(A) Young yellow-orange pseudoflower. (B) Mature pseudoflower. (C) Longitudinal section of an infected X. surinamensis inflorescence. (D) Healthy yellow flower of X. surinamensis shown for comparison. [SOURCE] — (A) Young yellow-orange pseudoflower. (B) Mature pseudoflower. (C) Longitudinal section of an infected *X. surinamensis* inflorescence. (D) Healthy yellow flower of *X. surinamensis* shown for comparison. [SOURCE]

Imagine there was a fungus that was able to hijack human reproductive structures so that it could reproduce. Though this sounds like the basis of a strange science fiction story, a similar situation to this has just been described from Guyana between two species of yellow-eyed grass (Xyris setigera & X. surinamensis) and a newly described species of fungus called Fusarium xyrophilum.

Fungi that hijack plant reproductive systems are pretty rare in nature, especially when you consider the breadth of interactions between these two branches on the tree of life. What makes this newly described case of floral hijacking so remarkable is the complexity of the whole process. It all begins when an infected Xyris host begins to produce its characteristically lanky inflorescence.

At first glance, nothing would appear abnormal. The floral spike elongates and the inflorescence at the tip gradually matures until the flowers are ready to open. Even when the “flower” begins to emerge from between the tightly packed bracts the process seems pretty par for the course. Gradually a bright yellow, flower-like structure bursts forth, looking very much like how a bright yellow Xyris flower should look. However, a closer inspection of an infected plant would reveal something very different indeed.

Instead of petals, anthers, and a pistil, infected inflorescences produce what is called a pseudoflower complete with petal-like structures. This pseudoflower is not botanical at all. It is made entirely by the Fusarium fungus. Amazingly, these similarities are far from superficial. When researchers analyzed these pseudoflowers, they found that they are extremely close mimics of an actual Xyris flower in more than just looks. For starters, they produce pigments that reflect UV light in much the same way that actual flowers do. They also emit a complex suite of volatile scent compounds that are known to attract pollinating insects. In fact, at least one of those compounds was an exact match to a scent compound produced by the flowers of these two Xyris species.

So, why would a fungus go through all the trouble of mimicking its hosts flowers so accurately? For sex, of course! This species of Fusarium cannot exist without its Xyris hosts. However, Xyris don’t live forever and for the cycle to continue, Fusarium must go on to infect other Xyris individuals. This is where those pseudoflowers come in. Because they so closely match actual Xyris flowers in both appearance and smell, pollinating bees treat them just like flowers. The bees land on and investigate the fungal structure until they figure out there is no reward. No matter, they have already been covered in Fusarium spores.

As the bees visit other Xyris plants in the area, they inevitably deposit spores onto each plant they land on. Essentially, they are being coopted by the fungus in order to find new hosts. By mimicking flowers, the Fusarium is able to hijack plant-pollinator interactions for its own reproduction. It is not entirely certain at this point just how specific this fungus is to these two Xyris species. A search for other potential hosts turned up only a single case of it infecting another Xyris. It is also uncertain as to how much of an impact this fungus has on Xyris reproduction. Though the fungus effectively sterilizes its host, researchers did make a point to mention that Xyris populations may actually benefit from having a few infected plants as the pseudoflowers last much longer than the actual flowers and therefore could serve to attract more pollinators to the area over time. Who knows what further investigations into the ecology of this bizarre system will reveal.

Photo Credit: [1]

Further Reading: [1]

Over the last decade I have become quite familiar with the flora of western New York. I love and adore the species that call my neck of the woods home. For this reason, I get extra excited when I encounter something new. Identifying a plant I have never seen before is one of the best parts about botanizing. Having that species represent a family of plants entirely new to me is truly the icing on the cake.

Bogs are some of my favorite habitat types. Their complexity in structure is well complemented by the myriad species that haunt the soggy terrain. They are made all the more wonderful when you consider their age. Bogs are glacial relicts, having existed unchanged since this region was freed from its icy grip. On a recent bog slog something different caught my eye. What appeared to be an odd clump of grass quickly revealed itself to be something new and different.

Photo by Bob Peterson licensed under CC BY 2.0

Sitting atop some of the blades were leathery clusters of bracts. Poking out from between these bracts were little yellow tufts. A closer inspection revealed that these tufts were three delicate petals of a flower unlike anything I was familiar with. Field guides were consulted and this odd little plant turned out to be a member of the group commonly referred to as yellow-eyed-grass. My first thoughts on this went immediately to the genus Sisyrinchium, those not-so-iris-like members of the iris family. Though they are similar in appearance, the yellow-eyed-grasses are not related to blue-eyed-grasses at all.

Yellow-eyed-grasses not only belong in their own genus - Xyris - they also belong in their own family - Xyridaceae. They are more closely aligned with grasses than they are other flowering plants. There are something like 5 genera nestled into this family but a majority of the representatives belong in the genus Xyris. The plant I had found was Xyris difformis, the bog yellow-eyed-grass. They are plants of wet places, specializing in wetlands, bogs, and shorelines. Their ecology is interesting in that they sort themselves out along wave gradients, with most species preferring enough wave action to provide the proper soil texture and to limit competition from other wetland plant species.

This group is incredibly interesting. They are also quite beautiful. Some species are becoming rare in North America as we continue to turn wetlands into housing developments and strip malls. With a global distribution, many of you are likely to encounter a member of Xyridaceae in your neck of the woods as well. Simply keep you eye open for any strange "grasses" growing in wet areas.

Flower photo: Bob Peterson (http://bit.ly/1IcamFN)