Drosera flowers/pollination/hybrid questions

ANTSPlantation

Carnivorous Plant Addict
I don’t know what my plants are up to lately because they really seem to do weird things such as this: for some reason, a sundew grew out of the flower stalk of a sundew.
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I am not sure I would try this out because I am a purest as many of you know but am just curious if anyone has tried it? Might be an interesting thing for someone to try. I've siffed through the internet and can not find any documentation on this hybrid even if it does exist somewhere.
 
Yes, it has been done, e.g. see here:
D. capillaris "Pasco Giant" x rotundifolia 'Charles Darwin'
More common is the hybrid D. capillaris x intermedia. Maybe interesting for purists: This sterile natural hybrid was found in Pender Co., NC (see CPN Sept.1987). It was shown on the front cover of CPN in June 2003. What is known as D.capillaris "long arm" from Tate's Hell S.F., FL is probably the allopolyploid hybrid (shown in CPN 32, too).
According to some reports there are more capillaris hybrids: The backcross D.intermedia x capillaris "long arm" was made, too. Different crosses of D. anglica x capillaris were made, also one using the long arm form, i.e. a complex cross: D. (linearis x rotundifolia) x (capillaris x intermedia). D. linearis x capillaris was made as well. More man made hybrids are D. brevifolia x capillaris, D. capillaris x oblanceolata, D.tokaiensis x capillaris (i.e. D. (rotundifolia x spatulata) x capillaris) and D. esmeraldae x capillaris.
 
When the development of an inflorescence is disturbed the result can be shocking and fascinating. At the same time quite a few lessons about nature can be learned.
But first, what should a normal flower look like? Look at the following picture of D.filiformis from Nova Scotia:
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Flower scheme of D.filiformis Shelburne Co., NS

It consists of 4 whorls of special flower organs. At the base there is the calyx, a whorl of 5 special, small, green leaves, each of which is called sepal (look at the green cup at the base of the flower in the following picture). Together with the 5 pink petals (collectively called corolla) they form the showy (non-reproductive) part of the flower called perianth which attracts pollinators. The picture on the right shows the reproductive parts of the flower: The next whorl is consists of 5 stamens, that point towards the centre. They shed the (yellow) pollen at their ends from the anthers and thus form the male part. The female part of the flower and final stage is the pistil. It consists of 3 carpels that are fused at their base forming the ovary (the future seed capsule). The ovary is topped by 3 forked styles that have stigmas at their end (the place the pollen needs to go).

While flowers look wonderful complicated and can do an amazing job, they are just the tip of the growth axis. For the stem (peduncle) of the inflorescence the internodes are widely separated, sometimes bearing tiny leaves (bracts); within the flower the internodes are highly compressed. The flower parts (sepals, petals, stamens, carpels) can be regarded as extremely modified leaves (foliar theory). J. W. von Goethe developed this point of view (later called homeosis (Bateson, 1894)), in “The Metamorphosis of Plants”, already in 1790 (Or if you like poetry, in form of an elegy). Goethe mentions the umbrella like style of Sarracenia and emphasises that it is green just like a leaf. He was inspired by abnormal flowers, like a rose that continues the growth of the stem directly from the centre of a flower. He also considered a form of Ranunculus asiaticus with filled flowers. Here the carpels are developed into petals while the stamens are unaltered.

Such flowers with many extra petals are very popular, e.g. double-flowered roses. Sometimes multi-petaled cultivars are placed into sub-categories like:
semi-double (part of the stamens turned into extra petals)
double (most or all stamens converted into petals)
filled (most or all stamens and carpels converted into petals)
There is Pinguicula primuliflora “Rose” that has several extra corolla layers derived from the pistil: Whole plant (R.Buttery), flower side view
Sarracenia with rosulate flowers (stamens and carpels transformed into extra sepals/petals) are also well known, e.g. a S.purpurea ssp.purpurea f.plena was described from Yarmouth Co., Nova Scotia in 1955 having rosulate flowers without stamens or pistil. It might have looked like this (G.Hunt).
Or S.leucophylla “Tarnok” which is a well known cultivar that retains some stamen and can even set seed: Cross section (H.Snocken). This clone has double flowers genetically fixed (inherited). In some other plants it occurs randomly, caused by environmental factors, e.g. here one of my plants with extra petals (transformed stamens):
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S.rubra ssp.viatorum “antho-free” Taylor Co., GA with double flowers

