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Double Flowers Double Flowers Flower morphology The strict definition of a double flower is where there is an increase in petals or petal-like structures in place of stamens and / or carpels. A fully double amaryllis (Hippeastrum). A semi-double rose (Rosa). Double Flowers Flower morphology The broader definition of double flowers would include those examples where any of the floral organs change identity or multiply. A petaloid carpel in begonia. Multiplying sepals in hydrangea. Double Flowers Floral organ replacement • Petals replace stamens (carpels) • Sepals replace petals (stamens) • Hose-in-hose Floral organ increase • Floral duplication • Increased sepal number • Increased bract number Inflorescence reorganization • Fertile to sterile florets • Disc florets to ray florets Double Flowers Floral organ replacement A flower can be viewed as consisting of concentric whorls of organs. Each whorl represents a different organ type. Double Flowers Floral organ replacement Floral identity is controlled by a series of homeotic genes. This has been described using the ABC model for gene interaction. Double Flowers Floral organ replacement Gene group A codes for sepals and petals. Double Flowers Floral organ replacement Gene group A codes for sepals and petals. Gene group B codes for petals and stamens. Double Flowers Floral organ replacement Gene group A codes for sepals and petals. Gene group B codes for petals and stamens. Gene group C codes for stamens and carpels. Double Flowers Floral organ replacement A typical homeotic mutation to produce a double flower involves replacement of stamens and carpels with additional petals. Double Flowers Floral organ replacement This type of mutation has been shown to be a loss-of-function mutation in the group C genes. Double Flowers Floral organ replacement - Stamens to petals Petaloid stamen Begonia (Begonia) showing a petaloid stamen. Note the yellow color typical of the anther is still present but nonfunctional on the small petal. This azalea (Rhododendron) flower has most of the stamens converted to petals. This flower will be male sterile. Double Flowers Floral organ replacement - Stamens to petals Petunia Double Flowers Floral organ replacement - Stamens to petals Peony (Paeonia ) Semi-double Single Full double Double Flowers Floral organ replacement - Stamens to petals Full double all stamens converted to petals Semi-double some stamens converted to petals Mock orange nicely shows the transition from a stamen to a petal that occurs in double flowers. Normal petal Filament petal-like Anther petal-like Normal stamen Anther Single no or few stamens converted to petals Mock orange (Philadelphus) Filament Double Flowers Floral organ replacement – Stamens to petals In Lenten rose (Helleboris ), the entire stamen (filament and anther) is converted to a petal-like structure. Double Flowers Floral organ replacement – Stamens to petals In Fuchsia, the anther portion of the stamen becomes petal-like and the filament remains unchanged. Double Flowers Floral organ replacement - Stamens to petals In some instances, the filament of the stamen becomes petal-like. Lily (Lilium) Geranium (Pelargonium) Double Flowers Floral organ replacement - Stamens to petals Double flowering in Daylily (Hemerocallis ) involves widening of the stamen filament into a petal-like structure. Double Flowers Floral organ replacement - Stamens to petals The complete transformation of the stamen filaments to broad petallike structures, it is often termed an Anemone type double flower. Double Flowers Floral organ replacement - Stamens to petals Hollyhock (Alcea) Rose-of-Sharon (Hibiscus) Double Flowers Floral organ replacement - Stamens to petals The corona is a crown-like structure that forms between the stamen and petal whorls in daffodil (Narcissus ). In double flowering daffodil flowers, the corona and stamen filaments become petal-like. Corona Double Flowers Floral organ replacement - Stamens to petals Corona Daffodil (Narcissus ) Double Flowers Floral organ replacement - Stamens to petals In some species, petals are no longer produced and their function is replaced by petal-like stamens called staminodes. Double Flowers Floral organ replacement - Stamens to petals Plants in the ice plant family (Mesembryanthemaceae) do not have petals. Their role is taken by the showy, strap-like staminodes. Staminodes Staminoids Staminodes Fertile stamens Fertile Fertile anther stamens Fertile anthers Ice plant (Carpobrotos) Dayflower Living stones (Commelina (Lithops)) Double Flowers Floral organ replacement – Sepalody In some species, petals are no longer produced and their function is replaced by petal-like sepals called sepalodes. Double Flowers Floral organ replacement – Sepalody Sepals replacing and taking the pigmented role of petals. Sepals Sepals Four-o’clock (Mirabilis) Windflower (Anemone) Double Flowers Floral organ replacement – Sepalody (stamens to sepals) Anemone flowers do not have petals – only petal-like sepals. Therefore in double flowers, the sepals replace stamens. Anemone Sepals Double Flowers Floral organ replacement – Sepalody (stamens to sepals) Staminodes are a natural transformation of stamens to petal-like structures. In Clematis, these