The word star thistle (caltrop or Centaurea calcitrapa) refers to a Mediterranean herb with spiny, pink-purple flowers from the genus Centaurea[?]. It can be annual or biennial. It was natuaralized in America.
The yellow star thistle (Centaurea solstitialis) is shown in the picture below.
... a smaller extent by the slipping friction.
The device is covered by US patents 3,726,146 (1973) and 5,353,655 (1994) by L.A. Mishler and US patent 5,800,311 (1998) by ...