Glossostigma cleistanthum
(mud mat)

Nonindigenous to the U.S. Mid-Atlantic Region

Smaller than a fingertip's length, the amphibious Glossostigma cleistanthum (L.) Kuntze (Scrophulariaceae) is not your typical "aquatic invader". The tiny plant has been found at reservoirs and millponds spanning north central New Jersey and extending into southeastern Pennsylvania.

David Snyder, New Jersey Natural Heritage Program, has been following Glossostigma cleistanthum since first collecting it in Middlesex County, N.J., in 1991. In Middlesex Co. plants are abundant in patches that ring the shallow zones (~15 cm) of a spring fed impoundment.  The species continues to persist at other sites in New Jersey.  However, the author found only remnants of an earlier population at Galena Lake, Pennsylvania, in 2000.  Snyder reports G. cleistanthum remains green through the winter and suspects Canada geese as vectors in its local dispersal.  His forthcoming paper in the journal Bartonia further addresses plant migrations. Glossostigma cleistanthum likely entered the Mid-Atlantic region as an escape from aquarium culture, where plants are valued as ornamentals.

In its native, eastern hemisphere range (including New Zealand), Glossostigma cleistanthum is not a nuisance plant.  In fact, its low growing turf is considered desirable ground cover in shallow water and along wetland margins.

Potential impacts of this new species in the Mid-Atlantic region have not been investigated. It is suspected that Glossostigma cleistanthum may have a more expansive distribution than currently known.  Little effort has been made to look for it outside of New Jersey. 

Recognize Glossostigma cleistanthum as unusual, bright green patches developing on muddy substrates of littoral zones in full sun.  It's tiny leaves arise from creeping stems that grow horizontally just below the soil surface and root along the nodes.  Leaves are spatulate shaped (having linear bases with broadened tips) and reach lengths of only 1 to 2 cm.

Where the water recedes in summer months, Glossostigma cleistanthum produces minute, bell-shaped, pastel colored flowers on short stalks. Closed, self-fertilizing flowers, called cleistogams are also produced underwater and in the soil among the roots. Seeds, produced in capsules, are present in U.S. populations.

The introduced Glossostigma cleistanthum closely resembles our native Limosella (mudwort) species and may also be confused with emergent leaf forms of some members of Utricularia (bladderwort).




Sightings or specimens may be sent to Colette_Jacono@usgs.gov

Author: C.C. Jacono
March 2002
Update: March 2007

As of January 2006, Glossostigma has been identified at 19 localities in four states:  Connecticut, New Jersey, Pennsylvania, and Rhode Island.  DNA sequence analysis confirms the plants as Glossostigma cleistanthum, native to Australia and New Zealand. This plant was originally misidentified as Glossostigma diandrum.

Literature Cited: 
Les, D. H., R. S. Capers and N. P. Tippery.  2006. Introduction of Glossostigma (Phrymaceae) to North America:  A taxonomic and ecological overview. American Journal of Botany.  93(6): 927-939.

URL: http://cars.er.usgs.gov/Nonindigenous_Species/Glossostigma_cleistanthum/glossostigma_cleistanthum.html