Pinus

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Pine Cones Are Like Hangars for Pine Tree Seeds

Over the past year I’ve written about the making of pine tar and the drinking of pine needle tea. But why stop there? Pines are a fascinating group of plants, worthy of myriad more posts, and so my exploration into the genus continues with pine cones and the seeds they bear.

Pines are conifers and, more broadly, gymnosperms. They are distinct from angiosperms (i.e. flowering plants), with the most obvious distinction being that they don’t make flowers. Since they are flowerless, they are also fruitless, as fruits are seed-bearing structures formed from the ovary or ovaries of flowering plants. Pines do make seeds though, and, as in angiosperms, pollen is transported from a “male” organ to a “female” organ in order for seeds to form. Rather than being housed in a fruit, the seeds are essentially left out in the open, which is why the term “naked seeds” is frequently used in reference to gymnosperms.

seed cone of Scots pine (Pinus sylvestris ‘Glauca Nana’)

In the case of pines and other conifers, the seeds may be naked, but they’re not necessarily homeless. They have the protection of cones, which is where the female reproductive organs are located. Male, pollen cones are separate structures and are smaller and less persistent than the cones that house the seeds. A cone, also known as a strobilus, is a modified branch. A series of scales grow in a spiral formation along the length of the branch, giving the cone its shape. On the inside of these scales is where the seeds form, two per scale. First they are egg cells, and then, after pollination and a period of maturation, they become seeds. The scales protect them throughout the process and then release them when the time is right.

With more than 120 species in the genus Pinus, there is great diversity in the size, shape, and appearance of pine cones. While at first glance they don’t appear all that different from one another, the cones of each species have unique characteristics that can help one identify the pine they fell from without ever having to see the tree. Pine cones are also distinct from the cones of other conifers. For one, pine cones take at least two or, in some cases, three years to reach maturity, whereas the cones of other conifers develop viable seeds in a single year. Pine cones are also known to remain on the tree for several years even after the seeds are mature – in some species up to 10 years or more – and they don’t always part with their seeds easily. Lodgepole pines (Pinus contorta) require high temperatures to melt the resin that holds their scales closed, the cones of jack pine (P. banksiana) generally only open in the presence of fire, and the seeds of whitebark pine (P. albicaulis) are extracted with the aid of birds (like Clark’s nutcracker) and other animals.

immature seed cone of lodgepole pine (Pinus contorta)

Every pine cone is special in its own right, but some stand out in particular. The largest and heaviest pine cones are found on Coulter pine (P. coulteri), measuring up to 15 inches long and weighing as much as 11 pounds with scales that come to a sharp point. It’s understandable why the falling cones of this species are frequently referred to as widowmakers. Longer cones, but perhaps less dangerous, are found on sugar pine (P. lambertiana). The tallest trees in the genus, the cones of sugar pine consistently reach 10 to 20 inches long and sometimes longer.

Pine tree seeds are a food source for numerous animals, including humans. Most are so small they aren’t worth bothering with, however, several species have seeds that are quite large and worth harvesting. Most commercially grown pine nuts come from stone pine (P. pinea) and Korean pine (P. koraiensis). In North America, a wild source for pine nuts is found in the pinyon pines, which have a long history of being harvested and eaten by humans.

immature seed cone of ponderosa pine (Pinus ponderosa)

The seeds of many pines come equipped with little wings called samaras, which aid them in their dispersal. Upon maturity, pine cone scales open and release the seeds. Like little airplanes leaving the hangar, the seeds take flight. Wind dispersal is not an effective means of dispersal for all pines though. A study published in Oikos found that seeds weighing more than 90 milligrams are not dispersed as well by wind as lighter seeds are. When it comes to long distance dispersal, heavier seeds are more dependent on animals like birds and rodents, and some pines rely exclusively on their services. The author of the study, Craig Benkman, notes that “bird-dispersed pines have proportionately thinner seed coats than wind-dispersed pines,” which he points out in reference to Japanese stone pine (P. pumila) and limber pine (P. flexilis), whose seeds weigh around 90 milligrams yet rely mostly on birds for dispersal. Benkman suspects that the seeds of these two species “would probably weigh over 100 milligrams if they had seed coats of comparable thickness as wind-dispersed seeds.”

Whitebark pine, as mentioned above, holds tightly to its seeds. Hungry animals must pry them out, which they do. Pine seeds are highly nutritious and supplement the diets of a wide range of wildlife. Some of the animals that eat the seeds also cache them for later. Clark’s nutcrackers are particularly diligent hoarders, harvesting thousands more seeds than they can possibly consume and depositing them in small numbers in locations suitable for sprouting.

Even large seeds that naturally fall from their cones have a chance to be dispersed further. As the seeds become concentrated at the base of the tree, ground-foraging rodents gather them up and cache them in another location, which Benkman refers to as secondary seed dispersal.

