Wikipedia defines it as:
In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem (from Ancient Greek phýllon “leaf” and táxis “arrangement”). The process has been thought to be governed by the plant in order to minimize entropy.
So there are three types of (spiral) plant growth, and the only difference between them is how large the angle is for the next e.g. leaf or petals (which are modified leafs. So if the angle is 90 degrees its named it is denoted whorled arrangement. If the growth occurs on the opposite side of the stem of the plant - angle 180 degress - it denoted distichous plant growth. The majority of plants 80% - which is called spiral growth and has an angle in radians of:
where $\Phi$ is the Golden Ratio. So this works out to the constant value of 137.5 degrees.
The current understanding has been
Phyllotaxis, Wikipedia.
P Ball OUP 2009, Shapes. Nature’s Patterns: a tapestry in three parts