6-Needled Pines

It’s a rare event to catch a plant in the act of making a mistake. But when we do, what a curious delight. It is perhaps why we ascribe such good fortune to finding four-leaf clovers. The 4 “leaves” are actually the leaflets that together make up a compound leaf. Lots of plants have variability in the number of leaflets on a leaf. The first leaves boxelder produces in the spring tend to have 3-5 leaflets, while late season leaves have 5-7 leaflets. By the end of summer, a boxelder is a pretty even mix of leaves with 3, 5, and 7 leaflets, and I suppose a 33% chance is a pretty good reason not to consider finding a 7-leaflet boxelder good luck. But four-leaf clovers are the result of a genetic mutation and are much less common than a boxelder leaf with 7 leaflets. Your chances of finding a four-leaf clover are roughly 1 in 10,000, which seems about right for a good luck charm.

Lets say you were in a pinch and really needed to find a good luck charm. So you head to a field and start combing through the white clovers, but 1 in 10,000 isn’t going to cut it. Here are 4 ways you could make it more likely you’d find one:

1. Spend more time searching or improve the efficiency of your searching technique. The more encounters you have with clovers, the likelier it is that one will be a four-leaf clover.
2. Cheat the system and start manufacturing four-leaf clovers. This is exactly what Korean researchers are doing by irradiating plants (source). This can up your odds to 3 in 5! There are also patented varieties of red clover that reliably produces leaves with more than 3 leaflets (source).
3. Improve your odds by learning how to look. Magician turned brilliant statistician, Persi Diaconus, has shown quite clearly that the result of flipping a coin is not as random as we think. He said in an interview: “Probability isn’t a fact about the world, probability is a fact about an observer’s knowledge” (video). Since the four-leaf clover is caused by a genetic mutation, if you find one, your’re more likely to find others nearby
4. Choose a different good luck charm with better odds. Enter the white pine!

Pines can be sorted into three groups by counting the number of needles in a fascicle, or bundle. The needles in a fascicle on pine are equivalent to the leaflets that make up the leaves of white clover (or poison ivy or strawberry or white ash or elderberry). White pines are the only pines in the northeast with 5 needles in each fascicle (red, pitch, jack, and Scots pines have 2, and pitch pines have 3), or at least that’s how it’s “supposed” to be. An easy way to remember white pines is that W-H-I-T-E has 5 letters in it, a needle for each letter.

I was curious about the white pine branch after finding a second 6-needled fascicle on it. I had my tiny field assistant drag the branch in question back home to our lab. I pulled off each of the fascicles from the most recent growth of the branch (about 10″ long) and separated the fascicles by how many needles they had (see table below). Of the 170 fascicles, 51 (30%) had more than 5 needles!! There were two notable features about the branch (besides the anomalous number of needles per fascicle):

• The tip of the branch was exceptionally stout, over 1/2″ in diameter
• The branch had come from the top of the canopy

As I counted each fascicle, a clear pattern emerged: fascicles towards the tip of the branch were more likely to have more than 5 needles. It’s hard to say why exactly this pattern exists (and as with last week’s newsletter, there really isn’t much research on the topic). Wikipedia says that Scots pine, which typically have 2 needles per fascicle, can have 3 or 4 on stout branches, though it doesn’t cite a source for this or explain why.

I’ve since counted multiple branches and haven’t found any 6-needled fascicles on them. These branches were all much thinner. I’m pretty sure the odds of finding a 6-needled pine are far lower than finding a 4-leaf clover, but knowing where to look (stout branches that grow in the canopy – and get knocked to the ground in wind storms) can greatly improve your odds. I happened to be lucky that the two branches I counted on were both super stout branches.

I don’t have a definitive answer for the pattern, though I wish I did. Here are some similar situations that might hold the key:

• Unlikely: Boxelder leaves have 3-7 leaflets, but the leaves that develop later in the growing season are more likely to have 7 leaflets. It could be possible that the newest growth on the branch followed the same pattern as boxelders, but unlike boxelders, pines have determinate growth, meaning all the leaves develop at the same time early in the season.
• Unlikely: Oaks have different morphologies for leaves that grow in sun versus those in shade. Sun leaves are thicker, waxier, and are deeper cut between the lobes (i.e. they have a higher perimeter to surface area ratios), which facilitates heat dissipation. It’s possible, but this is not a genetic but an environmental response. As a result, all oak branches exhibit this pattern, while I’ve only found this on a couple of white pine branches. Not direct evidence, but the white pine anomaly is not widespread in the scientific literature, while differences in sun/shade leaves is commonly studied.
• Likely: Perhaps, as with white clovers, the anomaly is induced by UV radiation, which only occasionally produces the mutation. This could explain why I’ve found this on branches growing out at the tips in full sun.
• Likely: Or there’s another explanation that somehow is linked to the extra stoutness of the branches these oddball fascicles are found on.

I’d rather have a scientific explanation than good luck any day of the week, so I’ll keeping postulating and researching on the topic!