In my opinion the best wildflower identification guide is Newcomb’s Wildflower Guide. It enables you to identify plants even if the flower is not present. Most guides have lovely photos of the flowers but are not helpful in the times of the year when the flower is absent.
Let’s imagine that you see this plant.
The first thing to do is examine the flower closely. (You obviously cannot do this if the flower is not present. More about that later).
This flower is actually made up of a multitude of small flowers and we cannot determine how many petals it has as you would with a wild rose.
Our flower is classified by Newcomb as a flower with “parts indistinguishable”.
In the Newcomb system this puts the flower in category #8.
Next we have to determine if the leaves are opposite to each other as they are in maple
or alternate on the stem. Our plant has alternate leaves and is #3 in the Newcomb system.
and finally does the plant have no apparent leaves, leaves which are entire (no teeth or lobes), leaves which are toothed or lobed, or leaves which are divided like these ash leaves.
Our plant has extremely deeply lobed leaves which Newcomb puts into the “divided” category #4.
In the Newcomb system our plant is an 8 / 3 / 4. These types of plants are located from page 424 – 430 in the guide.
It is very clear that our plant has prickly leaves.
This puts it on page 430 Plants with Prickly, Deeply Lobed Leaves; Flowers in Large Heads
Thistles: A group of plants well known because of their spiny leaves and large flower heads.
We are on the right track but there are 8 thistle species on page 430. These each show various criteria.
Is the flower head 1″ or less high as in this Canada Thistle bloom?
Our flower is larger. Are the leaves white-woolly beneath?
Though the leaf does have whitish hairs underneath, the basic colour beneath is green not white.
Are the stems prickly below the leaves?
The stem is prickly below the leaves.
Our plant is Bull Thistle (Cirsium vulgare). There is a similar plant called Nodding Thistle but it has flower heads which are bent over.
If the plant you wish to identify does not have a flower when you see it, determine if the leaves are opposite or alternate and determine if the leaves are entire, have teeth or lobes or are divided. Then look at the plants that have these characteristics in all of the various flower types in the guide. Eventually you should find your plant.