Forms of Flowers

• Even seemingly ordinary flower forms like sunflowers have some important distinctions. Jupiterimages/Photos.com/Getty Images

  Flowers like daisies and roses often typify what people think of as flower forms: a single blossom with petals arranged radially around the pistil and stamens. Flowering plants comprise the most extensive and diverse division of plants on Earth today, according to the University of Arizona's Tree of Life project. In addition to daisies and roses, flowering plants include species, such as grasses and oak trees, that produce atypical flower forms, and flowers like sunflowers and pea plants also assume shapes distinct from some of their more typical brethren.

Catkins

• Catkins dangle from trees as long, worm-like strands. Male catkins produce pollen, while female catkins develop strings of tiny and usually nonshowy flowers that eventually develop into seeds. Catkins usually develop in the spring and drop from the trees in late summer or autumn for overwintering and germination the following spring. While most catkins use wind pollination, some rely on insect pollinators, according to the University of British Columbia Botanical Garden. Trees that produce catkins include oaks, birches and alders.

Composite Flowers

• Flowers like sunflowers resemble the ordinary flower form but actually demonstrate a composite form: a single "flower" contains dozens or even hundreds of tiny flowers. Composite flowers are the most familiar in North America, according to naturalist Jim Conrad of Backyard Nature. The bumpy centers of composites consist of many tiny flowers, each one producing a single seed. A ray of petals surrounds the collection of tiny flowers at the composite's center. Composites include such familiar examples as the dandelion, sunflower, aster and thistle.

Racemose Flowers

• Racemose flowers include diverse shapes, but all racemose flowers include clusters of multiple florets that grow upward from a stem. Spikes, like gladiolus, include multiple florets emerging along a single stem. Racemes appear similar, but the florets each blossom from short stems emerging from the central stem. Snapdragons are familiar garden racemes. Corymbs and umbels include florets on multiple stems that extend to the same height, producing a flat arrangement of multiple florets that, unlike composites, are not unified on a single receptacle or enclosed by a single set of petals. Queen Anne's lace, yarrow and dill all produce flowers in these forms, but perhaps the most familiar racemose flowers occur right in your own backyard. The shaggy tops of grasses going to seed are actually flower spikes.

Papilionaceous Flowers

• Many flowers belonging to the legume family -- a classification including pea plants and vetch -- display an atypical shape known as the papilionaceous form. These flowers have a single, large petal at their tops called the banner, and two pairs of smaller petals known as the keels and wings, which enclose the flower's stamens. This shape causes nectar to pool at the bottom of the flower, increasing access to the flower by pollinators such as hummingbirds.