An Exploration of the Fringe: What’s Blooming in the Smithsonian Gardens Orchid Collection
Winter is one of the most prolific bloom times in the Smithsonian Gardens orchid greenhouses and each year I am astounded by the diversity that is on display. I have a predilection for miniature orchids, for bizarre traits and unique stories and the two orchids featured today will not disappoint.
Bulbophyllum saltatorum var. albociliatum is an exquisite species found widely across Central Africa. Its winter-blooming flowers are no bigger than a thumbnail, and like many Bulbophyllums, the lip has been dramatically modified. In this case, the modification takes the form of a bright pink fringe, which acts as a lure for small flies who end up inadvertently pollinating the flower. This species is also rather unique for a Bulbophyllum because its scent is quite pleasant (at least to my olfaction).
Fringe is not purely used for deceptive purposes. This characteristic, along with colorless flowers and night fragrance is a pollinator syndrome for Hawk Moths. Various species of Brassavola and Habenaria exhibit a unique variation of this morphological adaptation, and offer nectar rewards to their nocturnal visitors. It is not certain what characteristic of this fringed lip appeals to the Hawk Moth, but the convergence of this trait across unrelated orchid genera implies that it is pollinator specific.
In their infinite diversity, orchids always manage to deconstruct the carefully deduced generalizations scientists make about their biology. The Clowesia below, Clowesia Grace Dunn, is a hybrid between Clowesia rosea and Clowesia warzewiczii and as you can see, has an arresting display of fringe on its lip as well.
These flowers are NOT moth pollinated, rather they are visited by crepuscularly active Euglossine bees that collect their fragrances in the form of oils to woo lady bees. Typically, Euglossine bees are generalists, and will collect fragrances from a number of different species. It has been theorized that the fragrances of Clowesia species change throughout the day, with an “optimal fragrance” either before dawn or just after dusk when their pollinators are most active. This may seem like a wild concept, but many biological functions occur in a cyclical fashion, and solely night fragrant orchids are commonly referenced. It makes sense that the same mechanism would be at work in crepuscularly, diurnally and nocturnally fragrant plants.
Daily fragrance fluctuations are not unique to Clowesia, and have been studied previously in Arachnis, Vanda, Spathoglottis and Oncidium (Goh, 1983), among others. The variation in fragrance could be influenced by changes in acidity due to CO2 production during Crassulacean Acid Metabolism (Goh, 1983) and is decidedly affected by photoperiod, an indication that fragrance is regulated by a circadian rhythm (Altenburger & Matile, 1990).
I never considered the importance of physiological constraints playing such a vital role in the evolution of plant-pollinator relationships, but evidence for this “biological clock” of fragrance emission throughout the plant world is incredibly fascinating. Orchid pollination is a beautifully complex fabric of not only interactions (deceptive or otherwise), but the timing of these interactions. As I am often reminded, NOTHING is coincidence, but the intricacies of evolution often seem astoundingly fortuitous.
–Julie Rotramel, Living Collections Specialist
Altenburger, R., & Matile, P.. (1990). Further observations on rhythmic emission of fragrance in flowers. Planta,180(2), 194–197. Retrieved from http://www.jstor.org/stable/23380097
Goh, C. J.. (1983). Rhythms of Acidity and CO2 Production in Orchid Flowers. The New Phytologist, 93(1), 25–32. Retrieved from http://www.jstor.org/stable/2431891