Hemianthus glomeratus Care Guide
Hemianthus glomeratus, known as pearl weed, is a versatile bright-green North American stem plant used as carpet, midground bush or background.
Compiled by Aquairi from published sources · Published · Updated
Overview
Hemianthus glomeratus is a small-leaved stem plant native to North America. It was long sold under the names Hemianthus micranthemoides and Micranthemum micranthemoides, but the plant common in the hobby was later identified as a distinct species, Hemianthus glomeratus. It forms airy, bright-green bushes.
Taxonomy
- Family: Linderniaceae
- Genus: Hemianthus
- Scientific name: Hemianthus glomeratus
- Former trade names: Hemianthus micranthemoides, Micranthemum micranthemoides
Habitat
Pearl weed grows in the Mid-Atlantic region of the United States, found in still waters, wet pools and ditches, including tidal rivers with gravel or sandy substrates. The true Hemianthus micranthemoides is thought by many botanists to have been extinct in its native range since around 1941.
Aquarium requirements
- Temperature: 22-28 °C (72-82 °F)
- pH: 5.5-7.5
- GH: 2-12 °dGH
- Lighting: moderate to high
- CO2: recommended (best with about 6-14 ppm)
- Placement: midground; can be trained as a carpet
- Maximum height: about 15 cm
Moderate light produces vertical growth with longer gaps between leaves, while high light keeps the plant compact and suitable for carpets. Without CO2 the leaves may form greyish-white lime deposits through biogenous decalcification.
Care and growth
Growth is fast, especially once established, and the plant requires regular trimming to stay dense and healthy. It tolerates a range of substrates including gravel, sand and aquarium soil, but benefits from added nutrients.
Propagation
Pearl weed is propagated from stem cuttings. Trimmed tops are replanted, and the plant also spreads via roots on creeping stems, forming new shoots that thicken the group.
Propagating Hemianthus glomeratus (Pearlweed)
Overview
Hemianthus glomeratus, widely sold as pearlweed, is a tall, thin stem plant carrying many small bright-green leaves. It is a fast grower and one of the hardier stem plants, which makes it forgiving to propagate. Depending on how you cut it, the same plant can be shaped into an airy upright bush or trimmed low into an easy carpet.
Propagation Method
The plant is propagated vegetatively by cuttings. The standard approach is topping: you trim the healthy tops off the stems and replant those cuttings into the substrate, where they root and continue growing. Because pearlweed branches readily, each cutting quickly thickens into its own bush.
Step-by-Step
- Select healthy stems with strong upper growth and cut the tops off cleanly with sharp scissors.
- Strip the leaves from the lowest portion of each cutting so it can be inserted without crushing foliage.
- Push each top into nutrient-rich substrate, spacing cuttings a few centimetres apart to let them bush out.
- Leave the trimmed bases in place; they will branch and produce new shoots for future cuttings.
- Replant repeatedly to fill in a midground bush or, with low trimming, a dense foreground carpet.
Conditions for Healthy Growth
Pearlweed responds best to strong lighting and benefits clearly from CO2 injection, under which it grows densely and pearls heavily. It remains hardy and relatively easy in more moderate setups, but light and CO2 are what drive the fast, compact growth that makes propagation reliable.
Trimming & Maintenance
Regular topping is both maintenance and propagation in one action. Trim the tops frequently to keep the stand dense and prevent it from growing leggy, and reuse the cuttings to expand the planting. Frequent grooming keeps light reaching the lower stems.
Common Challenges
- Skipped trims let stems stretch tall and shade out the base, thinning the bush.
- Weak light or no CO2 produces sparser, slower growth and less reliable rooting of cuttings.
- Loose cuttings can float free before rooting, so plant tops firmly and deep enough to hold.