The Asteraceae is the largest family of vascular plants on the earth with over 1000 genera and 20,000 species worldwide. There are 2500 species alone in North America. The family is easily recognized by clusters of flowers sitting on a head or receptacle. What appears to be a single flower is actually clusters of many small flowers, called ray flowers and disk flowers. The disk flowers grow in the center and the ray flowers around the outside. Some species like chicory and dandelions have only ray flowers, thistles have only disk flowers and species like sunflowers have both types. The lobes of the ray flowers are longer, expanded to resemble a single petal, and are called rays. The receptacle is covered on the outside with several bracts, together forming an involucre. A tuft of fine hairs or bristles, called pappus, often grows from the top of the fruit. This may enlarge into a plume of hairs to aid in wind dispersal. The fruits themselves are dry and hard, a type known to botanists as achenes.
Guide to Identify Presented Species of the Composite Family
FLOWERHEADS WITH RAYS
Sunflower group A very large group of perennial or annual plants from many genera.
Flowerheads grow individually and have yellow or orange rays.
Disk flowers are arranged in a distinctive head in the middle.
Aster group A very large group of perennial or annual plants from many genera.
Flowerheads grow individually and have white or pink to blue or purple rays.
Disk flowers are arranged in a distinctive head in the middle.
Dandelion group Plants of this group usually contain milky juice.
Flowerheads have ray flowers only and often seeds with large, feathery plumes.
Genera included are Dandelions, Salsify, Chichory, Lettuce and Hawkweeds.
Group with small rays, heads in dense clusters Mostly perennials with small flowerheads, growing in dense clusters.
Flowerheads have both small rays and disk flowers in the middle.
This group includes Goldenrods, Yarrow, Snakeweed and Tarweed.
FLOWERHEADS WITHOUT RAYS
Thistle group Mainly tall, robust plants with spines on flowerheads, stalks and leaves.
Flowerheads are usually purple, and may be covered by spiny hooks.
This group consists of Thistles, Burdocks and Cocklebur.
Pussytoes group Small plants, often with male and female flowers on separate heads or plants.
Flowerheads small, usually white, in very dense, round or flat-topped clusters.
Large group, including Pussytoes, Cudweed and Pearly Everlasting.
Sagewort group Often tall or slender, aromatic plants growing in dry areas.
Flowerheads numerous, very small, in dense, tall and narrow clusters.
This group includes Sage, Sageworts, Mugworts, Ragweeds and Sumpweeds.
Group with yellow disk flowers Plants with no ray flowers and disk flowers which are yellow.
Flowerheads are compact or more loose, growing individually or in clusters.
Plants included are Tansy, Rabbitbrush, Horsebrush, Groundsel and Costmary.
Group with disk flowers of other colors Plants with no ray flowers and disk flowers which are blue to purple or white.
Flowerheads are growing individually or in open to dense clusters.
This group includes Knapweed, Blazingstar, Dusty Maiden and Coneflower.
Alphabetical listing with links to presented species of the Composite family:
