Pearlweed

About

Every shop label reads "Hemianthus micranthemoides", and every one of them is wrong. The true micranthemoides was last collected in Virginia in 1941, is rated Possibly Extinct and was probably never in aquarium culture at all; what stands in the pot is a Florida endemic, and we publish it under its accepted name, Micranthemum glomeratum. Hemianthus glomeratus is the same plant under an older combination, so both stay in search. That identification has a hard limit worth stating: only the emersed land form flowers, and the flower is the only reliable character, so no submersed aquarium plant can be separated by eye - the correction rests on herbarium comparison, not on anything you can check at the tank. Happy, it is a bright light-green stem plant with lanceolate leaves 3-9 mm long in whorls of three or four per node, branching hard after every trim into a dense low bush. That whorl count is the whole shop-floor test: Hemianthus sp. "Amano Pearl Grass" is sold under the identical wrong label but carries only two opposite leaves per node. Dwarf baby tears (H. callitrichoides "Cuba") and Monte Carlo are true creeping carpets with tiny round leaves and are far more demanding. When conditions are not met it does not melt, it stretches: internodes lengthen, the plant climbs vertically instead of bushing out, leaves shrink and darken, and the shaded lower stems go bald with a green tuft left on top. A stand left untrimmed shades its own bottom leaves yellow until they die off, and yellow or translucent tips also point at too little light or a thin water column. Without CO2 it still grows in a well-lit tank, but often films its leaves in grey-white lime (biogenic decalcification); that is not algae and scrubbing will not shift it - lower the light or add CO2. Pot-grown stock sheds its emersed leaves over the first two or three weeks before it pushes submersed ones, which looks like death and is not; in-vitro cups are the more fragile start and do genuinely melt in a tank that is not yet cycled. The difficulty rating is contested - Tropica calls it Advanced while Flowgrow, Aquasabi and several other nurseries call it easy - and the disagreement is about form, not survival. Keeping it alive is easy; making it look like the catalogue photo takes the upper half of medium light, CO2 and a weekly trim. Without those you get a loose 30 cm bush, and left uncut in a tall tank it will run past 60 cm to the surface.

Care

Plant bunches of three or four stems deep - the roots are feeble and fresh cuttings float back up within hours unless weighted or buried further than feels right. Aim for the upper half of medium light, roughly 30-50 PAR: at 20-25 PAR it survives but stretches, and the light rating is contested, with Flowgrow and Tropica both calling it medium-to-strong where one guide calls it low-to-medium. CO2 is optional rather than mandatory - three of the sources below say so outright - but it is what stops the chalky lime film and holds the compact form. Feed the water column, not the substrate: keep NO3 around 10-50 mg/l and PO4 at 1-2 mg/l, which also gives sturdier stems. Trim the tops every week or two and replant them into the bald spots, both to keep the bush dense and to stop the stand shading its own lower leaves yellow. Never dose erythromycin or acriflavine (trypaflavine) in a tank holding it - it is unusually sensitive to both.

Frequently asked questions

What water parameters does a Pearlweed need?

Pearlweed does best at 18–28 °C (64.4–82.4 °F), pH 5–7.5 and a general hardness of 2–20 °dGH.

Where should Pearlweed be placed in the aquarium?

Pearlweed works best in the midground and reaches around 30 cm.

Is the Pearlweed suitable for beginners?

Pearlweed sits in the middle of the difficulty scale — manageable for a careful beginner who has done the reading, but it has specific needs worth researching first.

Sources

• Flowgrow Wasserpflanzen-Datenbank - Hemianthus glomeratus (Quirlblättriges Perlenkraut)
• Flowgrow Wasserpflanzen-Datenbank - Hemianthus micranthemoides (Nuttall's mudflower)
• Micranthemum glomeratum - Wikipedia
• Micranthemum micranthemoides - Wikipedia
• Flowgrow Wasserpflanzen-Datenbank - Hemianthus sp. "Amano Pearl Grass" (Smaragd-Perlenkraut)
• Aquasabi - Hemianthus glomeratus
• Tropica Aquarium Plants - Micranthemum glomeratum (048A TC)
• Tropica - Hemianthus micranthemoides, pearlweed (article)
• Shrimp and Snail Breeder - Pearlweed Care Guide: Planting, Growing, and Propagation
• Glass Box Diaries - Micranthemum glomeratum (Pearlweed) care guide