low st andrew's cross: low shrubby plant having yellow flowers with four petals arranged in a cross; Bermuda and southeastern United States to West Indies and eastern Mexico
st john's wort: any of numerous plants of the genus Hypericum having yellow flowers and transparently dotted leaves; traditionally gathered on St John's eve to ward off evil
pi: the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...