become more petal-like in double flowers. Clematis Staminodes Single flower Double flower Double Flowers Floral organ replacement – Sepalody (stamens to sepals) Clematis can also completely replace the staminodes, stamens and sepals with petal-like structures. Single Staminodes and stamens Staminodes, stamens and sepals Double Flowers Floral organ replacement - Sepalody In rose, the sepals are normally leaf-like. When sepals multiply and replace the petals, it produces a rosette of leaf-like flower heads. Floribunda rose Rosa chinensis ‘Viridiflora’ Double Flowers Floral organ replacement - Sepalody In Dianthus, the sepals and bracts are linear, leaf-like structures. In the double flowering ‘Green Ball’ sweet William, the sepals and bracts multiply and replace petals, stamens and carpels. Sweet William (Dianthus barbatus) Dianthus barbatus ‘Green Ball’ Double Flowers Floral organ replacement – Stamens to tepals When the petals and sepals are not distinguishable, they are called tepals. Autumn crocus (Colchicum) Double Flowers Floral organ replacement - Stamens to tepals Tulip (Tulipa ) Double Flowers Floral organ replacement – Hose-in-hose Hose-in-hose is when the sepals or stamens are converted to an extra set of petals that creates two whorls of identical petals that fit one inside the other. It apparently refers to the old English habit of men wearing pairs of long stockings (hose) one inside the other (hose-in-hose). Azalea (Rhododendron) Double Flowers Floral organ replacement – Hose-in-hose When pulled apart, you can see two the two whorls of duplicate, funnel-shaped petals. Azalea (Rhododendron) Double Flowers Floral organ replacement – Hose-in-hose Angel’s trumpet (Brugmansia) Single flower Double hose-in-hose flower Double Flowers Floral organ replacement – Hose-in-hose Bellflower (Campanula) Canterbury bells Single flowers Double hose-in-hose flower Double Flowers Floral organ replacement – Hose-in-hose Columbine (Aquilegia ) produces a flower with petals modified into a spur. Double flowering columbine produces many whorls of short spurred stamen derived, petal-like structures in a multiplied hose-in-hose pattern. Petal Sepal Petal spur Double Flowers Floral organ replacement – Hose-in-hose The origin of the extra petals can be seen in this illustration from Master’s book on “Vegetable Teratology”. Double Flowers Floral organ replacement – Hose-in-hose In this blue version, the columbine flower has 4 or more whorls nested inside each other. In soft pink double columbine has the common name ‘Granny’s Bonnet’. Double Flowers Floral organ increase Columbine (Aquilegia ) also produces a spur-less double flowering form that appears to be iterative whorls of petal-like stamens. Double Flowers Floral organ replacement – Fibonacci series Double Flowers Floral organ replacement – Fibonacci series The spiral patterns of initiating petals in double flowers (like many other patterns in nature) can be described as a Fibonacci series. Double Flowers Floral organ replacement – Fibonacci series The previous pair of numbers sum to the next number in the series. The series is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 … Sundial seashell Spirals of disc florets in Purple coneflower (Echinacea). Double Flowers Floral organ replacement – Fibonacci series As illustrated here in this camellia flower, there is actually one set of spirals in a clockwise direction and one set in a counter-clockwise direction. Double Flowers Floral organ replacement – Fibonacci series Petal spirals in a double flower follows a numerator and denominator set of offset Fibonacci numbers. 1/2, 1/3, 2/5, 3/8, 5/13, 8/21, 13/34 … A 2/5 spiral A 3/8 spiral Double Flowers Floral organ replacement – Fibonacci series A 1/3 spiral 3 0 2 1 Double Flowers Floral organ increase • Floral duplication • Increased sepal number • Increased bract number Double Flowers Floral organ increase - Floral duplication The stamen number converted to petal-like structures partially defines the degree of doubling, but there can also be additional multiplication. Ranunculus Double Flowers Floral organ increase - Floral duplication In a fully double flower, all stamens are converted to petals. Ranunculus Double Flowers Floral organ increase – Floral duplication Grape hyacinth (Muscari ) ‘Blue Spike’ Double Flowers Floral organ increase – Floral duplication Purple coneflower (Echinacea) Double Flowers Floral organ increase - Sepals Snowflake oakleaf hydrangea (Hydrangea quercifolia ‘Snowflake’) produces florets with sepals that continue to multiply as the season progresses. June July Double Flowers Floral organ increase - Bracts Increased bract number in Bougainvillea Double Flowers Floral organ increase - Bracts Increased bract number in poinsettia (Euphorbia pulcherima) ‘Christmas Rose’ Double Flowers Floral organ increase - Bracts Members of the aroid family produce a specialized bract called a spathe that forms a hood or base for the inflorescence (spadix). In calla lily (Zantedeschia), the spathe can double by simple multiplication of the bract. Spathe Double Flowers Floral organ replacement The hydrangea inflorescence can have sterile florets with large sepals, fertile florets with large sepals, or fertile florets with reduced sepals. Sterile florets with