The minimum order of rotational symmetry a shape can have is 1. Some trapeziums have one line of symmetry. They are called isosceles trapeziums as they have 2 sides of an equal length like ...

In a two-dimensional periodic lattice, the highest possible symmetry is a six-fold rotational axis, but a quasicrystal structure can have a higher rotational symmetry, as shown in the example in Fig.