Ragweed flower anatomy and updates from the field!

Today we got rained out from our regular day of field work, so I thought I would post an update!

CBS undergraduates Eric Holton and Liz Sampson collecting data at the River Terrace field site

CBS undergraduates Eric Holton and Liz Sampson collecting flowering data at the River Terrace field site (rural location)

All the ragweed plants seem to have finally passed peak male and female flowering – data collection was pretty crazy for awhile. They are producing a huge amount of pollen, which is not surprising given that it’s a wind-pollinated plant and a major source of hay fever! Luckily, neither Eric nor I are allergic (yet).

A. artemisiifolia involucres. In the lower right is a single male flower, with two marks along a ruler indicating a length of 1 mm. Image taken from www.backyardnature.net

A. artemisiifolia involucres or “hats” as I call them. In the lower right is a single male flower, with two marks along a ruler indicating a length of 1 mm. Image taken from http://www.backyardnature.net

Common ragweed is a member of the Asteraceae, which is a large family of flowering plants that includes sunflowers and daisies (among many others!). Like other Asteraceae, common ragweed has composite flowers. The male flowers of common ragweed are clustered into little green upside-down bowl-like structures known as involucres, each of which is a single inflorescence. Multiple inflorescences are found along elongated spikes or stalks, and these stalks are found all over the plant! This means a single plant can have thousand of male flowers, each of which is releasing pollen into the air. Hello allergies!

A. artemisiifolia female flowers at the junction of a leaf and the main stem. Image by Graham Calow, taken from www.naturespot.org.uk

A. artemisiifolia female flowers at the junction of a leaf and the main stem. Image by Graham Calow, taken from www.naturespot.org.uk

The female flowers are a little bit harder to spot – they are generally located on stalks below the male inflorescences or at the junction of a leaf and the stem of the plant. Initially all you can see are tiny protruding stigmas (see picture to the left!), which then develop into a single seed.

In my experiment this summer, there are also some really neat all female plants that don’t have a single male flower on them! They are already starting to develop mature fruit as well. I’ll try to include a picture of one of these plants in a future blog post.

Sad, wilted ragweed plants at Scooterville on August 4th, 2015.

Sad, wilted ragweed plants at Scooterville on August 4th, 2015.

The past two weeks were pretty hot in Minneapolis – there were a few 35 C days and it didn’t rain for over a week. I was a bit of a scared that a significant number of plants at the Scooterville site (urban location) were going to die, but I resisted the temptation to water them. I am looking for differences in adaptation between populations after all!

Nevertheless, I am pretty happy that it rained today.

Until next time, fellow ragweed enthusiasts!

Adaptation to urban and rural environments – Germination + Transplanting!

It’s a little late, but finally a post about the experiment I’m doing this summer!

In Fall 2014, I collected seeds from multiple common ragweed (Ambrosia artemisiifolia) populations within urban Minneapolis and in the surrounding rural area. This summer, I am conducting an urban-rural reciprocal transplant experiment using those seeds to determine whether ragweed populations have adapted in response to the selection pressures present in urban and rural environments.

I have four field sites – two located in urban Minneapolis (called St.Paul and Scooterville), and two located in rural locations outside of the Twin Cities (called River Terrace and Rosemount). The Scooterville site is located on the University of Minnesota East Bank Campus and is part of the UMN Living Labs program.

Tilling Scooterville

Eric Holton (UMN undergraduate in EEB), tilling the Scooterville field site

In mid-May, I germinated the seeds in the greenhouse at the UMN and I prepared the sites for planting. This included lots of tilling, which is basically like using a giant lawnmower, but scarier.  In early June, I transplanted the ragweed seedlings out into the four field sites (with the help of others, of course). Overall, the transplanting was a success and most of the plants survived! Hurray!

I’ll be collecting data on these plants over the course of the summer, and I’ll try to post an update now and then with some pictures too! Stay tuned for more on everyone’s favourite plant, ragweed.

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Ragweed germinants successfully transplanted

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The Rosemount field site after transplanting