Sunday, July 6, 2014

Plant Story -- Colorful Columbines, Aquilegia

Rocky Mountain columbines,  Aquilegia coerulea
Rocky Mountain columbines,
Aquilegia coerulea
Everybody knows columbine, right?

Columbines, Aquilegia species, are distinctive plants related to anemones and buttercups (in the buttercup family, Ranunculaceae). 

Actually, where you live makes a big difference to what you think a columbine looks like. In eastern North America, there is only one native columbine, Aquilegia canadensis. It has red sepals and spurs on the outside with yellow petals, stigmas and stamens inside. Click on the LINK !

The situation in Europe is similar. There is one common columbine, Aquilegia vulgaris. It has blue to purple sepals with white petals, stigma and stamens. Click on the LINK ! There are almost 20 rare columbine species in the mountains of Europe, but A. vulgaris is far the most widespread. In Latin, “vulgaris” means common, so the common European columbine is aptly named.

If you live in either of those areas, you are likely to have a particular image of columbine in your mind. 

a western columbine with the colors of A. canadensis

an American columbine with the colors of A. vulgaris
In North America, as soon as you reach the Rocky Mountains going west there stops being just one columbine. The Flora of North America gives 21 species in North America, so there are 20 species of columbine in the western North America! They are yellow, blue, white, red, pink…a rainbow of colors (Go to Google link and scroll down). 

Another 20 or more species are spread across Asia, some with large ranges, many with very small ranges. Columbines are a Northern Hemisphere group of cooler climates and higher elevations.



The blue to purple Rocky Mountain Columbine Aquilegia coerulea, is the state flower of Colorado (below and  LINK ) (You will see the scientific name as A. caerulea but the three most authoritative sources I could find spell it A. coerulea.) 

Rocky Mountain columbine, Aquilegia coerulea
Rocky Mountain columbine, Aquilegia coerulea
Of course, cultivated columbines come in many colors. On top of wild species with distinct colors, the columbine species readily hybridize. The colors of the hybrids add even more available colors. 

Columbines cross between species when planted together in gardens, but they also do it in the wild, in the places where one species encounters another. So when you are hiking in western North America, you can encounter columbines that don’t fit anything in your pocket field guide, because you are looking at a hybrid population.

This color variation has attracted North American botanists for easily 100 years. Numerous research projects have looked at why columbines hybridize and what happens to the hybrids. The general answer is that the flowers of each species are adapted to attract particular pollinators, aided by the habitat requirements of both columbine and pollinators. 

I'll talk about North America, since I don’t know as much about Eurasian columbines. 

The distinctive spurs hold nectar (sugar water). Hummingbirds, hawk moths and bumblebees are the most common pollinators of columbines in North America. Hummingbirds are strongly attracted to red. Hawk moths are often nocturnal when light colors are more visible. Bumblebees generally prefer blue, purple and yellow columbines. 

The different pollinators also prefer different flower-shapes. Hummingbird-pollinated columbines tend to be nodding with narrow flowers, in comparison to hawk moth and bumblebee pollinated columbines with broader flowers which more often face upward. (see pictures in link. Also notice the relationship of the pollinators to the flowers they are visiting: hummingbirds, hawk moths and bumblebees.)

Thirdly, hummingbirds' tongues can reach into the columbine's spurs, but the spurs have to be rather broad and not too long. Some species of hawkmoth have very long tongues and can reach into deep, narrow, curved spurs for nectar. Bumblebees like nectar but the spur has to be short and broad. Spurless columbines--and there are varieties and species with spurs so short they are hard to recognize as columbine flowers--are generally pollinated by bees. (Compare the flowers: link )

Hybrids are created when a pollinator carries pollen from the flower of one species to another species. Hummingbirds, hawk moths and bumblebees will all ocassionally check out flowers that are not their preferred color and shape, and those visits can cause hybridization between species. The hybrid is usually less attractive to the pollinators of both its parent species  

Habitat matters too. Different columbine species usually have different habitats. For example, some grow in deep shade, others on shifting open rocky slopes. The hybrid doesn't fit any real environment well and while it may survive, because it is growing poorly, it'll flower less and mature fewer seeds.

Consequently, despite the ease of hybridization of columbines, the preferences of different pollinators for different flower characteristics and their environmental requirements keep columbine species distinct and separate.

columbineTake some time to watch hummingbirds or hawk moths or bumblebees visiting columbines. Great entertainment! 

YouTube: hummingbird in California (I can't find video for the others, let me know if you know a site.)

Columbines come in many different colors and cross easily between species. Explaining the origin of all the variation and why they stay different in nature continues to keep biologists busy. Flor and coauthors, publishing a large and complex paper in 2012, don't imply they've answered all the questions but rather call further study of columbines an "exciting opportunity."  If you aren't in need of a research project right now, just enjoy the diversity of columbines.

Comments and corrections welcome.

References (and there are many other studies, especially of North American columbines)
Bastida, J.M., J. M. Alcรกntara, P.J. Rey, P. Vargas, C. M. Herrera. 2010. Extended phylogeny of Aquilegia: the biogeographical and ecological patterns of two simultaneus but contrasting radiations. Plant Systematics and Evolution. 284:171-185.
Brunet, J., Z. Larson-Rabin and C. M. Stewart. 2012. The distribution of genetic diversity within and among populations of the Rocky Mountain columbine: the impact of gene flow, pollinators, and mating system. International Journal of Plant Sciences 173(5): 484-494.
Chase, V. C. and P. H. Raven. 1975. Evolutionary and ecological relationships between Aquilegia formosa and A. pubescens (Ranunculaceae), two perennial plants. Evolution. 29 (3): 474-486.
Flor, S., M. Li, B. Oxelman, R. Viola, S. A. Hodges, L. Ometto and C. Varotto. 2012. Spatiotemporal reconstruction of the Aquilegia rapid radiation through next-generation sequencing of rapidly evolving cpDNA regions. New Phytologist. 298: 579-592.
Grant, V. 1952. Isolation and hybridization between Aquilegia formosa and A. pubescens. El Aliso. 2 (4): 341-360.
Grant, V. and E. J. Temeles. 1992. Foraging ability of rufous hummingbirds on hummingbird flowers and hawkmoth flowers. Proceedings of the National Academy of Sciences, U.S.A. 89: 9400-9404. 
Wittmore, A.T. 21. Aquilegia Linnaeus, Sp. Pl. 1: 533. 1753; Gen. Pl. ed. 5, 237, 1754. In Flora of North America

Kathy Keeler
Buy the book! Curious Stories of Familiar Garden Plants now available on Amazon link

No comments:

Post a Comment