In Hordeum marinum two subspecies are recognized, viz. ssp. marinum , 2x and ssp. gussoneanum , 2x and 4x. The tetraploid cytotype has a more eastern distribution in the Mediterranean area than the two diploids. Crosses and meiotic data in hybrids revealed that the three cytotypes are closely related. The tetraploid ssp. gussoneanum behaves like a true alloploid but evidently has a very strong diploidizing mechanism, which prevents recombination between the genomes. The isoenzyme pattern shows differences between the cytotypes and a clinal differentiation in ssp. marinum.
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Bothmer et al. (1989) studied this question.
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