Sarcocornia fruticosa (L.) A.J. Scott is found in coastal marshes of south‐west Spain, growing under a very wide range of interstitial soil salinity from 10 mM up to nearly 1000 mM. A glasshouse experiment was designed to investigate the effect of this range of salinities on the morphology and the photosynthetic apparatus of S. fruticosa by measuring growth rate, photosynthetic and non‐photosynthetic area, atrophy of distal branch ends, water status, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. The long‐term effects of salinity on the growth of S. fruticosa were mainly determined by the extent of photosynthetic area rather than the variations in net photosynthetic rate. Photosynthetic area was reduced at 1030 mM as a result of a decrease in the length of the photosynthetic portions. This was induced by fewer internodes and, at salinities lower than 510 mM, smaller internode diameter. Net photosynthetic rate increased as the quantum efficiency of photosystem II decreased in the different salinity treatments, which means that the plant could be increasing photorespiration and/or using cyclic electron transport as additional photoprotective mechanisms. The recorded drop in net photosynthetic rate at higher salinities appeared to be due to a reduction in stomatal conductance. The results indicate that S. fruticosa is capable of tolerating very high and continued exposure to salt, showing its greatest growth rate at 510 mM NaCl.

Summary: This account reviews information on all aspects of the biology of Sarcocornia perennis that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation. Sarcocornia perennis (Miller) A.J. Scott (Salicornia perennis Miller; Salicornia radicans Sm.; Arthrocnemum [Arthrocnemon]perenne (Miller) Moss) of the European and African coasts is now considered also to include Salicornia virginica L., S. ambigua Michx. and S. gaudichaudiana Moq. of the Americas. Sarcocornia perennis is a spreading, jointed‐stemmed, halophyte that differs from the closely related Salicornia in being a shrubby perennial and in aspects of inflorescence structure. In Britain, it is found mainly on the coasts of south‐east England, on gravelly or sandy foreshores, and well‐drained sediments of tidal salt marshes. Sarcocornia perennis occurs relatively low in the tidal frame but only in well‐drained situations, as seedling establishment and long‐term survival are intolerant of highly reducing surface sediments. It has a role in the early stages of salt‐marsh succession, sometimes as the primary colonist on sandy substrates. In southern Europe, its invasion may be facilitated by the raised clonal tussocks of Spartina maritima, a primary colonist; subsequently, S. perennis dominates the tussocks and supports their rapid radial and upward growth by trapping silt. Pollen flow from the high marsh species Sarcocornia fruticosa may allow invasion by hybrids between the two species. Hybridization between the diploid S. perennis and octaploid S. fruticosa in south‐west Spain has been confirmed by analysis of random amplified DNA (RAPDs). This has also clarified the relationship between the two subspecies present there (the widely distributed ssp. perennis and the more upright, rigid Iberian endemic ssp. alpini (Lag.) Castroviejo). Sarcocornia perennis maintains low water potentials and a positive carbon balance under highly saline conditions. Salinity treatment had no effect on the efficiency of Photosystem II (Fv/Fm). Total germination was also unaffected by salinity up to 2%, although above this it was progressively inhibited; the reduction in germination at seawater concentrations was mainly osmotically enforced dormancy, which would promote dispersal by tides and currents.