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The Origin of the Sepal Crest in Iris

Jinyan Guo

Botany student Jinyan Guo researches a group of plants in a genus with one of the most popular garden flowers in the world: the iris. But while many of us admire the bright colors (the name iris is derived from the Greek word for rainbow, after all), Guo looks at the novel structure of sepal crests in irises, which provide insight into the plant’s unique evolutionary story.

Guo—a doctoral candidate—attributes her interest in plant life to her upbringing in a city in the Shanxi province in China.

“I think it is partly my nature to love plants. But also, there weren’t a lot of gardens where I grew up. Not being able to see them so often got me even more interested in plants—especially flowers,” she said.

That is why she devoted her undergraduate and graduate work to them. She completed her master’s thesis at the Beijing Botanic Garden, Institute of Botany, Chinese Academy of Science, where she focused on iris horticulture, seeking new methods for breeding and increasing production. While writing her thesis, she came across a paper by CGU Research Professor Carol A. Wilson, who has devoted much of her career to studying the genus Iris. Guo wrote to Wilson about their mutual research interests and ended up applying to CGU’s Botany program.

When she began her doctoral work at CGU, Guo shifted from horticulture to phylogenetic (the study of evolutionary relationships among organisms) and morphological (the study of the form and structure of organisms and their specific structural features) research. In the genus Iris, Guo looks at the unique structure of the sepal crest within the bud of crested irises. Like hood ornaments on vintage autos, crests project vertically from the otherwise flat surfaces of the sepals of Iris flowers. The morphologies of sepal crests are particularly diverse in the Chinese species, which made them especially intriguing for her.

To understand this research, it is important to note that while there are around 270 species in the genus Iris, the iris flowers you see at your local florist likely come from Iris germanica, a single, bearded species for which there are more than 10,000 cultivars. Of the less frequently cultivated Iris species, 58 have sepal crests: ridges or cockscombs of often elaborately colored and fringed tissue that are perpendicular to the sepal. In crested Iris species, the growth of the sepal crest gives rise to a three-dimensional sepal. For Guo, these components make those 58 species of Iris intriguing and worthy of detailed study.

“Within this small group there is a unique structure that is so diverse. That’s what is so interesting,” she said. “If there is a weird structure that appears once it is not surprising. But if an unusual structure has evolved multiple times, that’s very interesting.”

Guo frequently travels back to her native China, and has made one trip to Missouri to collect samples of crested irises. At the Rancho Santa Ana Botanic Garden research facilities, she dissects the flower’s sepals and uses a critical point dryer to process her plant materials. She then coats these samples in gold om a sputter coater to prepare them for viewing under a scanning electron microscope. Guo is able to take detailed images of different species and at different developmental stages for each species.

“She is looking at something that’s never been looked at before,” said Wilson. “It’s unique. With her ideas, she’s been able to capture new ways of looking at crests that makes them more exciting. She’s been a very successful graduate student.”

With these images she can then compare the morphology of sepal crests in Iris. She looks to discover pattern development among the different lineages of crested irises that share a close phylogenic background. Currently, her research is focused on identifying how these species of Iris have evolved. Why they have evolved is an intriguing question as well, and one she hopes to tackle after receiving her PhD.

“The ultimate question I want to answer is why some irises have evolved a certain way while others haven’t, and if there are any selective advantages to how these structures evolved,” she said. “I’m not covering that in my PhD research. But that is the next step.”

In fact, Guo sees research on the genus Iris as an endeavor that she can devote her entire career toward. For someone who grew up in a city with little plant life, decades spent studying flowers should make up for lost time.

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