Particularly in pine species with wind dispersed seeds, what the weather is like helps determine when the hangar door will open to release the flying seeds. When it is wet and rainy, the scales of pine cones close up. The seeds wouldn’t get very far in the rain anyway, so why bother? When warm, dry conditions return, the scales open back up and the seeds are free to fly again. You can even watch this in action in the comfort of your own home by following the instructions layed out in this “seasonal science project.”

immature seed cones of limber pine (Pinus flexilis)

mature seed cones of limber pine (Pinus flexilis)

Further Reading:

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Photos of pine cones were taken at Idaho Botanical Garden in Boise, Idaho

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Tea Time: Pine Needle Teas

Temperatures are cooling in the northern hemisphere, which has me looking forward to drinking more hot tea. Making tea is a simple way to try edible plants you’ve never tried before, which I have demonstrated in past posts about pineapple weed and chicory. Believe it or not, I’m interested in trying teas made from other plants besides weeds, which has led me to start a new series of posts. It’s tea time!

When you think of a pine tree, your first thought probably isn’t, “Hey, I could make some tea out of that.” Sure, pine trees are known for their pleasant scent; however, do you really want a tea that tastes like a Christmas tree or smells like the cleanser you mop your floors with? A mouthful of pine needles just doesn’t sound that appetizing. Luckily, tea made with pine needles has a considerably milder aroma and flavor than you might initially expect.

the needles of Japanese red pine (Pinus densiflora)

Pines actually have a number of edible parts. Young, male cones can be boiled and eaten, pine pollen can be used in a number of ways, and roasted pine seeds (also known as pine nuts) are commonly consumed and used to make things like pesto and hummus. In addition, the inner bark, sap, and resin all have a history of being used as food and medicine. So, why not the needles?

However, it should be noted that turpentine comes from pine trees, which is quite toxic if ingested or used improperly. Turpentine is made by distilling the sap and resins found in pine trees. The high concentration of the chemical compounds found in these products is what results in turpentine’s toxicity.

Another caveat is that the word “pine” is used as a common name for a few species that are not in the genus Pinus and thus are not true pines. Also, coniferous trees and shrubs are frequently referred to as or thought of as pines by people who aren’t in the know. Hence, always make sure that you positively identify any and all plant species before you consume them. Additionally, various sources advise avoiding the consumption of ponderosa pine (Pinus ponderosa) and a handful of other pines, which may in fact be perfectly safe in moderation, but the counsel is worth keeping in mind.

To drill these points home, consider this passage from The North American Guide to Common Poisonous Plants and Mushrooms:

Most [conifers] would be too strong-tasting and unpalatable to eat, but many can be used safely as flavorings or to make beverages and medicinal teas, as long as they are taken in moderation and in low concentrations. Exceptions are the yews (Taxus spp.), which are highly toxic, and ponderosa pine, a tree of dry western forests with long needles usually in clusters of three. Some indigenous people ate the inner bark and seeds of this pine, but they knew that pregnant women should not chew on the buds or needles because it would cause a miscarriage. Eating the foliage of this pine is known to cause abortion in late-term pregnant cattle and other livestock due to the presence of isocupressic acid, which has also been found in lodgepole pine (P. contorta) and Jeffrey pine (P. jeffreyi). Other pines, such as loblolly pine (P. taeda) of the southeastern United States should also be regarded with caution.

I chose to make tea from the needles of two species that have a long history of being used for this purpose: Korean or Japanese red pine (Pinus densiflora) and eastern white pine (Pinus strobus). Pinus densiflora occurs in Korea and Japan, as well as parts of China and Russia, and has been given the name red pine thanks to its attractive red-orange bark. It produces needles in bundles of two and is a member of the subgenus Pinus, also known as the hard pines. Pinus strobus occurs mainly in the northeastern corner of the United States and the southeastern corner of Canada. It’s a member of the soft pines (subgenus Strobus) and produces needles in bundles of five. Both of these trees (and various cultivars of them) are commonly grown ornamentally outside of their native ranges.

the bark of Japanese red pine (Pinus densiflora)

To make the tea, I collected a handful of needles, chopped them in half or thirds and steeped them in hot water. Various sources that I read said not to boil the needles. The teas had a mild pine scent and a light citrusy flavor. I first made a tea from eastern white pine needles and accidentally added too much water. On my second try, using Korean red pine needles, I got the ratio better, and the tea didn’t taste so watered down. Some people add honey to pine needle tea, which I didn’t try this time around because I wanted to experience the taste of the needles. However, I think honey would be a nice addition.

