A taxonomic nightmare comes true: phylogeny and biogeography of glassworts (Salicornia L., Chenopodiaceae)

Abstract

In this study we analysed ETS sequence data of 164 accessions belonging to 31 taxa of Salicornia, a wide‐spread, hygrohalophytic genus of succulent, annual herbs of Chenopodiaceae subfam. Salicornioideae, to investigate phylogenetic and biogeographical patterns and hypothesise about the processes that shaped them Furthermore, our aim was to understand the reasons for the notorious taxonomic difficulties in Salicornia. Salicornia probably originated during the Miocene somewhere between the Mediterranean and Central Asia from within the perennial Sarcocornia and started to diversify during Late Pliocene/Early Pleistocene. The climatic deterioration and landscape‐evolution caused by orogenetic processes probably favoured the evolution and initial diversification of this annual, strongly inbreeding lineage from the perennial Sarcocornia that shows only very limited frost tolerance. The further diversification of Salicornia was promoted by at least five intercontinental dispersal events (2× to South Africa, at least 3× to North America) and at least two independent polyploidization events resulting in rapidly expanding tetraploid lineages, both of which are able to grow in lower belts of the saltmarshes than their diploid relatives. The diploid lineages of Salicornia also show rapid and effective range expansion resulting in both widespread genotypes and multiple genotypes in a given area. Reproductive isolation through geographical isolation after dispersal, inbreeding, and comparatively young age might be responsible for the large number of only weakly differentiated lineages. The sequence data show that the taxonomic confusion in Salicornia has two major reasons: (1) in the absence of a global revision and the presence of high phenotypic plasticity, the same widespread genotypes having been given different names in different regions, and (2) striking morphological parallelism and weak morphological differentiation led to the misapplication of the same name to different genotypes in one region.

Salt tolerance of halophytes, research questions reviewed in the perspective of saline agriculture

“…The perennial salt tolerant species were geographically confined to warm temperate and Mediterranean climate zones without frost and with frequent and prolonged floodings (Kadereit et al, 2007). The geographical distribution of perennial Sarcocornia usually does not exceed the 1 • C January isotherm in the Northern Hemisphere.…”

“…It has been hypothesized that the annual life form evolved from a perennial lineage in marginal habitats with increased occurrences of frost as the driving selective force. An alternative hypothesis assumes that this evolution took place under warm climatic conditions (Kadereit et al, 2007) and that the acquired annual life form also enabled colonization of seasonally (winter) flooded areas. At the same time such adaptation to seasonal (winter) floodings also appeared to be an appropriate adaptation to habitats with severe frost.…”

“…It has been inferred from molecular phylogenetic analyses (Kadereit et al, 2007) that evolutionary diversification of extant Salicornia lineages started in the late Pliocene/early Pleistocene, about 1.8-1.4 Mya and that polyploidization played an important role. Tetraploid (2n = 36) Salicornia species originated more than once from diploid (2n = 18) Salicornia lineages.…”

“…Mya = million years ago, time estimates based on molecular clock analysis calibrated with macro fossil findings. Based on Kadereit et al (2003Kadereit et al ( , 2006Kadereit et al ( , 2007 set, seed polymorphism, high germination rates and good seedling establishment (Ungar, 1982(Ungar, , 1987.…”

“…Especially Salicornia, which diversified only 1.8-1.4 Mya has been successful in colonizing temperate and subtropical regions almost world-wide within a relatively short time. Most other genera within the Amaranthaceae are restricted to inland salt marshes, which makes long-distance dispersal more unlikely (Kadereit et al, 2007).…”