Z. angustifolia is a perennial which grows on sheltered tidal mudflats, in estuaries and in coastal lagoons, usually in shallower, more turbid water than Z. marina. It is usually found on mud or muddy sands, between the half-tide and low-tide marks. Lowland.
Z. angustifolia was not recognised as a distinct species by British botanists until described as Z. hornemanniana by Tutin (1936). It was under-recorded in the 1962 Atlas, but its distribution is now better known.
Z. angustifolia is also recorded from Denmark and Sweden; it is difficult to distinguish from narrow-leaved variants of Z. marina and is not regarded as specifically distinct by Hartog (1970).
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Light (Ellenberg): 7
Moisture (Ellenberg): 12
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 8
January Mean Temperature (Celsius): 4.3
July Mean Temperature (Celsius): 15
Annual Precipitation (mm): 926
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 131
Count of 10km squares in Ireland: 27
Count of 10km squares in the Channel Isles: 6
Atlas Change Index: -0.68
Scarce Atlas Account
Zostera angustifolia (Hornem.) Reichb.
This is a marine species of mudflats and estuaries which are always well sheltered from violent waves. It is recorded from half-tide to low-tide mark, and more rarely down to 4 metres, generally in shallower but more turbid water than Z. marina (Tutin 1942), especially on muds and muddy sands (Gubbay 1988). It grows in waters of variable salinity, often about 25 g dm-3 (i.e. fairly brackish (Turin 1942)), although it has been recorded in salinities up to 42 g dm-3 (highly saline (Clapham, Tutin & Moore 1987)). It is usually found in pure stands (although rarely as extensive as Z. marina), or sometimes with the green seaweed Chaetomorpha spp. It also grows in some coastal lagoons, including The Fleet where it is accompanied by Ruppia cirrhosa, R. maritima and Zostera noltii and the charophyte Lamprothamnium papulosum.
The rhizome is perennial and long-lived, although the flowering shoots are annual. Short lengths of rhizome readily break off and are dispersed by the tide, providing the main means for establishing new colonies. It flowers in sea temperatures above 15 °C (usually around July), shedding its seeds in August and September. Germination occurs in autumn and early winter, but seedlings are always scarce, and absent in some years.
No major declines have been noted in this species, which did not suffer the wasting disease reported for Z. marina. Changes in salinity and substrate distribution as a result of estuarine ‘reclamation’ is the most serious threat at some sites.
Z. angustifolia is recorded in Europe from Denmark, Ireland and Sweden, but its distribution is imperfectly known because of confusion with Z. noltii and narrow-leaved variants of Z. marina.
Some of the mapped records for this species may well be a confusion with narrow-leaved forms of Z. marina, which can, in exposed habitats or turbulent waters, have leaves as narrow as 2 mm (Evans 1985). Stace (1991) suggests that this plant may only be a variety (var. angustifolia Hornem.) of Z. marina.
Atlas text references
1994. Scarce plants in Britain.
1942. Biological Flora of the British Isles. No. 7. Zostera genus L. (pp. 217), Zostera marina L. (pp. 217-224), Zostera hornemanniana Tutin (pp. 224-226). Journal of Ecology. 30:217-226.