There seems to be a widespread belief, especially in the US, that plants are either annuals or perennials depending on where you grow them. There are a lot of perennials that we usually grow as annuals, either because they do better in their first year, or because they aren't hardy in most gardens where they're grown, but that doesn't alter the fact that they are really perennials.

Given their perfect growing conditions, perennials will grow for several years. Given perfect growing conditions, annuals will die after they flower and set seed in their first year.

Here's a list of plants often considered to be annuals and usually grown for only one year, with their correct botanical classification according to the Royal Horticultural Society/American Horticultural Society A-Z Encyclopaedia of Garden Plants.

Annual

Perennial

Ageratum houstonianum - Floss Flower Ammobium alatum - Winged Everlasting Argemone mexicana - Mexican Prickly Poppy Asperula orientalis - Woodruff Borago officinalis - Borage Brachycome iberidifolia - Swan River Daisy Browallia americana Calendula officinalis - English Marigold Callistephus chinensis - China Aster Campanula medium - Canterbury Bells Centaurea cyanus - Cornflower, Bachelor's Buttons Clarkia amoena - Clarkia, Godetia Cleome hassleriana - Spider Flower Consolida ajacis - Larkspur Coreopsis californica Cosmos bipinnatus - Cosmos Cosmos sulphureus - Cosmos Felicia bergeriana - Kingfisher Daisy Felicia heterophylla Gaillardia pulchella - Blanket Flower Helianthus annuus - Sunflower Iberis umbellata - Candytuft Ipomoea coccinea - Red Morning Glory Ipomoea purpurea - Morning Glory Lathyrus odoratus - Sweet Pea Lavatera trimestris - Mallow Moluccella laevis - Bells of Ireland Nemesia strumosa Nemophylla - 5-spot Nicotiana langsdorfii - Flowering Tobacco Nigella - Love in a Mist Papaver rhoeas - Field Poppy Papaver somniferum - Opium Poppy Phacelia campanularia - Californian Bluebell Phlox drummondii - Annual Phlox Salvia viridis - Annual Clary Sanvitalia procumbens - Creeping Zinnia Schizanthus pinnatus - Poor Man's Orchid Tagetes - African or French Marigold Tithonia - Mexican Sunflower Torenia fournieri - Wishbone Flower Tropaeolum majus - Nasturtium Tropaeolum peregrinum - Canary Creeper Zinnia elegans - Zinnia

Antirrhinum majus - Snapdragon Arctotis fastuosa - Cape Daisy Arctotis venusta - Blue-eyed African Daisy Bellis perennis - English Daisy Browallia speciosa - Bush Violet Calandrinia grandiflora Campanula, most - Bellflower Catharanthus roseus - Vinca Celosia argentea - Cockscomb Cobaea scandens - Cup and Saucer Vine Craspedia globosa - Drumsticks Dianthus barbatus - Sweet William Dianthus chinensis Erysimum cheiri - Wallflower Felicia amelloides - Blue Daisy Gaillardia grandiflora - Blanket Flower Gaillardia aristata - Blanket Flower Gazania rigens - Treasure Flower Gerbera jamesonii - Transvaal Daisy Glaucium flavum - Yellow Horned Poppy Heliotropium arborescens - Cherry Pie Impatiens walleriana - Busy Lizzie Ipomoea alba - Moonflower Ipomoea lobata - Spanish Flag Lablab purpureus - Hyacinth Bean Limonium sinuatum - Sea Lavender Lobelia erinus - Trailing Lobelia Lophospermum erubescens - Creeping Gloxinia Matthiola incana - Stock Mimulus x hybridus cultivars Mirabilis jalapa - 4 o'clock, Marvel of Peru Nicotiana alata - Flowering Tobacco Papaver nudicaule - Icelandic Poppy Pelargonium - Geranium Pericallis x hybrida - Cineraria Petunia cultivars - Petunia Ricinus communis - Caster Oil Salvia splendens - Scarlet Sage Salvia, most species - Sage Solenopsis/Isotoma/Laurentia axillaris Solenostemon scutellariodes - Coleus, Flame Nettle Thunbergia alata - Black-eyed Susan Vine Verbena x hybrida cultivars - Verbena Viola x wittrockiana - Pansy

Perhaps part of the problem lies with the use of common names. Sometimes, some members of a genus are annuals, while others are true perennials. Perhaps using just a common name like Poppy or Sage and being familiar with only one or two members of the genus might lead you to suppose that all members of that genus are annual or perennial, whichever your local plant is. As you can see from the list, though, there are many plants that have both annual and perennials in the genus.

If you want to extend the range of plants in your garden, you can certainly try growing plants which aren't normally hardy over the winter in your area, and you might find some you thought were only annuals stay with you for more than one year. This isn't because you've changed an annual into a perennial, it's because you've managed to find the conditions which suit a plant which is, by nature, a perennial.

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Other entries with information on this topic

Common Names and the Latin names of some popular garden plants
Common Names Index - the common names of plants mentioned in these pages, with their Latin name
Latin Names - the meanings of some common Latin botanical names
Plant Families - an introduction to Plant Families