Last year, I watched a couple of plants growing and growing, waiting to see how tall they would get. One was Giant, or Great Ragweed (Ambrosia trifida). This year, I knew what it was, and having a bit of a hayfever allergy, I pulled it out whenever I noticed it. Ragweed, both giant size and regular size, is plentiful around here, however, and I have to admit, I do admire the amazing altitude it achieves in just one growing season, with some plants easily 10 feet tall.
The leaves make the plant easy to recognise long before its height gives it away. Goldenrod gets blamed for causing allergies, but it is actually ragweed that is the problem. Just as a rule of thumb, plants with showy flowers, like goldenrod, have heavy pollen that they rely on insects to carry around for them. Plants with inconspicuous flowers, like ragweed, use the wind to carry their fine pollen grains. Plants that depend on wind-born pollen produce much more pollen to make up for the imprecise nature of this pollination process. More people are affected by ragweed than all the other species of wind-pollinating plants because ragweed is one of the most potent allergens and has the longest season.
The other giant is Wild Lettuce (Lactuca sp.). It is possibly Tall Blue Lettuce (Lactuca biennis), although one guide observes that due to the large amount of variation in this genus, it is often difficult to identify wild lettuce to the species level. It’s more beneign than giant ragweed and has a rather charming fluffy seedhead at the top of that long, long stalk.
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There are two varieties of plants around the edge of the garden and in the fields here that have been growing and growing and growing all summer. I have been waiting all season to see how tall they would get. Both have produced stalks nine feet tall and more. When Birdgirl was here last, I pointed them out to her and she got out the guides and searched out their identity. The first, shown towering above a stand of garden escapees, is Giant, or Great Ragweed (Ambrosia trifida).
There is lots of ragweed around here, and now giant ragweed as well, it seems. Hmm. No wonder my nose is always running. Ragweed is a common cause of hayfever (not goldenrod, which is often blamed). The leaves of the giant variety are quite distinctive, being large and tri-lobed.
Ragweed flowers aren’t much to look at, but they are interesting to read about. There are male and female flowers, with the male flowers positioned on short stalks along the ends of the stems. The female flowers are located below them where leaves meet the main stem. You can see some really great closeup shots of the flowers here.
Here is a sample of the other plant. I uprooted this plant and laid it out on the ground to get an accurate measurement. Nine feet.
It’s Wild Lettuce (Lactuca sp.). It is possibly Tall Blue Lettuce (Lactuca biennis), although one guide observes that due to the large amount of variation in this genus, it is often difficult to identify wild lettuce to the species level.
The genus name, Lactuca, comes from the latin word lac, meaning milk, and refers to the milky sap that the plants release when the stem is broken. The juice of lettuce plants contains narcotic components. Lettuce sap was once used to produce an opium-like substance. However, wild blue lettuce is not one of the more potent species. The leaves are deeply lobed and similar to big dandelion leaves. Below are the flowers, which top the tall stalk.
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