Martin Harvey's picture

Perennial vs. annual

I've been trying out the new Vegetative Key to the British Flora (by John Poland and Eric Clements). In some of the keys I'm asked to choose whether the plant I'm looking at is perennial or annual. How do you tell from looking at a plant which of these categories it falls into?




Jonathan's picture

Good point. I have always

Good point. I have always wondered about this and I suspect its really a pretty dodgy character that is only useful if you know what the plant is in the first place! That said, if the plant is very small and flowering it is probably an annual. Small perennials delay flowering till they are bigger. But, annuals can get big, so this is no good for those cases.

I do not know the key you refer to. Where can it be found?

University of Edinburgh and Biodiversity Observatory (OU)

Martin Harvey's picture

vegetative key

I put a bit about it on my blog:

but you're too late for the pre-publication offer now! See also:

Entomologist and biological recorder

james.heywood's picture

Fwd: Boundaries

That's interesting info. Will come in handy at my allotment!

dw5448's picture

Biennials and rootstocks

There is also the complication of something like foxglove that gives a basal rosette in one year and an infloresence in the next.

I guess that the key assumes that you can observe over an extended period. Sometimes the remains of previous flowers, fruits etc can give a hint as to survival for more than one year, as can a woody nature, or underground bulbs or rhizomes (bit destructive to find out though).

I agree that you can't just tell by looking on one occasion.

Kluut's picture


Size is of no use as a guide to a plant being perennial or annual - common foxgloves are short-lived perennials, often biennials. Lots of small-growing garden "weeds" are perennials, such as dead-nettles, dandelions, hawkweeds, and even chickweed is perennial to a degree.
At the other end of the scale, some annuals will make substantial plants - Himalayan balsam for instance (usually killed by winter weather).
In gardening terms, perennial weed implies difficult to eradicate, and that means some form of root-stock - such as some, but not all docks, thistles, dandelions, bindweed and nettles.

Kluut's picture

Artificial division

To large extent the division perennial- annual are gardening terms with so many exceptions that in the natural environment they are almost meaningless. Apart from very woody species there is also no realistic and consistent way to infallibly identify perennials.
In cultivation, many plants that flower from seed in their first year are perennials that are grown as annuals - pansies/violas and many bedding plants. Others are short-lived perennials - polemonium. Man also grows many biennials for food - brassicas and carrots for instance.
Many very fleshy plants are also perennial - tomatoes, impatiens are obvious examples.

Jonathan's picture

You are right about the

You are right about the confusioa and blurred boundary, but of course there are species that are only ever found as annuals. Many cornfield weeds such as poppies (although there are perennials poppies of course).

University of Edinburgh and Biodiversity Observatory (OU)