Thursday, August 30, 2012

Giant Ragweed

Weather has been a dominant force in the cycle of life at Blue Jay Barrens this year.  The range of conditions from flood to drought has disrupted the ordered flow of most seasonal events.  Drought continues to be the single most influential event of the year.  A recurring theme across the landscape is the reduced size of most plants due to lack of moisture.  Giant Ragweed is no exception, with the plants being about half their usual height.

The water starved plants try to rebound overnight, but there’s too little available moisture in the soil to do the plants much good.  Wilted leaves droop pathetically during the day.  Perhaps the hurricane remnants will pass through and help alleviate our water deficit.

Despite the dry conditions, the plants are blooming profusely.  The green and yellow flowers surrounding a tall spike at the top of the plant are hardly noticeable. 

Giant Ragweed produces separate male and female flowers.  Those flowers crowding the spike are all male and release a massive dose of airborne pollen.  Hay fever sufferers would definitely not be pushing in to get a close-up of these flowers.

Giant Ragweed is a native annual, so the plant must produce seed to ensure a future generation.  Female flowers are found concealed in leafy bracts growing from the leaf axils at the base of the flower stalk.  Most people don’t even notice these well hidden flowers. 

Typical Giant Ragweed leaves are three lobed like the one shown to the left above.  Many of the Blue Jay Barrens population are unlobed.

On of the most interesting features of the Giant Ragweed is the interaction between the Allegheny Mound Ants, Formica exsectoides and a Treehopper, Publilia concava.  Clusters of these insects are found on almost every plant.

The Treehoppers feed on ragweed sap and as a byproduct of the feeding process, produce honeydew.  The ants feed upon the honeydew.  In their efforts to protect their food supply, the ants provide security for the Treehoppers and the Giant Ragweed plant.

The Treehoppers are fascinating creatures.  The spiky nymphs exhibit a two-tone color pattern that is variable between individuals.  They certainly don’t look like something that is a likely food item.

The adult Treehoppers have a smoother appearance.  They stand out against the bright green of the leaf, but their wide variation in color patterns makes them appear to be a part of the plant.  These adults will overwinter in the leaf litter at the base of the plants and will emerge next spring to mate and begin new colonies.  I hope to always have a nice patch of Giant Ragweed for their use.

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