This species occurs in mesotrophic lakes, canals and gravel-pits. It is usually annual, although some populations may perennate. 0-390 m at Drumore Loch (E. Perth).
C. hermaphroditica was under-recorded in the 1962 Atlas. There is no evidence of a general decline, though it has been lost from some sites, possibly because of deteriorating water quality. However, recent records from gravel-pits in Lincolnshire and canals in the Midlands suggest that it may be spreading in those areas. It is morphologically variable; populations in our area include at least three forms.
Circumpolar Boreal-montane element.
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Light (Ellenberg): 7
Moisture (Ellenberg): 12
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 1
January Mean Temperature (Celsius): 3.1
July Mean Temperature (Celsius): 13.7
Annual Precipitation (mm): 1120
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 392
Count of 10km squares in Ireland: 115
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.21
Scarce Atlas Account
Callitriche hermaphroditica L.
Status: not scarce
This aquatic species usually grows on silty substrates in mesotrophic or eutrophic lakes. It can be found in shallow water at the edges of sheltered lakes, but in more exposed sites it is confined to deeper water. Species such as Myriophyllum alterniflorum, Potamogeton gramineus, P. x nitens and Nitella flexilis are often found in its more mesotrophic localities, where less frequent associates include Najas flexilis and Potamogeton praelongus. Unlike these scarce species, C. hermaphroditica is also found in abundance in some eutrophic waters, such as the Anglesey lakes, where it can be found with Potamogeton crispus, P. pusillus and Zannichellia palustris. C. hermaphroditica has also been recorded as a colonist of canals and flooded gravel pits. It is a predominantly lowland species, recorded up to 350 metres (Kingside Loch) and 380 metres (Malham Tarn, where its occurrence may have been transient). A record from 425 metres in Perthshire (White 1898) requires confirmation and one from 915 metres in Inverness-shire (McCallum Webster 1978) is erroneous.
C. hermaphroditica is a shallow-rooted annual. The flowers are submerged and pollinated under water. Plants fruit freely. Fruiting plants are often uprooted by autumn winds. Little is known about its germination requirements.
Like many aquatics, C. hermaphroditica was under-recorded in the Atlas of the British Flora (Perring & Walters 1962) and it is difficult to assess any changes in its distribution. There is no evidence to suggest that it has declined, and its tolerance of eutrophication suggests that it is unlikely to be threatened by changes in water quality. In 1985 it was discovered in gravel pits in Lincolnshire, a significant extension of its British distribution.
It is a widespread circumboreal species, occurring in Europe, Asia and North America. In Europe it has a predominantly northern distribution, extending south as far the British Isles, northern Germany and Rumania; it is absent from the Alps.
Although a relatively distinct species, C. hermaphroditica has sometimes been confused with C. hamulata. Many of the records cited by McCallum Webster (1978) are erroneous.
C. D. Preston
Atlas text references
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
1978. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 2. 2 vols.
1997. Aquatic plants in Britain and Ireland.
1967. Les Callitriches: espèces de France et taxa nouveaux d'Europe.
1994. Scarce plants in Britain.