Hi Fermi
the stem of U. undulata reach about 35-40 cm (13.77-15.74 inches), U. fugax and ollivieri are a bit smaller, only 25-35 cm (9.84-13.77 inches)
the leaves of U. fugax and ollivieri are grass like, instead the ones of undulata are wavy.. i haven't any photos of U. undulata leaves, now they are resting, but you can search with google to see how beautiful they are;)