HannahGrace, that may be a question for allergy specialists.
I kind of think of ragweed as just being wherever I go on some old dirt road . .
. Okay, I know it is everywhere but there sure has been a lot of it, some of the places where I've lived.
Chamomile is something I've grown but decided against continuing with it. Chamomile just didn't grow well enuf in my yard. It might have done well in a more open location. I do like it as a tea
Both of these plants are in the Aster family but so are many, many others. They differ by genus, as well as species. So, just looking at an Aster family list, they don't appear to be closely related.
Ragweed is an Ambrosia. Chamomile is an Anthemis but this family is huge:
[url=https://plants.usda.gov/java/ClassificationServlet?source=profile&symbol=Asteraceae&display=31]Aster Family, USDA[/url]