For a quick identification of a perennial, you can always try asking a neighbor or a professional horticulturist at a local nursery. But learning the unique characteristics of each family of flowers offers a rewarding pastime. It's a bit like a game of 20 questions, each one getting you closer and closer to an answer. Flower characteristics are the basis for most identification, since unrelated plants can have similar leaf forms.
Monocots and Dicots
The main division of flowering plants is between monocotyledon and dicotyledon. Monocots have flowers with petals in multiples of three; dicots have petals in fours or fives. Monocots also tend to have leaves with veins that run parallel to each other, while dicots have leaves with netted veins. A lily flower and a sword-like iris leaf will give you a fairly good picture of an average monocot. Dicots have a variety of forms, but a single rose blossom and a maple leaf provides the general idea.
To identify a plant, note whether the petals are fused together into a tube or free and individual. Take a look at the stamens and the pistil, the male and female organs at the center of the flower. The sepals are usually green, petal-like structures llocated below the petals, but may be colored. The more unusual the flower shape, the simpler it is to identify.
Learning The Families
Some families of flowers have distinctive shapes. The pea family, for instance, all have similar asymmetrical blossoms. Most plants in the daisy family have the typical daisy bloom with many tiny disk flowers surrounded by ray flowers. Those in the mustard family have petals in four or multiples of four. The celery family tends to have heads of tiny flowers in flat clusters. The rose family has simple blossoms of five petals in the classic single rose form.
The shape and arrangement of leaves is helpful in narrowing down your choices. Perennials have leaves that sprout each year from lasting root systems. Note whether the leaves are strap-shaped, palmate--like a hand with fingers--finely cut and ferny, round or oval. Also examine the edges, which can be serrated or smooth.
Other Characteristics To Note
The time that you find a perennial in blossom can help you narrow down your choices. For instance, a tall perennial with pink single rose flowers in fall could be a Japanese anemone, but if you find it blooming in spring would be another flower entirely. A particular scent to the leaves could tell you that the plant is an onion or something in the mint family. Since so many perennials come in various shades, color may not be a reliable factor but add it to your list of characteristics.