Two-row

Two-row barley (Hordeum distichum), is a form of barley which is the most common grain in beer and scotch. It is also used in most whiskies. Two-row barley is the oldest form, wild barley having two-rows as well. Two-row barley has a lower protein content than six-row barley but a higher enzyme content. High protein barley is best suited for animal feed or malt that has a large adjunct content. Two-row barley is best suited for pure malts. In two-row barley only one flower is fertile.

National barley web site.