I don’t know any inherited, double-flowered Drosera yet, but abnormal flowers with missing sepals or petals (common in smaller or weak plants), or extra petals, stamens or carpels are not rare, e.g.:
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left to right:
1. D.filiformis NS with 2 reduced petals
2. D.filiformis NS with 1 missing petal (darker pink colour)
3. D.filiformis Columbus Co., NC with 6 instead of 5 petals and stamens, 4 instead of 3 carpels/styles
4. D.tracyi Franklin Co., FL with 9 petals, 7 stamens, 4 carpels (most likely as a result of fasciation)

Several genes responsible for the development of the flower organs were found. The ABC(DE) model proofed useful (Haughn and Somerville, 1988) and is still being refined and transferred from Arabidopsis to other genera. Sepals are developed by expression of A-class genes, petals by co-expression of both A- and B-class genes, stamens need the co-expression of B- and C-class genes, and carpels require the expression of C-class genes only. So double flowers (petals instead of stamen and sepals instead of carpels) are often caused by mutations of C-class genes. Normal leaves are being formed instead of flower organs e.g. if the expression of all 3 gene classes is halted.

Abnormal development of a leaf-like floral part instead if a sepal, petal, stamen, or carpel is called phyllody. This condition may be found in genetic mutants or caused by plant pathogens (like an infection by virus or phytoplasma).
There are some more names (in floral teratology) for related abnormal growths:
virescence, i.e. green petals without changed form, e.g. seen in green tulips (“viridiflora”)
frondescence, i.e. phyllody of many floral parts
chloranthy, i.e. a complete form of frondescence, e.g. seen in Rosa chinensis 'Viridiflora', which is a special kind of double-flowered rose with leaf-like petals.

This is an example of D.filiformis from NS with leaf-like parts (including the tentacles) instead of petals. The other floral parts (sepals, stamen, carpels) are normal:
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D.filiformis Shelburne Co. , NS showing phyllody of the petals

In literature and on the web there are many other examples of CP-flowers with leaf like parts, sometime plantlets developing within the inflorescence. This is frequently, not quite accurately, called “false vivipary” within the CP-community.
True vivipary would be if a seed or embryo starts growing into a plant while still attached to the plant. This is constantly seen in some mangroves (like Rhizophora mangle) that grow in intertidal, saline swamps. Or in Escobaria vivipara, a cactus growing as far north as Canada that will tolerate some frost, that has seed germinating still inside the fruit. These plants improve reproduction success this way.
The terms false vivipary / pseudovivipary or vegetative apomixis are used if generative propagation is not involved, e.g. if plantlets develop within an inflorescence from the (somatic) tissue. These are clones of the of the mother plant. This may happen from buds within the inflorescence that grow into plants (e.g. Drosera prolifera or Chlorophytum comosum) and is a way of spreading, i.e. vegetative reproduction analogous to the division of the rhizome. Analogous to leaf cuttings, plantlets may sometimes grow from other parts of the flower.

This phenomenon of Drosera flowers developing leaf-like structures is known for quite a while. Some were described formally as forms, variety, or subspecies. But many of them are not accepted, mainly because the characters on which the descriptions are based are not unique or constant enough.

