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Cleaning Echinacea Heads

For the past three weeks, I’ve been hard at work collecting the achenes from Echinacea heads that were collected last summer from Staffanson Prairie Preserve. A little bit of Echinacea anatomy to give you a better idea of what I’m talking about: each head typically consists of 100 to several hundred small flowers or florets. After the head has matured and the florets have finished blooming, every flower produces one fruit, known as an achene, regardless of whether or not it was fertilized. Back at the lab, we clean all the achenes off the heads in order to count them and determine whether or not they contain a viable seed.

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An intact head

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Achenes

In addition to cleaning the heads, I have also been separating the achenes by where on the head they were located. The florets bloom row-by-row starting from the base of the head and working their way up, so we know that the florets at the bottom bloomed first and the ones at the top bloomed last. Looking at reproductive success via seed set on the top, middle, or bottom of each head will thus give an indication of how the mating scene and pollen availability changed over the course of the mating season.

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Hard at work cleaning a head

Cleaning the heads is the first step in determining seed set, the primary measure of reproductive success I’ll be using for this project. Seed set is defined as the proportion of seeds that were successfully fertilized, and this number can range from zero to nearly 100%. While there are many reasons that fertilization may have failed, the primary reason is most likely a lack of compatible pollen. Now that all the achenes have been removed from the heads, I can determine what proportion of achenes on each head contains an embryo using x-ray. I’ll go into more depth about the x-raying process in another post.

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