Mature Height2-5cm
PlacementForeground
Min. Tank20L
Water Temp20-28C

Overview

Monte Carlo (Micranthemum tweediei) is a creeping foreground plant originally collected from the Río de la Plata region of Argentina and Uruguay — not Sri Lanka. It belongs to the family Linderniaceae and was first introduced to the hobby through the Japanese aquascaping trade in the early 2000s, often appearing under the synonym Micranthemum sp. ‘Monte Carlo’. The leaves are small, round, and bright green, arranged in pairs on delicate stems that spread horizontally across the substrate. A healthy carpet produces a lush, even surface that rivals Hemianthus callitrichoides in appearance but is noticeably more forgiving of minor fluctuations in light and CO2.

Unlike HC Cuba, Monte Carlo roots readily into most nutrient-enriched substrates and doesn’t collapse as quickly when conditions dip. That said, it still demands attention to detail — neglect light levels or substrate fertility for too long and the lower layers suffocate and detach, floating loose in sheets. It’s a plant that rewards consistent maintenance over heroic rescue efforts.

Water Parameters

Temperature 20–28°C
pH 6.0–7.5
Hardness 0–15 dGH
CO2 15–30 mg/L (recommended)
Lighting Medium-High (50–80+ PAR at substrate)
Substrate Nutrient-rich aquasoil preferred

Monte Carlo tolerates a moderately wide pH band, but growth slows noticeably above 7.5, likely because CO2 availability drops at higher pH. Soft to medium-hard water works well. Very hard, alkaline tap water will stunt it over time.

Tank Placement

This is strictly a foreground carpeting plant. Plant individual tissue-culture clumps or small stem clusters 2–3cm apart across the substrate surface and allow lateral runners to knit together over four to eight weeks. Avoid burying the crowns — mount stems so the root zone touches the substrate but leaves remain above it. In tanks smaller than 40cm, Monte Carlo can fill the entire floor; in larger layouts it works best in the foreground third, kept trimmed to 2–4cm to maintain density. Trim with sharp scissors parallel to the substrate every two to three weeks once established, removing the upper 30–40% to prevent light from being blocked from lower nodes.

Light & CO2

Medium-high light is the practical minimum for a tight carpet. Below roughly 50 PAR at the substrate, internodes elongate and the plant grows upward rather than spreading horizontally, which defeats the purpose. At 70–90 PAR with injected CO2 at 20–25 mg/L, Monte Carlo will carpet across a bare aquasoil foreground in four to six weeks. Without CO2 injection, growth slows considerably — it remains possible in a well-fertilised, low-bioload tank under strong light, but expect eight to twelve weeks for the same result and a looser, less uniform mat. Liquid carbon supplements provide some benefit but are not a reliable substitute for pressurised CO2 in this application. Good surface agitation to distribute CO2 evenly across the tank is worth the effort.

Propagation

Monte Carlo propagates vegetatively and essentially does so on its own once the carpet is established — runners extend from each node and root wherever they contact the substrate. To propagate intentionally, simply trim sections of the carpet and replant them in bare substrate. Tissue-culture cups are the cleanest starting point for new tanks: rinse away the agar gel thoroughly, divide the mass into small clumps, and plant each clump individually. Avoid planting large dense clumps, as the interior suffocates before runners can establish.

Compatible Fish

Monte Carlo suits calm, small-species tanks where the carpet won’t be uprooted by digging or heavy bottom-grazing. Nano fish and gentle invertebrates that graze biofilm from the surface without disturbing roots are ideal companions. Avoid Corydoras and other substrate-sifters in tanks where a young carpet is still rooting in.

Compatible Fish

Fish that do well alongside Monte Carlo — linked where we've already covered them.

Similar Plants

Other plants with comparable care, placement, or role in a layout.

  • HC Cuba Hemianthus callitrichoides
  • Dwarf Baby Tears Hemianthus micranthemoides
  • Glossostigma Glossostigma elatinoides
  • Dwarf Hairgrass Eleocharis parvula
  • Pearl Weed Micranthemum umbrosum
  • Marsilea Hirsuta Marsilea hirsuta
  • Utricularia Graminifolia Utricularia graminifolia

Recommended Hardscape

Stone, wood, and substrate that suit how Monte Carlo is typically grown.

  • ADA Amazonia Aquasoil ADA Amazonia Aquasoil
  • Seiryu Stone Seiryu Stone
  • Manten Stone Manten Stone
  • Dragon Stone Dragon Stone
  • Controsoil Controsoil