The Gulf Coast of North America (GC) is a ?hot spot? of Phragmitesdiversity as several lineages (defined according to the haplotypes of their chloroplast DNA) differing in origin, genetic traits and phenotype co-exist and interbreed in this area. We analysed differences in photosynthetic characteristics among and within four haplotypes to understand if differences in gas exchange can be attributed to adaptations acquired in their native ranges. We collected rhizomes of four GC haplotypes (I2, M1, M and AI; including the phenotypes ?Land-type?, ?Delta-type?, ?EU-type? and ?Greeny-type?) and propagated them in a common controlled environment to compare photosynthesis?irradiance responses, CO₂responses, chlorophyll fluorescence, the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), specific leaf area (SLA), pigment contents, stomatal density and guard cell length. The maximum light-saturated photosynthetic rate, A_max, in the haplotype I2 (Land-type) and haplotype M1 (Delta-type) (34.3?36.1 àmol CO₂ m^?2 s^?1) was higher than that in the invasive Eurasian haplotype M (22.4 ± 2.3 àmol CO₂ m^?2s^?1). The A_max of haplotype AI (Greeny3-type) was 29.1 ± 4.0 àmol CO₂m^?2 s^?1 and did not differ from the A_max of the other haplotypes. The carboxylation rate (V_cmax) and electron transport rate (J_max) followed the same pattern as A_max. The haplotypes also differed in SLA (17.0?24.3 m²kg^?1 dry mass) and pigment content, whereas stomatal density and guard cell length, Rubisco activity and chlorophyll fluorescence did not differ significantly among haplotypes. The high photosynthetic activity and gas-exchange capacity of the two haplotypes originating in tropical Africa and the Mediterranean area (haplotypes I2 and M1) are apparently adaptations derived from their native ranges. Hence, the haplotypes can be regarded as ecotypes. However, it remains unclear how these differences relate to plant competitiveness and fitness in the GC of North America environment.