They are sympodial growers and will form handsome clumps in only a few years.
British Dictionary definitions for sympodial
noun (pl) -dia (-dɪə)
the main axis of growth in the grapevine and similar plants: a lateral branch that arises from just behind the apex of the main stem, which ceases to grow, and continues growing in the same direction as the main stem Compare monopodium
sympodial, adjective sympodially, adverb
C19: from New Latin, from syn- + Greek podion a little foot, from pous foot