Younger needles are said to be better than older needles for making tea, and I imagine that the time of year that the needles are harvested could have an impact on the flavor. The age of the needles likely determines, in part, its amount of vitamin C as well. Pine needle tea is said to be high in Vitamin C, which is another reason to give it a try.

the needles of eastern white pine (Pinus strobus)

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From Pine Tree to Pine Tar (and a bit about baseball)

Scots pine (Pinus sylvestris) is a Eurasian native, distributed across Europe into Eastern Siberia. It is the national tree of Scotland, and the only native pine in northern Europe. Human activity has pushed native populations to extinction; while, at the same time, appreciation for this tree has led to widespread introduction in other parts of the world. Like other pines, humans and Scots pine have a long relationship going back millennia. Pines are incredibly useful trees, which explains both the overexploitation and mass planting of Scots pine.

Scots pine (Pinus sylvestris) via wikimedia commons

In Sweden and other Scandinavian countries, Scots pine not only has a long history of being used as a building material, but also for producing pine tar. As the name suggests, pine tar is a dark, sticky substance extracted from pine wood. Wood tar production dates back centuries and has been made from a number of tree species, including pines and other conifers as well as deciduous trees like birch and beech. Wood tar has myriad uses – as an ingredient in soaps, shampoos, and cosmetics; as medicine; as a food additive; as waterproofing for ships, roofs, and ropes; in hoof care products for horses. It’s no wonder that as demand for pine tar increased in Scandinavia, it became a cash crop for peasants, earning it the nickname “peasant tar.”

Pine tar soap – a decent soap if you can tolerate the intense smell. Regarding the smell of pine tar, Theodore Kaye writes, “The aroma produces reactions that are as strong as the scent; few people are ambivalent about its distinctive smell.”

A study published in the Journal of Archaeological Science examines small and large funnel-shaped pits in Sweden determined to be used for making pine tar. The smaller pits date back to between 240 – 540 AD, the Late Roman Iron Age. They would have been used by Swedes living in small scale settlements. The larger pits date back to 680 – 1160 AD and signify a shift towards large scale production during the Viking Age. As the centuries proceeded, Sweden became a major exporter of pine tar. Their product set the standard. Even today “Stockholm Tar” refers to pine tar of the highest quality.

As Europeans colonized North America, they were introduced to several new pine tree species from which to extract pine tar, including longleaf pine (Pinus palustris), a southeastern native with exceptionally long needles. Pine tar production was especially prolific in the southeastern states, thanks in part to the abundance of longleaf pine and others. North and South Carolina were dominating production by the 1800’s, which helps explain North Carolina’s nickname, The Tar Heel State.

Extracting pine tar from pine wood is fairly simple. The process is called destructive distillation. Pine wood is placed in a contained, oxygen-free environment and subjected to high heat. As the pine tar is released from the wood, the wood turns to charcoal. This is what was happening in the small and large funnel-shaped pits discussed earlier. Root pieces and stumps of Scots pine were placed into the pits. Brush wood was piled on top and then set on fire. As the brush burned, the pine wood below carbonized, and pine tar collected at the bottom of the pit. In larger pits, the pine tar was piped out and deposited into a barrel – a set up known as a pine tar dale.

pine tar dale illustration

Modern production of pine tar is done in kilns (or in laboratories). The concept is the same – wood is enclosed in the kiln, heat is applied, and pine tar drips from the bottom of the kiln. Heartwood, also known as fatwood, is the best part of the pine tree for making pine tar, particularly the heartwood of old stumps. Making pine tar is such a simple process that anyone can do it, and there are numerous tutorials available online.

My familiarity with pine tar comes from being a baseball fan. Pine tar is a useful, albeit controversial, substance in this sport. Batters have a variety of means to help them get a better grip on the bat in order to improve their hitting. Rubbing pine tar on the bat handle is one of them. However, according to Major League Baseball rules, anything applied to, adhered to, or wrapped around the bat to help with grip is not allowed past the bottom 18 inches of the bat. Pine tar is allowed on the bat handle, but if applied past that 18 inches mark, the bat becomes illegal.

pine tar stick for baseball bat handles

This rule goes mostly ignored; unless, of course, someone on the other team rats you out. Which is exactly what happened in 1983 to the Kansas City Royals in a game against the New York Yankees. Royals batter, George Brett, had just hit a home run, which put the Royals in the lead. It had been suspected for a while that Brett had been tarring his bat beyond the legal limit, and this home run was the last straw for Yankees manager, Billy Martin. He brought the suspected illegal bat to the attention of the umpires, and after measuring the bat’s pine tar stain they found it to be well beyond 18 inches. The home run was recalled, and the Yankees went on to win the game.

It doesn’t end there though. After a repeal, it was decided that the dismissal of the home run was the wrong call. If an illegal bat is in play, it should be removed. That’s all. The home run still stands. The Royals and Yankees were ordered to replay the game, starting at the point where Brett had hit his home run. This time the Royals won.

