy coefficients, and pH thresholds behind this contrast are tabulated in the Parameter Reference.

Further reading

• Cryptocoryne — the slow, shade-tolerant, CO₂-only rooted plant that partners with Vallisneria
• Macrophytes: Aquatic Plants — the shoot/root split, dual nutrient sources, and canopy-shading mechanics in full
• Producers — how all the algae and plants fit together
• Iron Cycle — how rooted plants mine iron and phosphorus from the sediment, and the iron-plaque chemistry at the root surface
• Soil and Pore Water — the sediment pore pools and root interception that starve the water column of algal fuel
• Parameter Reference — every rate, half-saturation, and threshold behind this page, with citations

Key references

• Barko, J.W. & Smart, R.M. (1985). Laboratory study of sediment-related factors affecting aquatic plant development. Ecological Monographs 55, 63–78.
• Carignan, R. & Kalff, J. (1980). Phosphorus sources for aquatic weeds: water or sediments? Science 207, 987–989.
• Prins, H.B.A. & Elzenga, J.T.M. (1989). Bicarbonate utilization, pH polarity and proton extrusion in the aquatic angiosperm Vallisneria spiralis. Aquatic Botany 34, 59–83.
• Scheffer, M., Hosper, S.H., Meijer, M.-L., Moss, B. & Jeppesen, E. (1993). Alternative equilibria in shallow lakes. Trends in Ecology & Evolution 8, 275–279.
• Smits, A.J.M., van Avesaath, P.H. & van der Velde, G. (1990). Carbonate chemistry and the availability of CO₂ and HCO₃⁻ for Potamogeton pectinatus in sediments. Aquatic Botany 38, 345–362.
• Walstad, D.L. (1999). Ecology of the Planted Aquarium. Echinodorus Publishing.