Holly-leaved naiad (Najas marina)

French: Naja de Marine
GenusNajas (1)
SizeLeaf width (including teeth): 1 - 6 mm (2)
Leaf length: 1.0 - 4.5 cm (2)
Fruit size: 4.0 - 6.0 x 1.5 - 3.0 mm (2)

The holly-leaved naiad is classified as Least Concern (LC) on the IUCN Red List (1). It is classified as Vulnerable in Great Britain, and is fully protected in the UK by Schedule 8 of the Wildlife and Countryside Act 1981 (3).

The holly-leaved naiad (Najas marina) is an aquatic plant (3) that has tough narrow leaves on forked, brittle stems. Both the leaves and the stems have spiky projections; these occur particularly towards the tip of the stem (4). The flowers are highly inconspicuous, and the fruit, which lacks a stalk, is fleshy (2).

This species is found in the UK in just three of the Norfolk Broads (5). The holly-leaved naiad is also known from both temperate and tropical areas including Europe, Asia, Australia, Africa, and North and Central America (3). In Europe the species is classified as Vulnerable (3).

The holly-leaved naiad prefers clear, unpolluted water in fens and reedbeds (5), and shows a preference for sheltered areas (3). It typically grows at depths of between 0.5 and 1.5 millimetres (3) often in slightly brackish water (2).

The holly-leaved naiad occurs as either an annual or a short-lived perennial, and flowers in July and August (3). Male plants were only recently discovered in the UK, and it was previously thought that the plant could reproduce without cross-fertilisation (3).

The main threats to the holly-leaved naiad include nutrient enrichment of water bodies following sewage inputs and agricultural run-off, and boat traffic, which causes pollution and turbulence (5).

The holly-leaved naiad is a UK Biodiversity Action Plan priority species. The Species Action Plan produced to guide the conservation of the species aims to maintain the current populations, and restore the plant to at least five adjoining waterways before the year 2004 (5). All three of the known sites are Sites of Special Scientific Interest (SSSIs), and the Royal Botanic Gardens, Kew are investigating seed-storage techniques suitable for the species (5).

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (June, 2011)
  2. Stace, C. (1991) New Flora of the British Isles. Cambridge University Press, Cambridge.
  3. Wigginton, M.J. (1999) British Red Data Books 1: Vascular Plants. 3rd Edition. JNCC, Peterborough.
  4. Clapham, A.R., Tutin, T.G. and Moore, D.M. (1987) Flora of the British Isles. 3rd Edition. Cambridge University Press, Cambridge.
  5. UK Biodiversity Species Action Plan (November, 2001)