This saga is well known in baseball. There is even a book all about it, as well as a country song and t-shirts. But that’s only part of baseball’s pine tar controversy. While batters are allowed to use it on their bats, pitchers are not allowed to use it to better grip the ball while pitching (however, they can use rosin, which curiously enough, is also made from pine trees). Of course, that doesn’t stop them from trying to get away with it. Sometimes they get caught, like Michael Pineda infamously did in 2014. There are arguments for allowing its use – and perhaps in the future the rules will change – but for now pine tar use by pitchers remains prohibited.

Further Reading – Medicinal Uses for Pine Tar:

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Inside of a Seed: Gymnosperms

“Every tree has to stay where it put down roots as a seedling. However, it can reproduce, and in that brief moment when tree embryos are still packed into seeds, they are free. The moment they fall from the tree, the journey can begin.” — The Hidden Life of Trees by Peter Wohlleben

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Seed plants – also known as spermatophytes – make up the largest group of plants on earth. Seed plants consist of five divisions, and among them the angiosperm division (a.k.a. flowering plants) dominates in its number of species. The four remaining divisions are referred to collectively as gymnosperms. This incudes the cycads (Cycadophyta), Ginkgo biloba (the only living species in the division Ginkgophyta), gnetophytes (Gnetophyta), and the conifers (Coniferophyta). Conifers are by far the largest and most widespread gymnosperm division.

Angiosperms and gymnosperms have different evolutionary histories, resulting in their distinct genetic and morphological differences. That being said, an overly-simplistic way of differentiating the two groups is to say that, while both groups produce seeds, angiosperms produce flowers and fruits while gymnosperms produce pollen cones and seed cones. There are always exceptions (Ginkgo biloba, for example, doesn’t produce cones), but for the most part, this is the case.

Pollen cones (top) and seed cones (bottom) of mugo pine (Pinus mugo) via wikimedia commons

Sexual reproduction in gymnosperms follows a familiar pattern. Pollen, which contains the male sex cells, is produced in pollen cones, which are essentially miniature branches with modified leaves called scales that house the male reproductive organs. Mature pollen is shed and carried away by the wind. Lucky pollen grains make their way to the female cones, which are also modified branchlets, but are a bit more complex. Scales sit atop bracts, and on top of the scales are ovules – the female reproductive structures. During fertilization, the bracts open to collect pollen and then close as the seed develops.

When pollen lands on an ovule it forms pollen tubes that help direct the male sex cells to the egg cells inside. The process is similar to pollen tubes extending down the style of a flower. In flowering plants, additional pollen cells combine with cells in the ovule to produce endosperm, a storage tissue that feeds the growing embryo. This doesn’t happen in gymnosperms. Instead, haploid cells within the ovule develop into storage tissue and go on to serve the same role.

The ovule eventually matures into a seed, and the cone opens to release it. The seed sits atop the scale rather than enclosed within a fruit, as it would be in an angiosperm. For this reason gymnosperms are said to have naked seeds. The development of seeds can also be much slower in gymnosperms compared to angiosperms. In some species, seeds don’t reach maturity for as long as two years.

Seed cones and winged seeds of mugo pine (Pinus mugo) via wikimedia commons

Seeds in the genus Pinus are excellent representations of typical gymnosperm seeds. Their basic components are essentially identical to the seeds of angiosperms. The seed coat is also referred to as an integument. It was once the outer covering of the ovule and has developed into the seed covering. A micropyle is sometimes visible on the seed and is the location where the pollen cells entered the ovule. The storage tissue, as mentioned above, is composed of female haploid cells that matured into storage tissue in the ovule. Like angiosperms, the embryo is composed of the radicle (embryonic root), the hypocotyl (embryonic shoot), and cotyledons (embryonic leaves).

Angiosperms can be divided into monocotyledons and dicotyledons according to the number of cotyledons their embryos have (monocots have one, dicots have two). Gymnosperms are considered multi-cotyledonous because, depending on the species, they can have a few to many cotyledons.

Seedling of Swiss pine (Pinus cembra) showing multiple cotyledons via wikimedia commons

For the sake of this introduction to gymnosperm seeds, I have offered a simple overview of the production of seeds in the conifer division. Sexual reproduction and seed formation in the other three gymnosperm divisions is a similar story but varies according to species. Even within the conifers there are differences. For example, the “seed cones” of several gymnosperm species can actually be quite fruit-like, which serves to attract animals to aid in seed dispersal. Also, the pollen of gymnosperms is often thought of as being wind dispersed (and occasionally water dispersed in the case of Ginkgo biloba and some cycads); however, researchers are continuing to discover the pivotal role that insects play in the transfer of pollen for many cycad species, just as they do for so many species of angiosperms.

All of this to say that Botany 101 is simply a window into what is undoubtedly an incredibly diverse and endlessly fascinating group of organisms, and that, as with all branches of science, there is still so much to discover.