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© E. Delbart
© E. Delbart
© E. Delbart
© E. Delbart

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© E. Delbart
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Crassula helmsii

Identity

Common name: Australian swamp stonecrop
Synonyms: Crassula recurva, Tillaea recurva, Tillaea helmsii
Origin: Australia
Plant type: Herbaceous
Life cycle: Perennial
Code of conduct: Annex I (consensus list)
Invasive status (ISEIA protocol): Black list
Main ornemental function: Plants for ponds

Description

Crassula helmsii is an aquatic or semiterrestial succulent flowering perennial herb 8-60 cm long, that grows rapidly to form an extensive lush-green carpet that floats on freshwater or may be submerged. It grows in three forms. The terrestrial form has creeping or erect stems and aerial leaves which are yellowish-green in colour and succulent in appearance. The emergent form usually grows as stands of short densely packed stems in water of 0,6m or less in depth. The submerged form grows from a basal rosette, well rooted at the base, with long sparsely leaved stems that may reach the water surface.

Spread

Sexual reproduction does not appear in Europe. It can propagate vegetatively from fragments containing a node < 5mm and has a high growth rate. Animals and birds consume Crassula helmsii and spread this way plant fragments or buoyant shoots. Fragments are also moved with mud.

Habitat

Swamp stonecrop is tolerant to a wide range of habitats. The plant colonises a wide variety of freshwater habitats with chemistry ranging from acid to alkaline, including water bodies, marshes and peat bogs. It has however not been established in fast-flowing systems. It tolerates temperatures of -6 °C to 30°C. It is frost tolerant and does not die back in winter. It requires high light levels.

Impact

Species classified A1 in Belgium. Aggressive invader in Europe. Its impact on ecosystem functioning is high. Crassula helmsii forms dense marginal and floating mats that can shade-out other water plants and result in oxygen depletion of the underlying water causing a decline in invertebrates, frogs, newts and fishes. Mats choke ponds and drainage ditches, impede water flow and adversely affect recreation activities. For more information about this species, click here

Recommendation

Do not buy nor plant this species.

Possible native alternative

Main ornemental function

Plants for ponds

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