Pattern of morphological variation of Salicornia in north Europe

Abstract

Among the few available morphological traits in the genus Salicornia L. (Amaranthaceae/Chenopodiaceae), most are extremely variable within species probably due to high levels of plasticity. In addition, identifying Salicornia taxa is further complicated by that these plants lose many of their diagnostic characters upon drying. Morphological studies of fresh (or liquid preserved) specimens is thus important in taxonomical studies. The objective of this study was a numerical morphological analyses of Salicornia populations in the Nordic countries and an adjacent Russian region with the aim to ascertain whether taxonomic division of this genus based on morphology is feasible. In all, 666 plants were collected for morphometric measurements from 31 localities and 52 populations or subpopulations of the North Sea coasts, Danish straits, Baltic Sea, the Norwegian Sea, Barents Sea, and the White Sea areas. For practical reasons, part of the samples was studied fresh, and part preserved in FAA pending measurements. Data were analyzed by principal component analysis (PCA) and hierarchical cluster analysis. The main taxonomical division was found between the diploid S. europaea s.l. and the tetraploid S. procumbens Sm., and was mainly based on fertile segment and flower morphology characteristics. Data also show ecological differences: diploids inhabit the upper part of salt marshes, whereas tetraploids grow in the hydrolittoral zone and are restricted to areas of regular tidal influence. It was not possible to make a morphological distinction between the two cryptic diploid species S. europaea s.s. and S. perennans Willd. in the present study. North Norwegian S. europaea clearly deviated from more southern populations, but taxonomical conclusions based only on morphology were avoided. In contrast, the division of S. procumbens into two geographical races/subspecies, the southern subsp. procumbens and the northern subsp. pojarkovae was supported.