On the Ecology of Krameria


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.


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. 


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. 


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.  


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]

On Parasites and Diversity


We all too readily demonize parasites. It is kind of understandable though. The thought of something living in or on you at your expense is enough to make our skin crawl. There are a lot of evolutionary pressures that make us look unfavorably about organisms with such lifestyles. However, to completely write parasites off as a bane to life as we know it may be a huge mistake on our part. More and more we are realizing that parasites play an important role in ecosystem functioning and may even serve as indicators of environmental health. 

Plants are no stranger to such parasitic dynamics. Many species have forgone some if not all photosynthetic ability in exchange for a parasitic lifestyle. There is no question that plant parasites can and do have net negative effects on their hosts, however, its never that simple. Research is showing that parasitic plants can have profound effects on the structure and productivity of surrounding plant communities. 

For starters, parasitic plants can increase the competitive ability of non-host species. By knocking back the performance of their host, other plant species can pick up the slack so-to-speak. This can often lead to an increase in overall plant diversity in a given habitat. A common thread throughout studies that have looked at parasitic plants is that proportion of grasses declined when parasitic plants were present. This made room for less competitive forbs to increase in number. In effect, parasitic plants can level the playing field for other, less competitive plant species. 

By altering ecosystem structure, parasitic plants can also alter the way nutrients flow through the system. This can have some seriously profound ramifications. For instance, the presence of the hemiparasitic Rhinanthus minor in grasslands has been shown to  increasing rates of nitrogen cycling. Though the ramifications of this are dynamic, it is nonetheless proof that parasites should not simply be maligned and that, despite our perspective, nature is far more complex than we realize. 

Photo Credit: Sannse (Wikimedia Commons)

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Meet Euphrasia nemorosa, the eyebright. This lovely little plant is native to the northern regions of North America. A quick glance at the flowers of this species may seem to suggest a member of the mint family but this would be wrong. Once placed in Scrophulariaceae, it is now thought to reside in Orobanchaceae. Like other members of this group, E. nemorosa is a hemiparasite. It uses specialized roots to tap into the roots of plants growing around it. In the wild, research has shown that E. nemorosa seems to prefer to parasitize grasses but laboratory experiments have shown that it will parasitize a variety of plants if given the chance. It can even grow without parasitizing other plants but those that did grew small and weak. 

Parasitic plants are an interesting bunch. They push the limits of what is traditionally accepted in the realm of plant physiology. Non-parasitic plants usually have to balance between CO2 uptake and water loss. They do this by controlling their stomata, which are tiny openings on the leaf. Because they are attached to a host, parasitic plants do not have to worry about minimizing water loss and instead want to maximize water loss to gain as much carbon from their host plant as possible. 

Another interesting aspect of Euphrasia ecology is their preference for disturbance. Euphrasia are plants of disturbed meadows, fields, and man-made habitats. There is a lot of work being done to examine which kinds of species thrive in and around humans. Research has shown that by selecting for native species like Euphrasia, the species composition on these types of disturbed habitats can take on a more biodiverse character instead of the usual non-native monoculture.

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