The Skeleton Flower - Diphylleia grayi

On the cold, wet mountainsides of Asia and the Appalachians, a unique plant grows tucked away in shady grottoes on the forest floor.  Its singular defining feature, however, can only be seen in Spring, when clusters of bone-white petals unfurl, revealing small, pert flowers wreathed in the few rays of dappled sunlight that manage to pierce the canopy above.  But unlike most flowers, the color of the petals isn’t caused by a pigment, but instead is the result of a unique interplay of light and intercellular structure.  The cells that comprise the petals are widely spaced, with several vacuous lacunae in-between.  These empty spaces are filled with air, and when sunlight is refracted between this air and the cytoplasm of the cells, it imbues the petals with a white hue.  However, when it rains, the petals absorb water, which fill the lacunae; now when sunlight is refracted, it’s between two liquids, that of the absorbed rainwater and the cytoplasm, both of which have similar refractive indices.  This means that when light hits the petals, instead of being reflected back, it can pass straight through the liquid-liquid medium unhindered, causing the flowers to become transparent.

Citations

Yong, J., Chen, F. Yang, Q., Du, G., Shan, C., Bian, H., Farooq, U., & Hou, X. (2015). 

Bioinspired transparent underwater superoleophobic and anti-oil surfaces.  Royal Society of Chemistry 3: 9379-9384.

Original picture retrieved from: http://www.lostateminor.com/2014/11/18/flower-turns-amazingly-transparent-touched-raindrops/

The Werewolf Plant - Ephedra foeminea

It’s a warm, moonlit night in the Balkans.  The landscape is crisp and dry, the rocks underneath sinuous and jumbled, the product of the ancient Himalayan Orogen and millions of subsequent years of erosion and tectonic activity (Milev and Vissileva, 2007).  The Mediterranean breeze permeates the air, and the sky is a cobalt blue, framing the opalescent corona of the moon.  But the moonlight is strangely refracted from a million crystal spheres hidden among the rocks, each visited in turn by moths, expertly navigating the night sky using the azimuth of the moon.  This was the scene recently faced by a team of researchers studying the pollination mechanisms of the genus Ephedra, a type of Gymnosperm common in arid environments.  Entirely by accident, the team had discovered something they weren’t expecting to find: that Ephedra foeminea has a few werewolf-like tendencies when it comes to pollination.

            Ephedra is in the order Gnetales, which for a long time has baffled scientists.  This is a group of plants that looks nothing like the conifers we generally associate with Gymnosperms, and contains such enigmatic species as Welwitschia mirabilis, endemic to the Namib desert and otherwise known as the ugliest plant in the world.  Because of their apomorphous morphological traits, scientists initially thought the Gnetales were sister to flowering plants.  Recent molecular work, however, places Gnetales smack dab in the middle of a now polyphyletic conifer clade, which gives rise to some very interesting evolutionary questions (Bowe et al., 1999; Frohlich, 1999).

            Ephedra itself has a rich history of cultural use.  It was used medicinally as far back as 2700 B.C. when the Chinese used it to treat ailments restricting the bronchial tubes, such as asthma and bronchitis (Guff and Clark, 1928).  Recently, Ephedra has also commonly been used in dietary and energy supplements, but has also been shown to cause strokes and heart problems, prompting the FDA to ban drugs containing Ephedra in 2004 (Guharoy & Noviasky, 2003). 

            But Gymnosperms, including Ephedra, also have a unique type of pollination.  The female egg is located in a structure called the micropyle, comfortably situated within the cone.  When the egg is ready to be fertilized, the micropyle produces a sticky, resinous secretion that forms a globule, which is exposed to the air right about the time when the male strobili are releasing their pollen.  As you probably know from seeing the dense coat of pollen your car receives every spring, Gymnosperm pollen are often dispersed by wind.  Any pollen grain that happens to come into contact with the resinous globule, however, gets stuck, and after a while, the liquid begins to evaporate, causing the globule to contract, gradually pulling the pollen into the micropyle where the sperm is then released to fertilize the egg.

            But in Ephedra foeminea, insects are attracted to the globules, using them as a food source.  This species has therefore evolved to become dependent on insects as pollinators rather than wind.  But the globules are translucent, and, unlike many Angiosperm flowers, don’t produce any distinct odor, so how do insects notice them in the first place?  This brings us back to our team of researchers.  After a few years of collecting data, they had begun to notice that E. foeminea produced pollination droplets at night and about roughly the same time every year, during the summer months of June and July.  But in the summer of 2013, when they went to look for the droplets in Greece, they found nothing.  The weather conditions were the same as the other years in which they had collected, and the team was at a loss as to how to explain the absence.  After a week of searching in vain, they decided to take the night off and grab dinner instead of going into the field.  After comparing notes and pictures from previous collection years, they noticed that their old photographs were much brighter, owing to the presence of a full moon.  They jokingly entertained they idea that there might be a correlation between the moon and pollination droplet production, but as they went through their old data, a pattern began to emerge.  They had to wait another year before there would be a full moon in July, but when they went back to sample that month, sure enough, the droplets were there, the moonlight glinting off their surface creating tiny little beacons for moths to find their way to them (Coghlan, 2015; Rydin & Bolinder, 2015). 

            E. foeminea is currently the only known plant species that synchronizes its release of pollen with the full moon, but how it does so still remains somewhat of a mystery.  Plants can sense gravity, and actually use it to orient themselves right side up when they begin to grow from their embryonic state (Baluška, 2006).  They can also sense moonlight, including its different phases (Garner, 1937; Bünning, 1969).  Interestingly, E. foeminea also appears to grow further away from cities and towns than its close relatives, which are wind pollinated, indicating there may be a link between the human interference of artificial and ambient light and the success of this species.  But out in secluded areas of the Balkans, under the light of the full moon, E. foeminea can still be seen producing crystalline orbs, which glint and weave in a complex interplay of light, resin, and pollen-laden moths.

Citations

Bowe, L. M., Coat, G., & dePamphilis, C. W. (1999). Phylogeny of seed plants based on

all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales’ closest relatives are conifers. Proc. Natl. Acad. Sci. 97(8): 4029-4097.

Coghlan, A. (2015, April 11). Werewolf plant waits for the light of the full moon. New

            Scientist.

Frohlich, M. W. (1999). MADS about Gnetales. Proc. Natl. Acad. Sci. 96: 8811-8813.

Groff, G. W. & Clark, G. W. (1928). The botany of Ephedra in relation to the yield of

            physiologically active substances. Univ. Calif. Publ. Bot. 14: 247-282.

Guharoy, R. & Noviasky, J. A. (2003). Time to ban ephedra – Now. American Journal

            of Health-System Pharmacy 60: 1580-1582.

Milev, G. & Vassileva, K. (2007). Geodynamics of the Balkan Peninsula and Bulgaria.

International Symposium on Strong Vrancea Earthquakes and Risk Mitigation, pp. 55-70.        

Rydin, C. & Bolinder, K. (2015). Moonlight pollination in the gymnosperm Ephedra

            (Gnetales). Biology Letters 11: 1-4.