Flowers
Capitulum (Head)
A capitulum or head is a round to flat topped cluster of flowers
(inflorescence) containing many individual stalkless (sessile) flowers arranged
around a receptacle. It is similar to a spike that has been reduced in length.
Bracts when present often form an involucre surrounding the receptacle.
Sea holly
Eryngium tripartitum
Torch ginger
Etlingera elatior
Bracts
Receptacle
Involucre
Peduncle
Back to main
flower menu
Next
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
A capitulum or head in members of the composite family (Asteraceae) are
round or roundish and contain many stalkless (sessile) flowers arranged around
a receptacle. The heads can be made up of combinations of ray and disk
florets. Ray flowers have a strap-like petal while disk flowers are tubular.
Ray floret
Receptacle
Bracts
Peduncle
Back to main
flower menu
Disk floret
Back
Next
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
Ray florets are usually larger and showier than disk florets but each can have
both male and female parts. In a mixed head of ray and disk florets, the outer
ray florets are usually sterile or female only. Each floret has fused petals and
a pappus. Pappas are modified sepals of awns, scales or bristles.
Ray floret
Disk floret
Petal
Pappus
Back to main
flower menu
Ray florets
Disk florets
Style
Ovary
Zinnia
Back
Next
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
In Stokes’ aster , it is clear in the ray floret that what appears to be a single
petal is actually five petals fused together. This type of ray floret with five
defined “teeth” is termed ligulate. The pappas occur as bristles.
Ray florets
Disk florets
Ray floret
Disk
floret
ovary
Receptacle
Pappus
Stokes’ aster Stokesia laevis
Back to main
flower menu
Back
Next
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
Stokes’ aster also clearly shows another characteristic of the composite
family. This is the grouping of numerous bracts that subtend and surround the
flower head as an involucre.
Disk florets
Involucre
Ray floret
Bracts
Peduncle
Receptacle
Stokes’ aster
Back to main
flower menu
Back
Next
Back to
inflorescence menu
Stokesia laevis
Main menu
Flowers
Capitulum (Head)
The cone in purple coneflower is an
outgrowth of the bracts as spines. See the
disk flowers between the pigmented spines.
These differ from a pappas because they
arise from the receptacle rather than at the
base of the petals on each floret.
Bract (spine)
Disk floret
Purple coneflower
Echinacea purpurea
Receptacle
Back to main
flower menu
Back
Next
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
In some plants the pappus elongates and
acts like a parachute for wind dispersal of
the achene. This arrangement of specialized
sepals (pappas) and achene is called a
cypsella.
Cypsella
Pappus
Achene
Goat’s beard (Tragopogon)
Back to main
flower menu
Back
Next
Back to
inflorescence menu
Ovary
Main menu
Flowers
Capitulum (Head)
Flowering heads show centripetal flowering where the outer flowers open first
and the innermost flowers last. In the examples below, the innermost flowers
have yet to open.
Gerbera daisy (Gerbera)
Back to main
flower menu
Back
Next
Lavender cotton (Santolina)
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
Not all composite flowers have both ray and disk flowers. Some are comprised
of all ray or all disk flowers.
Ox eye daisy
(Heliopsis)
Lavender cotton (Santolina)
Dandelion (Taraxacum)
Zinnia
Ray and disk florets
Disk florets only
Radiate head
Back to main
flower menu
Discoid head
Back
Next
Ray florets only
Ligulate head
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
Within a species, a typical head of mixed ray and disk florets can show a
change to all ray florets as seen in sunflower.
Sunflower
Back to main
flower menu
Back
Next
Helianthus annuus
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
In Chrysanthemum you can see some of the diversity of colors, petal
types and ray / disk floret combinations selected for from breeders.
Pompon
Double
Semidouble
Single
Chrysanthemum
Back to main
flower menu
Back
Next
Dendranthemum morifolium
Back to
inflorescence menu
Main menu
Flowers
Capitulum (Head)
In Chrysanthemum ray floret petals can fuse to form “spoons”.
Spoon
Chrysanthemum
Back to main
flower menu
Back
Dendranthemum morifolium
Back to
inflorescence menu
Main menu