Although flowers do of course bloom throughout the growing season, the most famous displays of wildflowers occur in early spring before the deciduous tree leaves emerge. This enables forest flowers to photosynthesize, grow and reproduce before most of the sunlight is blocked by dense tree leaves. The degree to which this seasonal flush of flowering occurs depends on the type of forest canopy and its density, soil type, moisture, herbivory and other factors. But in north facing (damp) slopes with rich soil, the floral display can be absolutely amazing.
Certainly the trees and shrubs can also produce striking blooms and one of my favorites is the Fraser magnolia. It has an enormous single flower which is believed to be similar to the most primitive flower types. All of the magnolias, including cucumber trees and tulip poplars, produce nectar and/or fruit which is very attractive to birds.
A flower that appears in groups of large single blooms is the spectacular pink or pinxter azalea, a member of the heath family in the genus Rhododendron. The female stigma extends well beyond the male stamens, presumably a design to reduce inbreeding. The corolla tube is fairly broad and of intermediate length so that large pollinators such as bumblebees and hummingbirds can access the nectar and still come in contact with the anthers containing pollen.
The design of the fire pink is somewhat similar in that it seems designed to attract hummingbirds and butterflies, with a bright red color and an enlarged tubular corolla tube characteristic of the genus Silene. In contrast woodland phlox has an extremely narrow corolla tube which would seem to exclude any pollinators that do not have long thin tongues, presumably butterflies or sphinx moths. Yet bumblebees in our area of VA have learned to bite the base of the flower and steal the nectar without pollinating it.
The showy orchis, a type of orchid, attracts bumblebees with the bluish color of the hood (combined sepals and lateral petals) contrasted with the white lip. The Wake Robin, a type of trillium, has an entirely different strategy for pollination by emitting the scent of rotten meat to attract flies. The red buckeye flowers have no scent but are a brilliant red to attract hummingbirds.
The viburnums have adopted a strategy of massing tiny white flowers together. Two types in our yard are Maresii and Snowball which pose an interesting contrast since Maresii has many small flowers in the center of the inflorescence with enlarged infertile showy flowers around the outside to attract pollinators. This same design is found in the wild witch hobble bush. The Snowball variety has been artificially selected to have only the large showy flowers and thus cannot produce fruit since the showy flowers are sterile. So clearly if you want to attract birds with the fruit, you should plant the types that have fertile flowers.
The wide variety, color and shape of flowers truly is a remarkable tribute to the intensity of the reproductive drive. We can enjoy these remarkable objects at a simple level of the beauty that we perceive, or delve further into their specialized evolutionary design which is primarily to attract pollinators.