Birds Work a Double Shift For Osmoxylon

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Plants go to great lengths to achieve pollination. Some can be tricky, luring in pollinators with a promise of food where there is none. Others, however, really sweeten the deal with ample food reserves. At least one genus of plants has taken this to the extreme, using the same techniques for pollination as it does for seed dispersal. I present to you the genus Osmoxylon.

Comprised of roughly 60 species spread around parts of southeast Asia and the western Pacific, the genus Osmoxylon hail from a variety of habitats. Some live in the deep shade of the forest understory whereas others prefer more open conditions. They range in size from medium sized shrubs to small trees and, upon flowering, their place within the family Araliaceae becomes more apparent.

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Look closely at the flowers, however, and you might notice a strange pattern. It would appear that as soon as flowers develop, the plant has already produced berries. How could this be? Are there cleistogamous flowers we aren't aware of? Not quite. The truth, in fact, is quite peculiar. Of the various characteristics of the genus, one that repeatedly stands out is the production of pseudo-fruits. As the fertile flowers begin to produce pollen, these fake fruits begin to ripen. There aren't any seed inside. In truth, I don't think they can technically be called fruits at all. So, why are they there?

Although actual observations will be required to say for sure, the running hypothesis is that these pseudo-fruits have evolved in response to the presence of birds. They are pretty fleshy and would make a decent meal. It is thought that as birds land on the umbel to eat these pseudo-fruits, they invariably pick up pollen in the process. The bird the exchanges pollen with every subsequent plant it visits. Thus, pollination is achieved.

The relationship with birds doesn't end here. Like other members of this family, pollination results in the formation of actual fruits full of seeds. Birds are known for their seed dispersal abilities and the Osmoxylon capitalize on that as well. As such, the reproductive input of their avian neighbors is thought to be two-fold. Not only are birds potentially great pollinators, they are also great seed dispersers, taking fruits far and wide and depositing them in nutrient-rich packets wherever they poop.

Photo Credits: [1] [2]

Further Reading: [1]

A Peculiar Case of Bird Pollination

When we think of bird pollination, we often conjure images of a hummingbird sipping nectar from a long, tubular, red flower. Certainly the selection pressures brought about from entering into a pollination syndrome with birds has led to convergence in floral morphology across a wide array of different plant genera. Still, just when we think we have the natural world figured out, something new is discovered that adds more complexity into the mix. Nowhere is this more apparent than the peculiar relationship between an orchid and a bird native to South Africa.

The orchid in question is known scientifically as Disa chrysostachya. It is a bit of a black sheep of the genus. Whereas most Disa orchids produce a few large, showy flowers, this species produces a spike that is densely packed with minute flowers. They range from orange to red and, like most other bird pollinated flowers, produce no scent. 

Take the time to observe them in the field and you may notice that the malachite sunbird is a frequent visitor. The sunbirds perch themselves firmly on the spike and probe the shallow nectar spurs on each flower. At this point you may be thinking that the pollen sacs, or pollinia, of the orchid are affixed to the beak of the bird but, alas, you would be wrong. 

Closer inspection of the flowers reveal that the morphology and positioning of the pollinia are such that they simply cannot attach to the beak of the bird. The same goes for any potential insect visitors. The plant seems to have assured that only something quite specific can pick up the pollen. To see what is really going on, you would have to take a look at the sunbird's feet. 

That's right, feet. When a sunbird feeds at the flowers of D. chrysostachya, its feet position themselves onto the stiffened lower portion of the flower. This is the perfect spot to come into contact with the sticky pollinia. As the bird feeds, they pick up the pollinia on their claws! The next time the bird lands to feed, it will inevitably deposit that pollen. The orchids seemed to have benefited from the fact that once perched, sunbirds don't often reposition themselves on the flower spike. In this way, self pollination is minimized. A close relative, D. satyriopsis, has also appeared to enter into a pollination with sunbirds in a similar way. 

Though it may seem inefficient, research has shown that this pollination mechanism is quite successful for the orchid.The pollinia themselves stick quite strongly so that no amount of scuffing on branches or preening with beaks can dislodge them. Once pollination has been achieved, each flower is capable of producing thousands upon thousands of seeds.

Photo Credit: Johnson and Brown

Further Reading: [1]

Darwin's Slipper


Along the craggy peaks of the Andes from Chile into Argentinia, and down into Patagonia grows a strange alpine plant known scientifically as Calceolaria uniflora.  It goes by the common name of Darwin's Slipper as many attribute its discovery to Charles Darwin, however, this plant was first collected by French naturalist Philibert Commerson in 1767, 42 years before Darwin was even born. Regardless, C. uniflora is a remarkable little plant. It stands as an ornate example of a unique pollination syndrome, one that that is quite apt considering who discovered it. As with any strange flower, once you begin to ponder the significance of its morphology, you inevitably come to the same question; what on Earth pollinates it?


As a whole the genus Calceolaria is bee pollinated. Relying on what are known as "oil bees," most of the flowers in this genus produce hairs that secret oils that the female bees relish. Calceolaria uniflora is different from the rest in that it doesn't bother with oil production. Instead of producing flowers with a tube or a pouch, this species creates an almost alien-looking red and orange bloom with a bright white appendage on its lower lip. What is going on there? The answer to this strange riddle has a clue in where this species grows.

At high altitudes, oil-collecting bees are scarce. It is simply too cold and harsh for many insects to survive at such elevations. Instead, what are present are birds, specifically a species of seedsnipe. These little birds exist on a plant-based diet and spend a lot of their time holding territories and grazing on seeds and fruits of a handful of alpine plants. Researchers noticed that patches of Calceolaria uniflora growing around these birds seemed to have high levels of floral damage, specifically on the lower lip where the white appendage is located. In fact, the white appendage was often completely removed.

As it turns out, the seedsnipes regularly visit patches of these flowers and proceed to peck off and eat the white appendage. As the birds peck off these appendages, the anthers and stigma bash against the birds head. As it does, pollen is dusted onto the bird as well as onto the female parts of the flower. Thus pollination is achieved. But what's in it for the birds? As it turns out, when tested in the lab, researchers found these appendages to be high in sugars. The birds are in it for an easy, sugary meal.

When we think of birds as pollinators, we often think of hummingbirds or honeyeaters. The relationship between Calceolaria uniflora and the seedsnipe is rather outlandish in comparison but it certainly works for both species. The lack of insect pollinators has driven Calceolaria uniflora towards an alternative pollinator and quite a unique one at that!

Photo Credit: Julio Martinich (http://bit.ly/1TMiqk7)

Further Reading:
http://bit.ly/1OJCahs