Lysimachia nummularia - Immersed Potted Plant

Lysimachia nummularia (often sold as "Moneywort" or "Creeping Jenny") is a creeping stem plant with small round leaves that can be grown submerged, but is naturally a marginal/bog species. In aquaria it works as a cool-water accent or background bush, but is less stable long-term in warm, tropical tanks. Best used in temperate or unheated aquaria, or at the waterline in open-top/river-style layouts.

Origin

• Region: Europe and Western Asia

• Habitat: Damp meadows, pond and stream margins, often partly submerged or periodically flooded.

Physical characteristics

• Growth form: Creeping, opposite-leaved stems that root at the nodes.

• Leaf shape & size: Round to oval leaves, about 0.5–1.5 cm across.

• Colour: Medium to deep green (non-aurea).

• Height in aquaria: Usually 10–20 cm tall submerged, stems can be longer and trailing.

Aquarium requirements

Difficulty

• Level: Moderate (because it is not a true long-term tropical aquatic plant).

• Best results in cooler, well-oxygenated aquaria.

Lighting

• Requirement: Medium light; medium–high gives denser, tighter growth.

• Low light → longer internodes, thin and leggy.

CO₂

• Demand: Low–medium.

• Will grow without injected CO₂, but responds with stronger growth and better health if moderate CO₂ (~10–20 mg/L) is provided.

Nutrients & substrate

• Substrate: Standard sand or fine gravel is fine; it is mainly a water-column feeder.

• Fertilisation:

  • Regular liquid fertiliser (NPK + traces) helpful.

  • Root tabs optional; more important is good overall nutrition and clean water.

Water parameters (for aquaria)

• Temperature: Best 16–22 °C; tolerates about 10–24 °C.

  • Long-term health in 26–28 °C tropical tanks is unreliable.

• pH: ~6.0–7.5

• GH: Soft to moderately hard water tolerated.

• Flow: Gentle to moderate; fine stems dislike very strong, direct current.

Planting & spacing

• Plant individual stems or small bunches a few centimetres apart.

• Do not bury leaves; only the lower nodes and roots go into the substrate.

• Works as a mid- to background plant, or as a creeping accent among rocks and wood.

Propagation

• Very easy via stem cuttings:

  • Cut healthy tops 5–10 cm long and replant.

  • Horizontal stems will root at nodes; you can cut between rooted nodes and plant them separately.

Maintenance

Trimming

• Regular trimming prevents legginess and encourages side shoots:

  • Top cutting: Trim tall stems and replant the best tops; remove old bases if they are bare.

  • Pinch side shoots to create a bushy clump.

General care

• Prefers stable, cool, clean water.

• Good surface agitation and oxygenation help, especially in unheated tanks.

Aquascaping use

• Adds a soft, round-leaved texture that contrasts nicely with grasses and fine stems.

• Great in:

  • Temperate community tanks (white cloud mountain minnows, temperate danios, etc.).

  • River / stream-style layouts with stones, wood and cooler flow.

• Can be used at the waterline in open-top aquaria, letting some stems grow emersed while roots remain submerged.

Companion compatibility

With fish & invertebrates

• Safe for: Most community fish, shrimp and snails.

• Delicate stems can be damaged or uprooted by large, boisterous fish or diggers (big cichlids, goldfish, large loaches).

With other plants

• Spreads moderately; not as aggressive as some true aquatics, but can overshadow delicate foreground plants if allowed to sprawl unchecked.

Lifecycle & submerged behaviour

• Naturally a perennial marginal plant.

• In aquaria:

  • Adapts to submerged growth but may decline over time if kept warm and shaded.

  • Performs best when at least some parts can grow emersed, or in cool-water tanks.

Common issues & diagnostics

• Leggy, sparse stems:

  • Cause: Low light or shading.

  • Fix: Increase light, trim tops and replant to reset.

• Leaves melting/rotting at higher temperatures:

  • Cause: Kept like a tropical stem in 26–28 °C for long periods.

  • Fix: Use in cooler tanks, give some emersed access, or choose a dedicated tropical stem as alternative.

• Stunted, pale new growth:

  • Cause: Nutrient deficiency (often micronutrients) or unstable CO₂ under strong light.

  • Fix: Improve fertilisation regime and/or stabilize CO₂ if injected.

Special features / Benefits

• Attractive round-leaf alternative to the usual narrow-leaved stems.

• Excellent transition plant between hardscape and other stems in cool-water aquaria.

• Can be integrated between aquarium and emergent planting in open-top or riparium-style tanks.

Origin
Country or continent where a plant is the most common. Cultivars arise or are bred in cultivation.

Growth Rate
Growth rate of the plant compared to other aquatic plants.

Height
Average height (cm) of the plant after two months in the tank.

Light Demand
The average or medium light demand of an aquarium plant is 0.5 W/L.

CO2 Demand
A medium need in CO2 is 6-14 mg/L. A high demand in CO2 is approx. 15-25 mg/L.