Fennel is a ubiquitous weed around here. I like growing dill in my garden. And I find that, although they are in two different genera (Foeniculum vs. Anethum), they seem to look just alike. So I searched the internet for how to tell them apart. Guess what? Even articles purportedly about how to tell them apart, didn’t actually say how to tell them apart, other than by scent – fennel has an overpowering licorice scent, dill does not.
More worrisome was Wikipedia, saying that they can hybridize, and when they do, the fennel predominates. Worrisome because I don’t want my dill crop to become “fennelized.” Either this is a rare case of intergeneric hybridization, or, like previous purported intergeneric hybrids, they get reclassified as the same genus.
But that raised a question in my mind: how have they remained separate species? They seem to have both been originally native to the Mediterranean region, i.e. sympatric, so given that they did not merge into a single species in ancient times, there must be some barrier to hybridization (albeit not a perfect one).
I wonder if I have found it. The other day, I was observing a large field of weedy fennel, and its flowers were full of honey bees. My dill crop’s flowers draw hover flies and greenbottles. I did not see any flies on the wild fennel, and I have not seen any bees at my dill. So that got me to wondering if perhaps their barrier to hybridization is different pollinators.
But then, it may be that my dill plants are too few to attract honey bees, which tend to work only the most abundant flower in the area when there is one; and that if the dill was as extensive as the fennel, bees would work it. Or, it may be that the density of bees on the fennel deterred flies which would otherwise have come. Still, it is a suggestive, preliminary observation. And an encouraging one, since it suggests that my dill plants are not receiving fennel pollen.
I also saw one pollinator shared by both: the European paper wasp (commonly mistaken for a yellowjacket). So even if the bees vs. flies distinction is ecological reality, the wasp makes it an imperfect distinction.