This species is usually tall and erect, and more extensively rhizomatous than J. articulatus. It occurs in wet or damp habitats on acidic soils, frequently at a lower pH than is tolerated by J. articulatus, particularly in damp meadows and pastures, marshes, bogs, wet heathland, and by ditches and ponds. 0?685 m (Mangerton, S. Kerry).
The two parents frequently cohabit in areas of medium acidity, and hybrids can occur in varying quantity in a wide range of damp and wet habitats. The hybrid is sometimes commoner than either parent (as in parts of C. Wales). It is usually highly sterile, but a small proportion of flowers can produce viable seed. Lowland to 425 m at Pont Crugnant (Monts.).
A tall, tussock-forming perennial herb typically occurring in saline or brackish dune-slacks, in the uppermost levels of dry saltmarsh and on shingle banks. There is often little competing vegetation. Lowland.
This montane, rhizomatous herb occurs in rather open wet turf in marshes and flushes and by lakes and streams, usually on base-rich soil and often over limestone. It is often found with a range of other less common montane calcicoles in bryophyte-rich habitats. From 150 m near Pitlochry (E. Perth) to 880 m on the Ben Alder range (Westerness).
This dwarf, annual, spring-germinating member of the J. bufonius aggregate occurs in bare damp brackish places near the coast and sometimes inland, often with J. bufonius. It is typical of coastal mud- and sand-flats above high-water mark and of the margins of saline and brackish lakes, and is also found on bare mud and waste ground associated with inland salt-flashes and salt-workings, and on highly basic lime-waste tips. Lowland.
This very variable, erect to decumbent, clumped to extensively rhizomatous herb is found in a wide range of wet or damp habitats, both freshwater and brackish. It is characteristic of damp fields, marshes, ditches, flushes, rutted woodland rides, margins of ponds, lakes and streams and dune-slacks, avoiding only the most acid soils. 0-810 m (Great Dun Fell, Westmorland).
J. balticus usually grows in dune-slacks and other damp areas in maritime sand, mud or peat, frequently beside river estuaries, in open or closed vegetation. The plant is rhizomatous and rarely forms dense patches. It also occurs inland in N.E. Scotland on river-terraces or flood plains or in marshes. Generally sea level, but reaching 405 m on Slochd Mor (Easterness).
This short, tufted perennial herb occurs in damp rocky or gravelly places, ranging from well-watered rock faces and flushes to marshes with short open vegetation. It is confined to base-rich, but relatively competition-free, habitats in species-rich localities. From 460 m on Rum (N. Ebudes) to 1100 m in the Breadalbanes (Mid Perth) and Aonach Beag (Westerness).
An annual of habitats where the water-table is at least seasonally high and there is little competition, including the margins of ponds, lakes, streams and rivers, marshes and dune-slacks, and rarely acid bogs. It also grows around brackish lakes and on estuarine mud- and sand-flats, and is often a weed of disturbed ground, including tracks and roadsides. 0?595 m (Mangerton, S. Kerry).
These annuals are found in a wide variety of habitats which are moist or flooded in winter, and where there is some disturbance and little or no competition. This includes the edges of ponds, lakes and marshes, dune-slacks, estuaries, saltmarshes, sandy seashores, and tracks and gateways. 0?595 m (Mangerton, S. Kerry).