On the Ecology of Krameria

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There is something satisfying about saying "Krameria." Whereas so many scientific names act as tongue twisters, Krameria rolls of the tongue with a satisfying confidence. What's more, the 18 or so species within this genus are fascinating plants whose lifestyles are as exciting as their overall appearance. Today I would like to give you an overview of these unique parasitic plants.

Commonly known as rhatany, these plants belong to the family Krameriaceae. This is a monotypic clade, containing only the genus Krameria. Historically there has been a bit of confusion as to where these plants fit on the tree of life. Throughout the years, Krameria has been placed in families like Fabaceae and Polygalaceae, however, more recent genetic work suggests it to be unique enough to warrant a family status of its own. 

Regardless of its taxonomic affiliation, Krameria is a wonderfully specialized genus of plants with plenty of offer the biologically curious among us. All 18 species are shrubby, though at least a couple species can sometimes barely qualify as such. They are a New World taxon with species growing native as far south as Paraguay and Chile and as far north as Kansas and Colorado. They generally inhabit dry habitats.

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As I briefly mentioned above, most if not all of the 18 species are parasitic in nature. They are what we call "hemiparasites" in that despite stealing from their hosts, they are nonetheless fully capable of photosynthesis. It is interesting to note that no one has yet been able to raise these plants in captivity without a host. It would seem that despite being able to photosynthesize, these plants are rather specialized parasites. 

That is not to say that they have evolved to live off of a specific host. Far from it actually. A wide array of potential hosts, ranging from annuals to perennials, have been identified. What I find most remarkable about their parasitic lifestyle is the undeniable advantage it gives these shrubs in hot, dry environments. Research has found that despite getting a slow start on growing in spring, the various Krameria species are capable of performing photosynthesis during extremely stressful periods and for a much longer duration than the surrounding vegetation. 

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The reason for this has everything to do with their parasitic lifestyle. Instead of producing a long taproot to reach water reserves deep in the soil, these shrubs invest in a dense layer of lateral roots that spread out in the uppermost layers of soil seeking unsuspecting hosts. When these roots find a plant worth parasitizing, they grow around its roots and begin taking up water and nutrients from them. By doing this, Krameria are no longer limited by what water or other resources their roots can find. Instead, they have managed to tap into large reserves that would otherwise be locked away inside the tissues of their neighbors. As such, the Krameria do not have to worry about water stress in the same way that non-parasitic plants do. 

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By far the most stunning feature of the genus Krameria are the flowers. Looking at them it is no wonder why they have been associated with legumes and milkworts. They are beautiful and complex structures with a rather specific pollination syndrome. Krameria flowers produce no nectar to speak of. Instead, they have evolved alongside a group of oil-collecting bees in the genus Centris.

One distinguishing feature of Krameria flowers are a pair of waxy glands situated on each side of the ovary. These glands produce oils that female Centris bees require for reproduction. Though Centris bees are not specialized on Krameria flowers, they nonetheless visit them in high numbers. Females alight on the lip and begin scraping off oils from the glands. As they do this, they inevitably come into contact with the stamens and pistil. The female bees don't feed on these oils. Instead, they combine it with pollen and nectar from other plant species into nutrient-rich food packets that they feed to their developing larvae.  

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Following fertilization, seeds mature inside of spiny capsules. These capsules vary quite a bit in form and are quite useful in species identification. Each spine is usually tipped in backward-facing barbs, making them excellent hitchhikers on the fur and feathers of any animal that comes into contact with them.  

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

Meet the Sweetfern

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I remember the first time I laid my eyes on Comptonia peregrina. I was new to botany at that point in my life so I didn't have a well developed search image for these sorts of things. I was scrambling down a dry ridge with a scattered overstory of gnarly looking chestnut oaks when I saw a streak of green just below me on a sandy outcropping. They were odd looking plants, the likes of which I had never seen before.

I took out my binoculars to get a better look. What were these strange organisms? Were they ferns? No, they seemed to have woody stems. Were they gymnosperms? No, I could make out what appeared to be male catkins. Luckily I never leave home without a field guide or two. Using what little terminology I knew, I was able to narrow my focus to a plant commonly called a "sweetfern."

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This was one of the first instances in which I grasped just how troublesome common names can be. C. peregrina is mostly definitely not a fern. It is actually an angiosperm that hails from the bay family (Myricaceae). Comptonia is a monotypic genus, with C. peregrina being the only species. It is a denizen of dry, nutrient poor habitats. As such, it has some wonderful adaptations to deal with these conditions.

To start with, its a nitrogen fixer. Similar to legumes, it forms nodules on its roots that house specialized nitrogen-fixing bacteria called rhizobia. This partnership takes care of its nitrogen needs, but what about others? One study found that not only do the roots form nodules, they also form dense cluster roots. Oddly, closer observation found that these clusters were not associated with mycorrhizal fungi. What's more, they also found that these structures were most prevalent in highly disturbed soils. It is thought that this is one way that the plant can maximize its uptake of phosphorus under the harshest growing conditions. 

Flowering in this species is not a showy event. C. peregrina can be monoecious or dioecious, producing male and female catkins towards the ends of its shoots. After fertilization, seeds develop inside bristly fruits. Seed banking appears to be an important reproductive strategy for this species. One study found that germinated seeds had lain dormant in the soil for over 70 years until disturbance opened up the canopy above. It is expected that seeds of this species could exhibit dormancy periods of a century or more. 

In total, this is one spectacular species. Not only does it have a unique appearance, it is also extremely hardy and an excellent species to plant in drought-prone soils wherever it is native. I do see it in landscaping from time to time. If you encounter this species in the wild, take the time to observe it in detail. You will be happy you did!

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

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