Wikipedia; "In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem. The basic phyllotactic patterns are opposite, or alternate = spiral. Leaves may also be whorled if several leaves arise, or appear to arise, from the same level on a stem. This arrangement is fairly unusual on plants except for those with particularly short internodes. With an opposite leaf arrangement, two leaves arise from the stem at the same level (at the same node), on opposite sides of the stem. An opposite leaf pair can be thought of as a whorl of two leaves. With an alternate (spiral) pattern, each leaf arises at a different point (node) on the stem."
Marijuana as we all know starts off life with opposite phyllotaxy, the leaves are arranged equally on opposite sides of the stem. As it matures however that pattern changes to alternate phyllotaxy and the leaves become staggered, still on opposite sides along the stem.
Here is an example of opposite phyllotaxy...
And here is an example (if you can see it) of alternate phyllotaxy. Notice how the leaf pointed away from the camera has no leaf on the opposite side of the stem, but rather the next leaf is staggered up the plant.
Those are the two common leaf arrangements in MJ, now here's where things get messy...Whorled Phyllotaxy (as I understand it) is basically any arrangement of leaves that doesn't follow either opposite or alternate patterns. This is where the facts turn into theories however as there seems to be a shortage of definite answers with regards to the effects of whorled phyllotaxy on Marijuana, or for that matter what causes it.
From my experience I've found that whorled phyllotaxy seems like a genetic defect, mutation if you will, that either causes or is a symptom of certain stresses. From my understanding the vast majority of MJ plants affected will not be female, as has been the case with the two whorled plants I've grown myself. Whether certain factors play into the development of this condition, or it's strictly genetic I couldn't say but I ended up with two whorled plants at the same time out of seven plants from the same group of seeds. If I had to say one way or the other I would lean toward genetics playing a big role, maybe even being the sole contributor.
To be fair however I should mention that I have heard a theory that claims that whorled phyllotaxy actually becomes more common with LST, or rather the twisting of a stem. I guess the thought it that as the stem twists the soft fibres inside can get broken, crossed, or otherwise unarranged. I can't add much to this theory as I have limited experience (and reference material) but I will say that the two whorled plants I've grown were both LSTd, and that when you look at the stem in the pics it does look awfully twisted.
This is Whorled Phyllotaxy...