Instant Notes: Plant Biology

Section L – Reproductive ecology

L1 Ecology of flowering and pollination

Most flowers are hermaphrodite and perform two functions: disseminating

pollen to other flowers, and receiving pollen to fertilize their own ovules. These

functions involve slightly different adaptations. Here we consider a cross-

pollinating hermaphrodite plant; self-fertilizing plants are considered later and

unisexual flowers (Topic H2) have separated the functions. There is a selective

advantage for a flower to disperse its pollen as widely as possible to give it the

maximum chance of siring seeds. In its capacity as a female parent the flower

must receive enough pollen for maximal fertilization, but the plant must also

provide enough energy and nutrients for the formation of seeds and fruits.

The dual
function of
flowers

Key Notes

Cross-pollinating hermaphrodite flowers must disseminate pollen and

receive pollen from other flowers, these two functions involving different

adaptations. The functions are separated in unisexual flowers.

There is great variation in size and resource input into fruits and seeds by

different plants. In some the resources of the parent plant limit seed or

fruit set whereas in others the amount of pollination is limited. Many

plants are limited by a combination of factors.

Wind-pollinated plants produce large quantities of pollen. Pollinating

animals have different abilities to carry pollen with some more effective

than others. Some plants have precise adaptations for particular

pollinators. Pollen is deposited in decreasing quantity on the stigmas of

up to the next thirty flowers visited.

Once pollen has reached a stigma there may be competition between

pollen grains with some pollen tubes growing faster than others and

potentially complex interaction with the styles. There may be selective

abortion, particularly of selfed seeds.

Hermaphrodite flowers always have the potential for self-pollination and

some plants are habitually self-fertilized. Advantages of self-fertilization

are assured seed set, less resources needed for flowers and, after some

generations with high mortality, identical seedlings with no new

unfavorable combinations. Disadvantages are lack of variation allowing

no adaptation to changing environments or pathogen attack and

inbreeding depression. Inbreeding depression from self-fertilization is

manifest in nearly all plants studied at some stage in the life cycle.

Related topics The flower (D1) Polymorphisms and population

Breeding systems (H2) genetics (L4)

The dual function of

flowers

Seed and fruit set

The dissemination of

pollen

Self and cross

fertilization

Effective fertilization