A D.rotundifolia found by Lyngby in Denmark was described as var.bracteata (in “Haandbog in den danske flora” by Lange, 1850). It had a forked inflorescence (panicle) and obovate sepals with tentacles (phyllody of the sepals is easily missed because they usually are already green). A very different and extremely disjunct, tropical D.rotundifolia from New Guinea was named ssp. bracteata (Kern and van Steenis, 1955) because it had slightly different sometimes leaf-like bracts (ligulate, glandular-denticulate). But this may be found occasionally in temperate D.rotundifolia as well. The tropical D.rotundifolia are different, however. The plants from Mindanao (Philippines) that I grow have smaller greenish leaf blades, reddish petioles, the dew is less sticky, and they never produce any hibernacula. These plants never showed phyllody of the bracts or sepals. A plant that shows extreme phyllody of both is a D. rotundifolia from the mountains of the Mediterranean island Corsica. Those plants were described having often leaf-like bracts. Maire called it f.corsica (1904) and suggested it might be on its way to become a species. Briquet (1910) presented more details and drawings what he calls var.corsica, showing a plant with forked scape, leaf-like bracts, and cleistogamous flowers with sepals consistently having tentacles at their tip. While extremely forked scapes, small flowers, and leaf-like bracts are very frequent in cultivated plants from Corsica and Tuscany, sepals showing phyllody are sometimes found, but rare. The flowers do open as usual. This variety is not sharply separated from the typical form since there is also the normal type of D.rotundifolia present at those sites and single plants like var.corsica sometimes found also in other countries.
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Another peculiar variety of D.rotundifolia called var.comosa was described by Fernald in 1905. He found small D.rotundifolia with sepals, petals and carpels being transformed into a rosette of glandular foliage-leaves while botanising on the Gaspé Peninsula in QC. There were many of these plants (clones, because the plants were sterile) that probably spread by those plantlets over an area of half an acre. Similar plants were found, e.g. in Charlotte Co., NB, or Oneida Co., NY, and could possibly (rarely) occur anywhere. Here one of those flowers from the type herbarium sheet:
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Flower of D.rotundifolia var.comosa (HUH #42392)

Planchon gave an in depth report on a similar observation of an unusual D.intermedia earlier, already in 1848: The calyx was described as normal, petals and carpels as leaf-like. Here some interesting drawings:
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Fig.6: A chloranthic flower of D.intermedia. Normal sepals, abnormal tentacle bearing leaf-like petals, and leaf-like carpels. There are two tentacle-like structures at their tip in stead of styles and the ovary is exposed bearing gland-tipped structures instead of ovules.
Fig.15: This is a more complex structure in place of an ovule. There are all kinds of transitional forms from fused gland-tipped hairs, some forming a cup, some looking almost like a normal, but not fully closed ovule, some look more like a tiny leaf. The example shown here resembles a Nepenthes pitcher. The stalked hollow sphere has an opening with a tiny leaf-like structure on top. Inside a small bud is starting to develop.
Fig.12: Vegetative apomixis: A plantlet is developing from the centre of an abnormal glandulous structure of the leaf-like carpel.

A flower in many aspects comparable to what Planchon observed was shown by Rice here.

Rice posted a another interesting picture of D.anglica in Oregon that developed carnivorous leaves within the flower. This is possibly a case similar to the flower mutation of D.filiformis from NS.

Levine described an observation of D.intermedia from Ocean Co., NJ in 1916 (“Further observations on chloranthy in Drosera intermedia”): All flower organs except the stamens were modified into leaf-like structures: Carpels replaced by a rosette of leaves like in a hibernacula. Those developed later into plantlets.
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Left: D.intermedia with chloranthic flower, right: drawing of the flower at an older stage

There are similar sightings for D.intermedia, e.g. from Killbear Park, ON.
Another example of a chloranthic flower developing into plantlets was reported for D.x hybrida from Burlington Co., NJ by J.Ksepka:
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flower, plantlets developing from flower, hibernacula forming

In conclusion, there are different reasons for abnormal flowers. Some may just be caused by environmental stress or a disease. Some develop plantlets within the inflorescence or even within the flower itself. In other cases just some floral parts are replaced by tentacle bearing leaf-like structures. The more interesting examples are genetically fixed and may give some insight how the flower development works. The latter might be fascinating cultivars worth growing. Keep your eyes peeled and you'll might find some examples in the field or among the plants you grow at home.

Short list of selected references:
Coen and Meyerowitz (1991) The war of the whorls. Nature 353, 31-37
Goethe (1790) Die Metamorphose der Pflanzen. Gotha
Haughn and Somerville (1988) Genetic control of morphogenesis in Arabidopsis. Developmental Genetics. 9, 73-89.
Jabbour et al. (2015) Ranunculacean flower terata. Flora 217, 64-74
Levine (1916) Chloranthy in Drosera. Botanical Gazette 62, 389-399
Masters (1869) Vegetable Teratology. London (273-280)
Meyerowitz et al. (1989) Abnormal flowers and pattern formation in floral development. Development 106, 209-217
Planchon (1848) Sur la famille des Droséracées. Ann.Sci.Nat.Bot.Ser.3, 83-89
 
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Fantastic research! I love seeing this stuff, especially about a local plant that doesn't seem to have much information on it published. Not that I can find anyway, so this is amazing!

Do you work in the field?
 
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