AbstractThe influence of salinity onTypha orientalisandJuncus kraussiiwas documented in experiments on germination of seeds and on growth of seedlings and adult, rhizome‐bearing plants. Juncuswas more salt‐tolerant thanTyphaat all three life‐history stages, but salt tolerance increased with plant age for both species. Although seeds of both species germinated at 0 and 5 ppt, the germination data overestimated salt tolerance forTypha.Only the newly emerged seedlings ofJuncuswere capable of growth after removal from the 5 ppt NaCl solution to fresh water. Typhaseedlings that initiated growth at 0 ppt grew well at 5 ppt but not at 10 ppt, whileJuncusseedlings were tolerant of 10 ppt. Although the 20 ppt treatment caused high mortality ofJuncusseedlings, the 10 ppt treatment mainly reduced growth. Adult plants ofTypha,which were collected from the field, survived the 20 ppt treatment, while adultJuncussurvived the 40 ppt treatment. The presence of salt (10–40 ppt) shortened the growing season for adult, rhizome‐bearing plants of bothJuncusandTypha,with a lower maximum and earlier peak in total leaf length and maximum leaf number. Thus, the greater biomass in fresh water was achieved primarily through a longer growth period, rather than a greatly accelerated growth rate.Interactions between the two species were explored in mixed‐species culture of both seedlings and adult rhizome‐bearing plants. Interspecific interactions were present at low salinity, but results differed for seedlings and adult plants.Typhaseedlings failed to outgrowJuncusseedlings (at 5 ppt) but adult plants ofTyphaoutgrewJuncus(at 0 ppt). Relative yields (biomass in mixed/pure pots) forJuncusandTyphaseedlings were 0.85 and 0.26 at 5 ppt. Relative yields of adult plants were 0.24 forJuncusand 1.20 forTyphaat 0 ppt. For both seedlings and adults, the species that ultimately dominated the mixed‐species pots produced just as much total biomass as in pure‐species pots, even though initial planting density was half as high.Extrapolating findings to the field situation, it appears thatTyphahas a narrow regeneration niche. The indication is thatTyphacould invadeJuncusstands only following salinity reduction (allowing seed germination and early seedling growth)andafter disturbance disrupts the native vegetation. The combined conditions of prolonged low salinity and open habitat occur where street drains are cut through the salt marsh. The probability ofTyphabecoming established would be highest in such areas. vegetative expansion would follow with continued freshwater influx, as rhizome‐bearing plants gain an inte