The northeastern United States belongs to the deciduous forest biome, and the plants you will find there fit the expectations for that environment. Plants have developed adaptations that allow them to withstand cold winters and then come to life fully for the summer. You won't find succulents, tropical plants or plants associated with the tundra and alpine environments, but you will find an array of deciduous trees, conifers and understory plants.
To begin learning more about the plants in your area, you should first acquire the reference materials needed to help you learn to make identifications. Field guides provide photographs or illustrations in addition to detailed descriptions and, often, information that helps you to narrow down what family or genus a particular plant belongs to. If possible, try to find a field guide that focuses on eastern or northeastern plants, such as Peterson's "Eastern Trees," to assist with identifying the Northeast's numerous tree species, or the Audubon Society's "Field Guide to North American Wildflowers, Eastern Region." Organizations like the New England Wildflower Society and the Connecticut Botanical Society offer online and print resources to aid in identification and classes on regional plant life.
Types of Plants
In the Northeast, plant identification necessarily involves identifying trees. Although part of the deciduous forest, northeastern forests also contain evergreen conifer trees, particularly as you move northward or into the higher elevations found in the region's mountains. Beneath these trees, small patches of sunlight filter through the canopy overhead and support understory plants, such as smaller trees, shrubs and wildflowers. Spring brings an eruption of ephemeral wildflowers --- short-lived flowers that grow and produce seeds in the brief window of time before the canopy leafs out and blocks their light.
When identifying conifers, the arrangement of the needles will provide the primary clue to the tree's identity. Pines have needles that occur in clusters. For example, the needles of the eastern white pine (Pinus strobus), a common resident in northeastern forests, grow in bundles of five. Needles that occur singly indicate a fir or spruce, with fir needles exhibiting a flattened shape. Cedars and junipers lack needles and, instead, have leaves covered in tiny scales.
Also note the tree's habitat. A species that grows in the mountains --- where soils tend to be dry and acidic and the climate colder --- may not grow on the coast. For example, the red spruce (Picea rubens), a species found almost exclusively in the Northeast, grows in mountainous habitats, while the northern white-cedar (Thuja occidentalis) prefers the wetter and less acidic soils of the lowlands.
Deciduous Tree Identification
Deciduous trees occur more widely throughout the Northeast, in both the mountains and lowlands. The leaves of deciduous trees also provide a primary clue to the tree's identity. The shape of the leaves, pattern of the leaf veins and shape of the leaf margins are all information you will use when learning to distinguish one deciduous tree from another. You should also note the arrangement of the leaves on the twig or branch. Some leaves occur in pairs directly opposite each other while others occur singly, alternating sides as they move down the branch.
Maples (Acer species) and oaks (Quercus species) dominate the northeastern forests. Both types of trees have lobed leaves, but maple leaves occur opposite each other, while oak leaves alternate on the branch. Leaves of the tuliptree (Liriodendron tulipifera) --- the Northeast's tallest deciduous tree --- resemble those of maple, but also alternate on the branch. Tuliptrees tend to occur at lower elevations, along with ash (Fraxinus species) and elm (Ulmus species). In mountain and lowland forests cleared by logging or fire, you're most likely to find poplars and aspens (Populus species), trees with oval- or heart-shaped leaves that tremble in the breeze.
Understory Plant Identification
The best clue to a flowering plant's identity is, of course, the flower, but because many Eastern species only flower for a brief period each year, you may have to rely on leaves and other clues here as well, using the same techniques used to describe the leaves of deciduous trees. When identifying flowers, the color, shape and symmetry, number of petals and structure of the flower --- whether it grows alone, in clusters or on spikes --- provide important information for identification.
As with trees, understory plants in the Northeast tend to prefer either the dry, acidic soils of the mountains or the moister, less acidic lowlands. In the mountains, you can expect to find an abundance of flowering shrubs, such as rhododendron (Rhododendron species) and laurel (Kalmia species), growing in the shade of larger trees. These shrubs tend to have thick, leathery evergreen leaves and showy pink and white blossoms. On the edges of the forest, you will find smaller trees like dogwood (Cornus florida) and sumac (Rhus species). Flowering plants found in the lowland forest include touch-me-not (Impatiens species), honeysuckle (Lonicera species) and viburnum (Viburnum species).