"Double-flowered" describes varieties of
flower
Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...
s with extra
petal
Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...
s, often containing flowers within flowers.
The double-flowered trait is often noted alongside the
scientific name
In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...
with the abbreviation ''fl. pl.'' (''flore pleno'', a
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
ablative
In grammar, the ablative case (pronounced ; abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages. It is used to indicate motion away from something, make comparisons, and serve various o ...
form meaning "with full flower"). The first abnormality to be documented in flowers, double flowers are popular varieties of many commercial flower types, including
rose
A rose is either a woody perennial plant, perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred Rose species, species and Garden roses, tens of thousands of cultivar ...
s,
camellia
''Camellia'' (pronounced or ) is a genus of flowering plants in the family Theaceae. They are found in tropical and subtropical areas in East Asia, eastern and South Asia, southern Asia, from the Himalayas east to Japan and Indonesia. There are ...
s and
carnation
''Dianthus caryophyllus'' ( ), commonly known as carnation or clove pink, is a species of ''Dianthus'' native to the Mediterranean Basin, Mediterranean region. Its exact natural range is uncertain due to extensive cultivation over the last 2,00 ...
s. In some double-flowered varieties all of the reproductive organs are converted to petals. As a result, they are sexually
sterile
Sterile or sterility may refer to:
*Asepsis, a state of being free from biological contaminants
* Sterile (archaeology), a sediment deposit which contains no evidence of human activity
*Sterilization (microbiology), any process that eliminates or ...
and must be propagated through cuttings. Many double-flowered plants have little wildlife value as access to the nectaries is typically blocked by the mutation.
History
Double flowers are the earliest documented form of floral abnormality, first recognized more than two thousand years ago.
Theophrastus
Theophrastus (; ; c. 371 – c. 287 BC) was an ancient Greek Philosophy, philosopher and Natural history, naturalist. A native of Eresos in Lesbos, he was Aristotle's close colleague and successor as head of the Lyceum (classical), Lyceum, the ...
mentioned double roses in his ''Enquiry into Plants'', written before 286 BC.
Pliny also described double roses in 1st century BC. In China, double
peonies were known and selected by around 750 AD, and around 1000 AD double varieties of roses were cultivated to form the
China rose (one of the ancestors of modern
hybrid tea rose
Hybrid tea is an informal horticultural classification for a group of garden roses. The first hybrid tea roses were created in France in the mid-1800s, by cross-breeding the large, floriferous Garden roses#Hybrid perpetual, hybrid perpetuals with ...
s). Today, most cultivated rose varieties bear this double-flower trait.
Herbalists of the Renaissance recognized double flowers and began to cultivate them in their gardens—
Rembert Dodoens
Rembert Dodoens (born Rembert van Joenckema, 29 June 1517 – 10 March 1585) was a Flemish people, Flemish physician and botanist, also known under his Latinization (literature), Latinized name Rembertus Dodonaeus. He has been called the father o ...
published a description of double flowers in 1568, and
John Gerard
John Gerard (also John Gerarde, 1545–1612) was an English herbalist with a large garden in Holborn, now part of London. His 1,484-page illustrated ''Herball, or Generall Historie of Plantes'', first published in 1597, became a popular garde ...
created illustrations of many double flowers beside their wild-type counterparts in 1597. A double-flowered variety of
Marsh Marigold was discovered and cultivated in Austria in the late 16th century, becoming a valued garden plant.
The first documented double-flowered mutant of ''
Arabidopsis
''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organ ...
'', a model organism for plant development and genetics, was recorded in 1873. The mutated gene likely responsible for the phenotype, AGAMOUS, was cloned and characterized in 1990 in
Elliot Meyerowitz's lab as part of his study of molecular mechanisms of pattern formation in flowers.
Genetics of double-flower mutations
Double-flower forms often arise when some or all of the
stamen
The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10
Morphology and terminology
A stamen typically consists of a stalk called the filament ...
s in a flower are replaced by
petal
Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...
s. These types of mutations, where one organ in a developing organism is replaced with another, are known as
homeotic mutations. They are usually
recessive
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...
, although the double flower mutation in
carnation
''Dianthus caryophyllus'' ( ), commonly known as carnation or clove pink, is a species of ''Dianthus'' native to the Mediterranean Basin, Mediterranean region. Its exact natural range is uncertain due to extensive cultivation over the last 2,00 ...
s exhibits
incomplete dominance
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...
.
In ''
Arabidopsis
''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organ ...
'', which has been used as a model for understanding flower development, the double-flower gene AGAMOUS encodes a protein responsible for tissue specification of stamen and
carpel
Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more ...
flower segments. When both copies of the gene are deleted or otherwise damaged, developing flowers lack the signals to form stamen and carpel segments. Regions which would have formed stamens instead default to petals and the carpel region develops into a new flower, resulting in a recursive
sepal
A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106
Etymology
The term ''sepalum'' ...
-petal-petal pattern. Because no stamens and carpels form, the plants have no reproductive organs and are sexually sterile.
Mutations affecting flower morphology in ''Arabidopsis'' can be described by the
ABC model
The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower. There a ...
of flower development. In this model, genes involved in flower formation belong to one of three classes of genes: A class genes which affect sepal and petal formation, B class genes which affect petal and stamen formation, and C class genes which affect stamen and carpel formation. These genes are expressed in certain regions of the developing flower and are responsible for development of organs in those regions. Agamous is a C class gene, a
transcription factor
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...
responsible for activating genes involved in stamen and carpel development.
Gallery
Image:Bridal_pink_-_morwell_rose_garden.jpg, Most garden rose
A rose is either a woody perennial plant, perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred Rose species, species and Garden roses, tens of thousands of cultivar ...
s are double-flowered
Image:Lilac.head.600pix.jpg, Double-flowered lilac
''Syringa'' is a genus of 12 currently recognized species of flowering woody plants in the olive family or Oleaceae called lilacs. These lilacs are native to woodland and scrub from southeastern Europe to eastern Asia, and widely and commonly ...
, often called "French lilac"
Image:Double-flowered_Camellia.jpg, Double-flowered Camellia
''Camellia'' (pronounced or ) is a genus of flowering plants in the family Theaceae. They are found in tropical and subtropical areas in East Asia, eastern and South Asia, southern Asia, from the Himalayas east to Japan and Indonesia. There are ...
Image:Gartennelke_1.jpg, Double-flowered carnation
''Dianthus caryophyllus'' ( ), commonly known as carnation or clove pink, is a species of ''Dianthus'' native to the Mediterranean Basin, Mediterranean region. Its exact natural range is uncertain due to extensive cultivation over the last 2,00 ...
s
Image:DOUBLE_PINK_PATUNIA.jpg, Double-flowered petunia
''Petunia'' is a genus of 20 species of flowering plants of South American origin. The popular flower of the same name derived its epithet from the French, which took the word , 'tobacco', from a Tupi–Guarani language. A tender perennial plan ...
Image:Paeonia_officinalis_officinalis0.jpg, Double-flowered peony
The peony or paeony () is any flowering plant in the genus ''Paeonia'', the only genus in the family Paeoniaceae. Peonies are native to Asia, Europe, and Western North America. Scientists differ on the number of species that can be distinguish ...
Image:Kanzan, Cerasus lannesiana 'Sekiyama' Koidzumi.JPG, Double-flowered ''Prunus'' 'Kanzan'
References
{{DEFAULTSORT:Double-Flowered
Flowers
Plant morphology