large sepals Fertile florets with reduced sepals Fertile florets with large sepals Double Flowers Floral organ replacement When all the fertile florets are converted to showy sterile florets, it is considered a form of doubling. Hydrangea arborescence Fertile flowers Sterile flowers Smooth hydrangea (Hydrangea arborescence) Double Flowers Floral organ replacement Doubling in oakleaf hydrangea (Hydrangea quercifolia). Double Flowers Floral organ replacement The same doubling pattern of replacing fertile florets with showy sterile florets can be seen in a number of Viburnum. Sterile florets Fertile florets Sterile florets European cranberry viburnum (Viburnum opulus) Double Flowers Floral organ replacement Members of the composite family (Asteraceae) can be made up of combinations of ray and disk florets. Ray flowers have a strap-like petal while disk flowers are tubular. Ray floret Receptacle Peduncle Bracts Disk floret Double Flowers Floral organ replacement Ray florets are usually larger and showier than disk florets, but each can have both male and female parts. Ray floret Disk floret Petal Pappus Ovary Ray florets Style Zinnia Disk florets Double Flowers Floral organ replacement There can be a different ratio of ray to disc florets depending on the species. Ray and disk florets Mostly ray florets All disk florets Double Flowers Floral organ replacement When a species with a typical inflorescence of mixed ray and disk florets makes a change to all ray or all disk florets it is considered a form of doubling. All ray florets Sunflower (Helianthus annuus ) Double Flowers Floral organ replacement There have been several cultivar selections in Purple coneflower (Echinacea purpurea) for an inflorescences with all ray florets. Double Flowers Floral organ replacement There have been several cultivar selections in Purple coneflower (Echinacea purpurea) for an inflorescences with all ray florets. Double Flowers Floral organ replacement In shasta daisy (Leucanthemum), there are semi-double and full double cultivars. ‘La Spider’ ‘Real Glory’ Double Flowers Floral organ replacement Zinnia has disk florets with extended lobes. They completely disappear in the fully double ray floret inflorescence. Disk florets Double Flowers Floral organ replacement Gaillardia is an example of a composite genus where the disk florets replace the ray florets to present an interesting set of doubles. Double Flowers History The first double flowers described in ancient literature are references to roses in Europe and Asia. Theophrastus (~ 250 BC) and Pliny (~1 BC) both have descriptions of double roses. Double Flowers History References to double flowering tree peonies (“Moutan”) date back to 750 AD in China. Double Flowers History Rosa centifolia is one of the popular rose cultivars in Elizabethan Europe. Double Flowers History The Rose Window was incorporated in European cathedrals as the Gothic architectural style developed in the 12th Century. Double Flowers History Rose window at Notre Dame in Chartres, France dates to the 12th Century. Rose window at Notre Dame in Paris, France dates to 1225. Double Flowers History Ranunculus Georg Ehret 1746 Double Flowers History The “Double Striped Camellia” appeared in Curtis’s Monograph on the Genus Camellia, 1819. Double Flowers History Flowering stocks (Matthiola incana) is an interesting double flowering plant because it is grown from seed and the seedlings segregate about 50/50 for single or double plants depending on cultivar. Double Flowers History Plants can actually be selected in the seedling stage as eventually being single or double flowering plants. After seedling emergence, the growing temperature can be reduced by about 10oF and the color of the seedlings noted. Dark green seedlings will be single. Light green seedlings will be double. Single Double Double Flowers History Double flowers appear prominently as subjects in 17th Century still life paintings. Jan de Heem 1660 Double Flowers History In this still life of cut flowers there is inclusion of a vista out the window to suggest that the flowers are part of a greater world of God’s divine creations. The flower images are a reminder that nature is beautiful, but eventually decays with time. Earthy beauty is fleeting and care needs to be taken for one’s spiritual well-being. Jacob van Walscapella - 1681 Double Flowers History The comparison of a flower with the transient nature of beauty and life is a general theme in the Golden Age of Dutch painting. Francois Desportes - 1715 Double Flowers History This painting makes the same point about the fleeting nature of life, but is not very subtle. Jan van Kessel 1665 Double Flowers History Double flowering columbine (Aquilegia) – Hose-in-hose Double Flowers History Poppy (Papaver) has a symbolic association with death, and rebirth. However, it does not completely explain why most poppy portraits only show the backs of the flowers. Jean Prevost 1805 Double Flowers History Poppy (Papaver) in still life paintings. Nicolaes Lachtropius - 1680 Jan Van Os - 1790 Double Flowers History The reason appears to be related to the shame involved in poppy being used as a secret message in a Royal assassination. The message was relayed by the removal of the poppy fruit that resembles a Royal crown.
