Micranthemum tweediei
Easier than HC 'Cuba' with similarly tiny round leaves. Plant in tiny clumps 2–3 cm apart for fastest carpet. Pearls heavily under CO₂.
Monte Carlo (Micranthemum tweediei) is a carpet / stem aquatic plant for the foreground of a planted tank. It reaches 3–5 cm under good conditions and grows at a medium rate. Light: medium to high. CO₂: recommended. Target 20–26 °C, pH 6.0–7.5, and 1–10 dGH. Substrate: Fine, nutrient-rich substrate. Propagate via cuttings spread horizontally.
Care at a glance
Easier than HC 'Cuba' with similarly tiny round leaves. Plant in tiny clumps 2–3 cm apart for fastest carpet. Pearls heavily under CO₂.
Updated 1 min read
Part of our complete guide to the planted aquarium.
Leaves yellowing, pitting, or new growth coming in pale or twisted? Work out what it’s short of in our plant deficiency guide.
The parameters that decide whether monte carlo fits in your tank.
Linderniaceae
Carpet / Stem
Foreground
Fine, nutrient-rich substrate
Cuttings spread horizontally
Boggy clearings and stream banks of Argentina
Argentina
Tank-mate safety and the species this one is documented to thrive (or fail) alongside.
Weighing it against something similar? Compare Monte Carlo head to head:
Hard-won lessons from the tank.
Plant in 1-cm clumps spaced 2 cm apart on damp substrate before filling the tank — 'dry start method' (DSM). DSM gets you a complete carpet in 3–4 weeks before water ever enters the tank. Pearling under CO₂ is one of the most rewarding aquascaping sights.
What can go wrong and how to spot it.
Failure modes, in order of how dramatic the fix is.
Stretchy growth (leggy stems): insufficient light. Pale: nitrogen. Yellowing: iron.
Hair algae attaches easily to dense growth. Stable CO₂ and proper light cycle prevent this.
The practical routine, read top to bottom.
Moderate root feeder. Root tabs help; column macro and CO₂ are important for compact dense growth.
Trim with sharp scissors every 3–4 weeks once established. Trimming forces horizontal spreading.
Where it comes from, how it behaves, and the variants you'll see at retail.
Where it lived before it came home.
See where the Monte Carlo and every other species comes from on the species world map.
Wet streambanks and pond edges in Argentina; usually grows emersed.
Almost all retail Monte Carlo is emersed-grown — leaves are slightly larger and firmer. Transitions easily to submerged form.
Tiny white flowers emersed; never flowers submerged.
The named cultivars and the lookalikes worth flagging.
Only one form sold under this name. Sometimes confused with Hemianthus callitrichoides ('HC Cuba') which has smaller, rounder leaves.
Often confused with HC Cuba — Monte Carlo has slightly larger leaves and is significantly easier. Pearlweed (Hemianthus micranthemoides) is the third commonly confused species.
Direct answers to the questions search engines and AI assistants surface most often about this species.
CO₂ requirement: recommended. Light requirement: medium to high. Under low-tech conditions the plant grows at a medium rate.
Monte Carlo (Micranthemum tweediei) needs medium to high light. Run a photoperiod of 6–8 hours; longer photoperiods invite algae unless CO₂ and dosing are dialled in.
Position: foreground. Substrate: Fine, nutrient-rich substrate It typically reaches 3–5 cm.
Propagation method: Cuttings spread horizontally. Monte Carlo is a carpet / stem plant.
Target 20–26 °C, pH 6.0–7.5, and 1–10 dGH. Flow tolerance: low to medium.
Difficulty: 3/5. Intermediate, stable parameters and a mature tank matter.
A planted tank is a system. Pair this plant with one entry from each other pillar to plan the whole scape.
