LEAVES: Large, coarsely toothed leaves with short, stiff, sometimes
sticky pubescence. The pungent aroma of the crushed leaves smells rather like
the related herb, tarragon. The leaves remain on the plant well into drought
periods but are readily frost deciduous.
Plants are often found that have numerous pale green warts on the leaf surface. These are caused by nearly microscopic gall mites (Eriophyidae). The mites feed on the plant tissue from the inside of the hollow blisters that are formed by the plant in response to secretions and irritations of the mites. Breaking open the galls will reveal the mites visible with a 20x magnifier.
The Brown Ambrosia Aphid (Macrosiphum ambrosias) finds this a suitable host as does a hispine leaf beetle marked with contrasting red and black and having a rather flattened shape. In some places the California Patch Butterfly, Chlosyne lacinia crocale, is associated with this plant. Thus with many herbivorous insects this important desert wash plant provides for insectivorous birds and reptiles. The thumb links above lead to more information about some of the arthropods associated with Canyon Ragweed.
Asteraceae -- Sunflower Family
Camp Creek, New River Mts., Maricopa Co., Arizona. 14 May 2017.
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