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!

6 weeks and growing!

First of all – Happy Canada to all! If I ever get around to it, I’m going to make a page with amusing Canadian items, like the Long John Service Index of Canada.

The ragweed plants are happily growing and are getting huge! Last week I visited all my field sites to do some growth measurements on the plants at 6 weeks. There is a lot of variation in size of plants between the four field sites – the plants at the St.Paul site (urban garden) appear to be the largest, and those at the River Terrace site (rural garden) appear to be the smallest. I don’t know what is driving these size differences, however I have a feeling it might be due to soil differences between the sites. This gives me further motivation to do some sort of follow-up greenhouse experiment with the soil from these field sites to determine whether it is affecting plant growth and fitness.

Ragweed plants at St.Paul field site (6 weeks old!)

Ragweed plants at the St.Paul field site (6 weeks, urban location)

Ragweed plants at the River Terrace field site (6 weeks, rural location)

Ragweed plants at the River Terrace field site (6 weeks, rural location)

The beginning of flower development on a ragweed plant at the Scooterville field site.

The beginning of flower development on a ragweed plant at the Scooterville field site.

The plants have also started to initiate flower development! I was surprised to see this as A. artemisiifolia doesn’t  normally start to flower until late July or early August. I will be tracking and recording the emergence of both the male and female flowers as the season progresses with plastic party swords – I have to keep data collection exciting, right?