The Hidden Anatomy of Grass Flowers

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Grass flowers have their own unique beauty. Examine them with a hand lens and a whole new world of angiosperm diversity suddenly opens up. Unlike other flowering plants, their charm lies not in showy sepals or petals, but in an intricacy centered around the utilization of wind for pollination. However, such floral organs are not lacking. Grass flowers do in fact produce a perianth, the function of which has been highly modified.

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To see what I am referring to, you need to do some dissection under a scope. Pull off a flower and peel away the sheaths (the palea and lemma) that cover it. Inside you will see an ovary complete with feathery stigmas as well as the anthers. At the base of the ovary sits a pair of scales called lodicules. These lodicules are thought to be the rudimentary remains of the perianth. They certainly don't resemble sepals or petals but that is because the function of these structures is not to attract pollinators. They assist in pollination in another way.

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When grass flowers are ready for reproduction, the lodicules begin to swell. This swelling serves to push apart the rigid palea and lemma that protected the flowering parts as they developed. Once apart, the anthers and stigma are free to emerge and let wind do the dirty work for them. Lodicules differ quite a bit from species to species in their size, shape, and overall appearance. Much of this is likely tied to the overall structure in grass flowers.

Photo Credits: [1] [2]

Further Reading: [1]

 

Grass Defenses

Cut grass, sword grass, ripgut? All of these names have been applied to grasses. It may seem strange to attach such sharp adjectives to grasses but run through a prairie full of Leersia oryzoides or Spartina pectinata with shorts on and you will quickly learn why. As innocuous as they may look, grasses are well defended.

What looks like the mouth of a shark is actually a blade of grass. As you can see, it is covered in microscopic, razor sharp daggers. The daggers themselves are specialized structures called "phytoliths." Grasses manufacture phytoliths from silica that they absorb from the soil. Not all species produce these daggers. Some distribute phytoliths throughout their leaves, essentially packing themselves with tiny granules of glass. Their presence is an adaptation against herbivory. 

It's not hard to imagine how effective silica daggers can be. Run your finger along the stem or leaves of one of these grasses and you are likely to draw blood. Early settlers coined the term "ripgut grass" because the bellies of horses and other livestock would get seriously lacerated from running through it. Whereas this defense is rather straight forward, the other types of phytoliths are a little more subtle in their effectiveness. 

Silica is tough and chewing on leaves chock full of it can do a real number on your teeth. That is the main reason why the teeth of many grass grazers alive today grow continuously. If their teeth were like ours, the phytoliths within the blades of grass would wear them down to useless nubs. In fact, the evolution of phytoliths in grass is thought to have ushered in a new age of grazing mammals via the extinction of those that could not cope with these microscopic defenses. 

It's not just about teeth either. Insects feeding on blades of grass may be able to get past the phytoliths without an issue but the story changes once it makes it to the gut. Silica particles have been shown to interfere with digestion. Caterpillars feeding on grasses containing high amounts of silica in their leaves had decreased levels of digestion efficiency, which resulted in reduced growth rates. Unlike other plants, grasses can handle certain amounts of grazing because their growth tips are located beneath the soil rather than near the tips. As such, they can afford to gradually weaken the effectiveness of their predators. 

I have gained a new appreciation for grasses since moving to the prairies. This diverse order of plants has shaped the world we see today in a very big way. Because they don't have showy flowers, grasses are often overlooked as nothing more than turf. In reality, they are fascinating organisms supremely adapted to what the environment throws at them. One could only wish to be as hardy as a grass. 

Photo Credits: [1] [2]

Further Reading: [1] [2] 

Hyperabundant Deer Populations Are Reducing Forest Diversity

Synthesizing the effects of white-tailed deer on the landscape have, until now, been difficult. Although strong sentiments are there, there really hasn't been a collective review that indicates if overabundant white-tailed deer populations are having a net impact on the ecosystem. A recent meta-analysis published in the Annals of Botany: Plant Science Research aimed to change that. What they have found is that the overabundance of deer is having strong negative impacts on forest understory plant communities in North America.

White-tailed deer have become a pervasive issue on this continent. With an estimated population of well over 30 million individuals, deer have been managed so well that they have reached proportions never seen on this continent in the past. The effects of this hyper abundance are felt all across the landscape. As anyone who gardens will tell you, deer are voracious eaters.

Tackling this issue isn't easy. Raising questions about proper management in the face of an ecological disaster that we have created can really put a divide in the room. Even some of you may be experiencing an uptick in your blood pressure simply by reading this. Feelings aside, the fact of the matter is overabundant deer are causing a decline in forest diversity. This is especially true for woody plant species. Deer browsing at such high levels can reduce woody plant diversity by upwards of 60%. Especially hard hit are seedlings and saplings. In many areas, forests are growing older without any young trees to replace them.

What's more, their selectivity when it comes to what's on the menu means that forests are becoming more homogenous. Grasses, sedges, and ferns are increasingly replacing herbaceous cover gobbled up by deer. Also, deer appear to prefer native plants over invasives, leaving behind a sea of plants that local wildlife can't readily utilize. It's not just plants that are affected either. Excessive deer browse is creating trophic cascades that propagate throughout the food web.

For instance, birds and plants are intricately linked. Flowers attract insects and eventually produce seeds. These in turn provide food for birds. Shrubs provide food as well as shelter and nesting space, a necessary requisite for healthy bird populations. Other studies have shown that in areas that experience the highest deer densities songbird populations are nearly 40% lower than in areas with smaller deer populations. As deer make short work of our native plants, they are hurting far more than just the plants themselves. Every plant that disappears from the landscape is one less plant that can support wildlife.

Sadly, due to the elimination of large predators from the landscape, deer have no natural checks and balances on their populations other than disease and starvation. As we replace natural areas with manicured lawns and gardens, we are only making the problem worse. Deer have adapted quite well to human disturbance, a fact not lost on anyone who has had their garden raided by these ungulates. Whereas the deer problem is only a piece of the puzzle when it comes to environmental issues, it is nonetheless a large one. With management practices aimed more towards trophy deer than healthy population numbers, it is likely this issue will only get worse.

Photo Credit: tuchodi (http://bit.ly/1wFYh2X)

Further Reading:
http://aobpla.oxfordjournals.org/content/7/plv119.full

http://aobpla.oxfordjournals.org/content/6/plu030.full

http://www.sciencedirect.com/science/article/pii/S0006320705001722