Dandelions are so similar to catsears (Hypochaeris) that catsears are also known as "false dandelions". Both plants carry similar flowers which form into windborne seeds. However, dandelion flowers are borne singly on unbranched, hairless and leafless, hollow stems, while catsear flowering stems are branched, solid and carry bracts. Both plants have a basal rosette of leaves and a central taproot. However, the leaves of dandelions are smooth or glabrous, whereas those of catsears are coarsely hairy.
Other plants with superficially similar flowers include hawkweeds (Hieracium) and hawksbeards (Crepis). These are both readily distinguished by their branched flowering stems which are usually hairy and bear leaves.
See also: Flora, Online Flowers, Flower Arrangement