''Crassula helmsii'', known as swamp stonecrop or New Zealand pigmyweed, is an

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

or semiterrestrial species of

succulent plant In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meanin ...

in the family

Crassulaceae The Crassulaceae (, from Latin ''crassus'', thick), also known as the crassulas, the stonecrops or the orpine family, are a diverse Family (biology), family of dicotyledon angiosperms primarily characterized by succulent leaves and a form of phot ...

. Originally found in Australia and New Zealand, it has been introduced around the world. In the United Kingdom, this plant is one of five introduced invasive aquatic plants that were banned from sale from April 2014, the first ban of its kind in the country. It is on the

Global Biodiversity Information Facility The Global Biodiversity Information Facility (GBIF) is an international organisation that focuses on making scientific data on biodiversity available via the Internet using web services. The data are provided by many institutions from around th ...

Global Register of Introduced and Invasive Species Global may refer to: General *Globe, a spherical model of celestial bodies *Earth, the third planet from the Sun Entertainment * ''Global'' (Paul van Dyk album), 2003 * ''Global'' (Bunji Garlin album), 2007 * ''Global'' (Humanoid album), 198 ...

of eleven countries.

Description

The shoots are rather stiff, carrying narrow parallel-sided

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

in opposite pairs, each leaf being about . Small white

flowers Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

with four petals are produced in summer on long stalks arising from the upper leaf axils. The flowers are always above water.

Distribution

''C. helmsii'' was recorded in 2010 throughout the British Islaes, in Holland, Belgium, United States, Russia, France, Germany, Italy and Spain In Ireland, ''C. helmsii'' has been recorded on waste ground in Ireland at Howth Head, County Dublin, and at a number of sites in Northern Ireland.

Ecological aspects

The plant grows on the muddy margins of ponds where it forms carpets with 100% cover, semi-submerged in deeper water, or totally submerged with elongated stems. It does not die back in winter. It has been reported to be very tolerant to copper toxicity and to be a

hyperaccumulator A hyperaccumulator is a plant capable of growing in soil or water with high concentrations of metals, absorbing them through their roots, and concentrating extremely high levels of metals in their tissues. The metals are concentrated at levels th ...

of copper.

Cultivation

''C. helmsii'' is able to grow fully submerged in a cool-water

aquarium An aquarium (: aquariums or aquaria) is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. fishkeeping, Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquati ...

or as a submersed or marginal plant in a

pond A pond is a small, still, land-based body of water formed by pooling inside a depression (geology), depression, either naturally or artificiality, artificially. A pond is smaller than a lake and there are no official criteria distinguishing ...

. Once established it can grow vigorously and may need to be trimmed back. Schedule 9 of the UK

Wildlife and Countryside Act 1981 The Wildlife and Countryside Act 1981 (c. 69) is an act of Parliament in the United Kingdom implemented to comply with European Council Directive 79/409/EEC on the conservation of wild birds. In short, the act gives protection to native species ...

lists this plant as one that must not be caused to grow in the wild.

References

External links

''Crassula helmsii'' GBIF (images, distribution, invasive species status)

BioImages

Status in N. Ireland
includes an introduction on UK information
Flora of N. Ireland - illustrated

Ecological information
{{Taxonbar, from=Q160221 helmsii Flora of New Zealand Saxifragales of Australia Flora of New South Wales Flora of Victoria (state) Flora of Tasmania Eudicots of Western Australia Flora of South Australia Plants described in 1899 Taxa named by Thomas Kirk