Hygrophila polysperma: grower data and its US noxious weed status

What the grower data says

Tropica describes Hygrophila polysperma as one of the hardiest aquarium plants available and particularly good for beginners, because it grows in almost all conditions ^[1]. Its ratings are easy difficulty with low light and low CO2 demand; the growth-rate field is blank on Tropica’s page, so that rating is not published, but the description is clear that the plant “normally grows so fast” that it has to be kept from crowding out other plants ^[1]. Stems reach 25–40 cm and 4–8 cm across.

The description also explains why it looks different from tank to tank: leaf shape and color vary considerably, depending partly on the light it receives ^[1]. Tropica sells a pink-veined form, ‘Rosanervig’, which it rates easy with medium growth, low light and medium CO2 demand ^[2].

Placement and planting

Neither grower page cited here names a position in the tank. With stems of 25–40 cm ^[1] it is taller than typical foreground plants. Tropica’s maintenance advice is to pinch out the shoots regularly ^[1], which keeps the group bushy and stops it shading lower plants.

Growth and propagation

Two features make this plant easy to propagate and hard to contain. Cut shoots can be replanted, as with other stem plants, and Tropica notes that leaves lying on the water surface form small new plants ^[1]. Any fragment that drifts in the tank, or leaves it, can become a new plant. That is useful in an aquarium and is exactly the trait that makes the species a concern outdoors.

Legal status

Hygrophila polysperma is designated a federal noxious weed in the United States. The regulation, 7 CFR 360.200, lists it among the aquatic and wetland weeds as “Hygrophila polysperma T. Anderson (Miramar weed)” ^[3]. A footnote to the same section explains that a species-level listing includes all its subspecies, varieties and forms ^[3]. The regulation exists to prevent the introduction and spread of the listed plants; state rules may add further restrictions. Check the current federal and state rules before buying, trading or disposing of this plant, and never put trimmings into drains, ponds or waterways. See invasive aquarium plants and safe disposal.

Names and taxonomy

The World Checklist of Vascular Plants accepts Hygrophila polysperma (Roxb.) T.Anderson, in the acanthus family Acanthaceae, with Justicia polysperma Roxb. as the original name ^[4]. Its native range runs from Afghanistan and Pakistan across India, the Himalaya and Sri Lanka to southern China, Taiwan, Myanmar, Thailand, Vietnam and Malaya ^{[4, 5]}.

The same record lists where it has been introduced: Alabama, Florida, Mississippi, South Carolina, Texas and Virginia in the United States, north-east Mexico, Germany, Poland and Japan ^[4]. Tropica’s grower data gives “Asia”, and its description “South-East Asia” ^[1], both inside the native range.