An annual or occasionally perennial herb, growing in rivers, canals, ditches, lakes and gravel-pits, typically in base-rich mesotrophic or eutrophic waters, and rarely as a terrestrial plant on wet mud. Lowland.
C. truncata appears to be increasing and spreading northwards in Britain. It has been discovered since the 1962 Atlas in Essex, Lincolnshire and Anglesey, and its range now overlaps with that of C. hermaphroditica.
Mediterranean-Atlantic element. C. truncata is also spreading northwards in mainland Europe.
Light (Ellenberg): 7
Moisture (Ellenberg): 12
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 7
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.1
July Mean Temperature (Celsius): 16.1
Annual Precipitation (mm): 719
Perennation - primary
Life Form - primary
Clonality - primary
Clonality - secondary
Count of 10km squares in Great Britain: 52
Count of 10km squares in Ireland: 1
Count of 10km squares in the Channel Isles: 2
Atlas Change Index: 0.47
Scarce Atlas Account
Callitriche truncata Guss.
C. truncata is an aquatic plant which grows totally submerged in shallow lowland waters, extending down to a depth of 1.5 metres. It is a pioneer which often appears before other species in newly created habitats such as gravel pits, or after herbicide treatment, dredging or other major management operations in ditches, drains, ponds, lakes, reservoirs, rivers and canals. It is tolerant of a range of water chemistry, but it is usually found in base-rich, mesotrophic or somewhat eutrophic waters. It is also found over a wide range of substrates, from pebbles and stones to soft organic mud. Plants are most vigorous in clear, still or very slowly flowing water but are occasionally found in sites where the water flows steadily but rather more rapidly, and can sometimes grow in turbid conditions. C. truncata often grows by itself, or with Lemna minor and Sparganium erectum in still water and Myriophyllum spicatum and Ranunculus penicillatus subsp. pseudofluitans in flowing water; Elodea canadensis is a frequent associate in both habitats.
Plants break up in autumn and float on the surface; they can overwinter as vegetative fragments. Recent observations indicate that C. truncata fruits freely at most of its British sites, producing large numbers of seeds (Barry & Wade 1986). These contrast with previous reports of populations which fruit only sparingly. Dispersal of seed is by water or possibly by wildfowl; seed fed to ducks has germinated when recovered from the faeces. Seeds have no innate dormancy, but in the wild seeds shed in autumn do not germinate until spring. Like many pioneers the species can be erratic in its appearance and sometimes reappears in a site after a long absence.
C. truncata is still present in most of the areas in which it has previously been recorded, although it is apparently extinct in Sussex, Kent, Gloucestershire and Guernsey. The reasons for these disappearances are not clear. They have been compensated for by the recent discovery of new localities, including two reservoirs and a fishing lake in Essex, a county from which it has not previously been reported.
C. truncata has a Mediterranean-Atlantic distribution. The British plant is subsp. occidentalis, which also occurs in Spain, Portugal, Belgium, France and Ireland. Subsp. truncata is found in the central and eastern Mediterranean region, and subsp. fimbriata Schotsman occurs in Russia.
For more details of the ecology of this species see Barry & Wade (1986), on which the above account is based.
C. D. Preston
Atlas text references
1986. Biological Flora of the British Isles. No. 162. Callitriche truncata Guss. Journal of Ecology. 74:289-294.
1988. The Irish Red Data Book. 1. Vascular Plants.
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
1999. A terrestrial form of Callitriche truncata Guss. subsp. occidentalis (Rouy) Braun-Blanquet (Callitrichaceae). Watsonia. 22:283-286.
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.