The trefoil, quatrefoil and cinquefoil are abstract forms resembling flowers or leaves. The whole is highly decorated with quatrefoil motifs, columns, trefoil motifs and bands of diapering. The fourfold version of an architectural trefoil is a quatrefoil. The heraldic "trefoil" is a stylized clover. The trefoil knot is named after the three-leaf clover (or trefoil) plant. "Oxalis" species are also known as sour grass, sour trefoil, and shamrock. A colonnade of trefoil arches and foliated capitals forms a screen to the platform. There is wild thyme, common milkwort, fairy flax, bird's-foot trefoil, autumn gentian, harebell, eyebright. Similarly, the trefoil is often combined with an equilateral triangle to form a barbed trefoil. The (2,3)-torus knot is also a trefoil knot. The lower part has a front arcade with four large arches in trefoil style. The braid group in turn is isomorphic to the knot group of the trefoil knot. The simplest nontrivial example is the (2,3)-torus knot, also known as the trefoil knot. It differs from the heraldic trefoil in being not slipped. See knot theory for an example computing the Conway polynomial of the trefoil.