Water chestnut (Trapa natans)
Photo credit: © Sue Blanco White/Flickr

Swamp Stonecrop

(Crassula helmsii)

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Species at a Glance

Swamp stonecrop is an aquatic plant that outcompetes native species by forming dense mats in aquatic vegetation. It produces vegetative propagules that are dispersed by water, on animals, and unintentionally by humans during activities such as fishing, hiking, and restocking ponds. This species is grown as an aquarium plant and is available for sale online. It can contaminate other water plants being sold, is dispersed in water when stocking ponds with ornamental fish, can be transported to new sites by boats, and also in mud.

Similar Species

Species similar in appearance to swamp stonecrop include water pygmyweed (Crassula aquatica) as well as species of Callitriche and Elatine.

Habitat

Swamp stonecrop can grow in still and flowing water; also mud.

Distribution

Native to Australia and New Zealand, swamp stonecrop  was first found outside its native range in 1956 in a pond in Great Britain.  Presently, swamp stonecrop has not been documented as naturalized in North America. Regulation in a number of U.S. states has lead to the misconception that swamp stonecrop occurs in those states.

Environmental Impacts

This succulent plant smothers native vegetation by forming dense "carpets". Because it does not go dormant, it has a competitive advantage over native species. Dense infestations block drainage channels and cause flooding. Swamp stonecrop depletes water oxygen levels which result in population declines of fish, frogs, and invertebrates. Spread to new locations is facilitated by its ability to form new plants vegetatively from small fragments.

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Note

Information for this species profile comes from various sources including: