purpleinopp said:
I've never read a formal description or plant ID key that said a plant was not either annual or perennial (and sometime biennial.) I've never seen a resource that said there was variation in or interpretation of whether or not a plant was annual vs. perennial (or biennial) just that plants can behave as one or the other depending on location/climate. If it's just being used as a matter of personal interpretation, and/or to indicate the behavior of a plant, which I think is what you are both saying, Kent and Janet, I maintain respectful disagreement about these definitions being malleable to personal interpretation, outside the context of behavior.
The definitions are not malleable, but the plants most certainly are.
I'll come back to the Musk Thistle example simply because it's easy, but many, many plants behave the same way. I've seen Musk Thistles growing as annuals, winter annuals, biennials, and perennials in the same field at the same time. Environmental conditions play a role, but they aren't the important factor.
Words like "annual" or "perennial" are just inventions of the human mind, an attempt to make sense of an extremely complex world. Plants care not for the boxes we try to fit them in. All they are trying to do is pass their genes from one generation to the next, by whatever means are available to them. For most plants, the variability of those means is quite surprising and spectacular, including acting like a perennial, biennial, or annual depending on what is to their greatest advantage at the moment.
As for the plant keys, there's always a difficult balancing act between accuracy and usability with keys. The more technically accurate they become, the less usable they are. For example, the key sitting in front of me right now says:
26. Inflorescences of spicate racemes borne singly.......Schizachyrium scoparium (little bluestem)
26. Inflorescences of 2-7 spicate racemes............Andropogon gerardii (big bluestem)
That's true probably more than 95% of the time, but it isn't ALWAYS true (big bluestem occasionally produces inflorescences that are borne singly). Keys are designed to point you in the right direction most of the time, but it is impossible for them to be right all of the time (because plants exhibit a LOT of variability
). That said, if you've never seen a key with something like "Plants perennial or annual", you might want to look for some better quality keys
. I see that sort of language in keys routinely.
