Daisy
Flowers: Daisies are probably the most successful group of plants in the
world. Daisy is the accepted common name for members of the Asteraceae family.
The old name for this family was Compositae. World wide there are 1100 genera
with 25,000 species. In Australia there are 205 native genera with 970
species. As well as these native daisies there are many introduced species
that have become weeds and naturalized.
The conventional daisy flower is really an
inflorescence known as a capitulum, which is composed of many individual
flowers. There are two types of flower. The flowers on the circumference are
usually bright and showy and are known as ray florets. These florets are
usually sterile and their purpose is to attract pollinators (usually insects).
In the centre of each capitulum there is a large number of inconspicuous
flowers. These are known as disk florets and are perfect flowers. Disk florets
produce seeds. Mature seeds have sepals reduced to bristles, hairs or barbed
spines known as pappus. Pappus are the hairy appendages seen on mature daisy
flowers such as dandelions. They aid seed dispersal. In this case the seeds
are light and are readily dispersed by wind. The seeds of those species with
barbed spines are dispersed by hitching a ride in the fur of animals or on
human clothing. The efficiency of seed dispersal, by daisies is the major
reason for the successful spread of introduced daisies in Australia.
The
upper image is a capitulum and the lower is an individual disk flower.