Agriculture Reference
In-Depth Information
parts. For example, the chrysanthemum used for cut
flowers (
Chrysanthemum morifolium
) is in the genus
Chrysanthemum
and is the
morifolium
species; note
that the genus name begins with a capital letter, while
the species has a small letter. Other examples are
Ilex
aquifolium
(holly),
Magnolia stellata
(star-magnolia)
and
Ribes sanguineum
(redcurrant). The genus and
species names must be written in
italics
, or underlined
where this is not possible.
Plants within a species can vary genetically in the
wild, giving rise to a number of naturally occurring
individuals with distinctive characteristics, much as
people vary in their appearance. Where these differ
significantly from the original species they may be
given an additional name after the species name and
are called a subspecies (subsp.), varietas (var.) or forma
(f.) depending on the degree of difference (forma
being the least different and subspecies the most).
These extra names are written in botanical Latin and
are italicized. They follow the species name, beginning
with a small letter and with the category abbreviated
and unitalicized in front of them - for example,
Hydrangea petiolaris
subsp.
anomala, Ceanothus
thyrsiflorus
var.
repens, Primula sieboldii
f.
lactiflora
.
In addition, cultivation, selection and breeding
by humans have produced variations in species
referred to as
cultivated varieties
or
cultivars
,
which are distinguished from naturally occurring
variants because they have not usually arisen in the
wild and must be maintained in cultivation either
by specific breeding programmes to produce seed
or by vegetative propagation. The cultivar is given
a name, often chosen by the plant breeder who
produced it, such as
Rhododendron arboreum
'Tony
Schilling' or
Cornus alba
'Sibirica', and is always a
non-Latin (vernacular) name, unitalicized and enclosed
in single quotation marks. Cultivar names can also
provide information about a plant's characteristics,
for example, a dessert apple that is suitable for
small gardens, 'Red Devil', produces bright red fruit;
a thornless blackberry, 'Loch Ness', was raised in
Scotland and shows considerable winter hardiness.
This information is useful for gardeners.
Penstemon
and
Pelargonium
genera have the cultivars 'Apple
Blossom', which describe well the pale pink and white
of the flowers. Cultivar names can also be written,
where applicable, after a common name, often for
fruits and vegetables - for example, tomato 'Ailsa
Craig' and apple 'Bramley's Seedling'.
The general term 'variety' (which is not the same as
'varietas' described above) is often used to refer to
any plant type which varies from the original species.
As such, it is frequently used interchangeably with
'cultivar'. In this publication, however, the correct term
'cultivar' will be used throughout.
A
cultivar
is a variation within a species that
has usually arisen and has been maintained in
cultivation. A horticultural
variety
is a general,
non-botanical term for plants that vary from the
species.
Examples of plant groupings and how they are named
in the family Rosaceae are shown in Figure 4.7.
Plant groups of importance in
horticulture
Gymnosperms and angiosperms
4
Two of the most significant groups in the plant
kingdom, the angiosperms and the gymnosperms, are
distinguished from all other plants by their reproductive
behaviour. These are the seed-bearing plants which
spread by dispersal of seeds rather than by spores as
in more primitive plants such as mosses and ferns.
Gymnosperms
characteristically produce male and
female cones which bear only partially enclosed
'naked' seeds, hence the name 'gymnosperm'. By far
the largest gymnosperm group is the
conifers
, which
include many hundreds of species such as the pines,
junipers, spruces and yews (Figure 4.8) and form the
vast boreal forests of the northern hemisphere. They
are also found in Australia, Papua New Guinea and
South America. The Chilean pine or monkey-puzzle
tree (
Araucaria araucana
) was once widely planted
in Victorian gardens. Conifers have the following
characteristics:
X
primarily perennial, woody trees and shrubs
X
have male and female cones
X
male cones produce prodigious amounts of pollen
which is spread by the wind
X
seeds, which are borne on female cones
X
often found in a limited range of habitats where
water is in scarce supply either due to low rainfall or
because the ground is frozen for much of the year
X
frequently display structural adaptations to reduce
water loss, for example, needles or scale leaves
(Figure 4.9) and branches designed to shed snow
X
may contain resin in their wood which acts as an
antifreeze
X
mostly evergreen to take full advantage of the
short growing season and avoid expending
unnecessary energy on producing new leaves each
year, although a few genera such as
Taxodium
,
Metasequoia
and
Larix
are deciduous.
