INFLORESCENCE

Learning outcome:

i. To define inflorescence.

ii. To identify the parts of an inflorescence.

iii. To differentiate inflorescence from simple

flower.

iv. To compare determinate and indeterminate

inflorescence.

v. To describe the types of inflorescence.

• Some flowers do not appear solitary in a stem.

They are generally arranged in a fixed pattern we

call inflorescence.

• An inflorescence may be defined as a cluster of

flowers, all flowers arising from the main stem

axis or peduncle.

• Flowers included in the inflorescence are

generally called florets.

• Inflorescences with youngest flower at the end of

the main axis (rachis) are called "indeterminate"

(i.e. terminal bud continues to produce new

flowers).

• Inflorescences with oldest flower at the end of the

main axis are called "determinate" (i.e. terminal

bud stops growing and lateral flowers are

produced from axillary buds.)

Inflorescences can be:

Single: when all the flowers are gathered in the

same single pattern.

Compound: when a complex pattern is made of

another single patterns.

Main single inflorescences

1. Raceme - Florets are attached along a floral

peduncle with stems similar in length. Young

florets appear above and old ones below.

2. Spike - Inflorescences similar to racemes, but florets

are attached directly to the floral peduncle,without

stems.

3. Corymb - All the florets are arranged along a

floral peduncle but, differently to racemes, stems

have different length in such a way that all the

florets appear at the same flat round level. Each

flower stem originates from different point on the

main stem. Outer flowers opens first.

4. Umbel - Florets arise from the same point of the

peduncle.

5. Head / Capitulum - Florets bearing no stem are

gathered together on a platform-shaped peduncle.

This is the inflorescence characteristic in the daisy

family.

Ray floret

Involucre Disc floret

6. Cyme - a central flower opens first and later

flowers are borne on branches below it. Some

cymes are one-sided (scorpioid cymes)

7. Catkin - a pendulous inflorescence, made up of

many small stalkless flowers.

8. Spadix - a thick, fleshy spike of unisexual,

apetalous flowers, often surrounded by a vase-

shaped or funnel-like modified leaf or spathe

which is often brightly colored. The male flowers

are typically clustered above the female flowers

on an erect, phallus-like spike.

Main compound inflorescences

1. Panicles - formed by several racemes

gathered together.

2. Compound umbels - formed by several

umbels gathered together.

Primitive traits Advanced traits

• Flower parts many

• Flower parts of an indefinite

number

• Flower parts free

• Flower parts spirally

arranged

• All types of flower parts

present

• Flowers bisexual

• Ovary superior

• Flower of regular symmetry

• Flowers conspicuous

• Ovules exposed

• Flower parts few

• Flower parts of a definite

number

• Flower parts fused

• Flower parts whorled

• Some types of flower parts

missing

• Flowers unisexual

• Ovary inferior

• Flower of irregular symmetry

• Flowers inconspicuous

• Ovules enclosed

FLOWER EVOLUTION