International Journal of Horticulture, 2017, Vol.7, No.22, 180-204
182
The Eastern Asiatic Centre:
(China, Japan). There are about 250 ornamental plant species (5%) derived from it.
Important ornamentals originated are peony (
Paeonia lactiflora
), royal lily (
Lilium regale
), China wisteria
(
Wisteria sinensis
), China aster (
Calliatephus chinensis
),
Sophora Tomentosa,
Day Lily (Hamerocallis) and
chrysanthemum.
Tropical African Centre:
There are about 160 species (3% garden plants) indigenous to this centre. Popular
ornamentals are
Sansevieria trifasciata,
African violet (
Saintpaulea ionantha
), and orchids.
The Caucasian Western Asiatic Centre:
This centre contributed around 150 ornamental plant species (3%) and
out of them, autumn crocus (
Colchicum speciosum
), crested gentian (
Gentiana septemfida
),
Pyrethrum
coccineum
and pin-cushion flower (
Scabiosa caucasia
) are popular.
The Central Asian Centre:
It covers about 130 ornamental plant species (2.5% garden plants). Some
commercially important species originated from this centre are water lily, tulip (
Tulipa kaufmanniana
) and other
tulip species (
T. fosteriana
,
T. greigii
).
The Australian Centre:
About 100 (2%) ornamental plants have been originated from this centre.
Bassaia
actinophylla
,
Eucalyptus, Casuarina, Callistemon
and
Acacia longiflora
are popular amongst them.
The South American Centre:
It accounts for about 600 ornamental plant species (12% garden plants). Popular
ornamental plants originated from this centre are
Anthurium, Calendula, Dieffenbachia, Philodendron, Gloxinia,
Caladium hybridum, Salvia splendens, Heliotropium arborescens, Verbena hybrida
and morning glory (
Ipomoea
alba, I. purpurea
and
I .tricolor
).
The Macronesian Centre:
It covers about 50 species; and dragon tree (
Draecena draco
), species of Aloe and
beautiful shrublet campanula (
Azorina vidalii
) have been originated from this centre.
3 Mode of Reproduction (De and Bhattacharjee, 2011)
Pollination means transfer of pollen grains from anthers to stigmas. There are three types of pollination found in
heterogamous plants; namely autogamy or self pollination, allogamy or cross pollination and geitonogamy.
3.1 Autogamy or self- pollination
It is defined as the transfer of pollen grains from anthers to stigmas within the same flower and always found in
hermaphrodite flowers. Self pollination results in the production of homozygous populations. Self pollinated
species show heterosis and do not show inbreeding depression. There are various types of mechanisms of self
pollination such as cleistogamy, homogamy and chasmogamy.
Cleistogamy:
In this case, the bisexual flowers do not open at all and ensure the complete self pollination. It
occurs in
Salpiglossis sinuata, Viola pubescens, Impatiens glandulifera.
Homogamy:
In this case, the anthers and stigmas of a bisexual flower mature at the same time and causes self-
pollination. It is found in
Lathyrus odoratus
, Lupin, Aster, Calendula.
Chasmogamy:
In this case, the flowers generally open only after the pollination is over. It occurs in pansy,
Clitorea ternatea
.
3.2 Allogamy or cross pollination
It is defined as the transfer of pollen from one plant to the stigmas in flower on a different plant. Such types of
pollination are brought out by air (Anemophilous), water (Hydrophilous), insects (Entomophilous) and animals
(Zoophilous).
Anemophilous ornamentals: Rhododendron, Azalea, Acacia
Hydrophilous ornamentals:
Salix alba, Euphorbia grantii
