Population genetics and the conservation status of the threatened Iberian steppe grass Puccinellia pungens (Pau) Paunero (Poaceae)

Puccinellia pungens (Pau) Paunero is a narrowly endemic grass found in two continental saline lagoons of north‐eastern Spain. This rare plant has been classified as ‘at risk of extinction’ in several national and European catalogues of endangered species. Recent demographic studies indicate that population sizes greatly exceed several million individuals, challenging that threat category. Our genetic analysis, based on allozymes, has shown that in spite of the large population sizes, very low levels of genetic variation were found in P. pungens . Genetic variation was similar in most populations, but the largest, Gallocanta lagoon as a whole, had less variation (35% polymorphic loci, 1.4 alleles/locus, H T  = 0.038) than the more restricted Royuela range (45% polymorphic loci, 1.5 alleles/locus, H T  = 0.056), suggesting a recent population expansion of the Gallocanta populations from few founder lines. The low genetic distances among populations also suggest a recent divergence. The low genetic variation observed cannot be explained fully by eventual clonal spread and rare seedling establishment in the hypersaline environment. This low variation seems to result from extreme recent population bottlenecks as a consequence of habitat conversion to agricultural fields. In the light of our data, it seems unlikely that reinforcement of populations could increase the genetic diversity of the populations. Hence, conservation efforts should focus on avoiding further habitat loss of this endangered steppe grass species. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 269–281.