The Lacecap varieties have some similarities to : Guelder-rose which also has large sterile flowers on the outside and smaller fertile flowers on the inside, and spread out as a flattish pancake, but the flowers are creamy white instead.
Uniquely identifiable characteristics
Distinguishing Feature :
The reader is much more likely to find it growing in a garden than growing wild; indeed, your Author has never seen it growing wild. There are a great many cultivated varieties that can be purchased from garden centres, many attempting to enhance one colour in favour of the others.
Hydrangea macrophylla has long been cultivated in Japan and China, being introduced into Europe only in 1790. It is a deciduous shrub which grows in a dome shape up to 2 or 3m high. The macrophylla in the scientific name refers to the large leaves, which can reach 16cm in length. The flowerhead is in the form of a corymb, either flattish as for Lacecap Hydrangeas (which are fertile) or hemispherical for Mophead Hydrangeas, which are sterile. The smaller flowers on the Lacecap have five petals, whereas for the Mophead it is usually only four (but the above photos show five in some specimens). In both types the large flowers have four sepals with a much smaller central flower.
The colour of the flowers varies a great deal, from red, pink, mauve, blue, purple and violet, the colour depending upon both the pH of the soil, and the availability of soluble aluminium in the soil.
The aluminium increases the blueness of the flowers, especially under alkali conditions. Gardeners soimetimes put Aluminium Sulfate on the soil in order to get bluer blooms, however soluble aluminium can be poisonous to some trees.
Hydrangea also has the ability to tolerate normally toxic aluminium in the soil, in fact it not only tolerates it but hyperaccumulates the aluminium.
There is also a Climbing Hydrangea which can also grow wild.
Hydrangeas are poisonous containing cyanogenic glycosides amongst several other poisonous secondary metabolites.
Isocoumarin is not as ubiquitous in the natural world as is its fellow isomer Coumarin, shown here for comparison only; it has no presence in Hydrangea. The two oxygen species have merely swapped positions. Isocoumarin itself may or may not be present.
The main compounds present in Hydrangea macrophylla are based upon Isocoumarin, or to be more precise, 4-hydroxyphenyl-isocoumarin, which has many similarities to the flavones such as Quercetin, which is also a chromenone. Indeed, the 4-hydroxyphenyl-isocoumarines are also Chromenones, absorbing light in the visible spectrum being therefore coloured. Quercetin itself is not said to be a constituent of Hydrangea.
The two main isocoumarins within Hydrangea macrophylla are
Phyllodulcin and possibly
Macrophyllol. The 8-O-Gylucosides of these isocoumarins are also present which are sweet.
Phyllodulcin is very sweet itself (between 400 to 800 times sweeter than
Sucrose aka Sugar), and is used as a sweetener in pharmacology, lacking any diabetic effects. Both Hydrangenol and Macrophyllol are also sweet, but not as sweet as Phyllodulcin.
There seems to be great confusion over
Macrophyllol; entirely different structural formulae seem to have the same 'Macrophyllol' name! They are named after plants belonging to different Genera whose second scientific name ends in 'macrophylla'. This happens quite a lot, which is why chemical names for molecules are preferred.
Thunberginol A is present in the leaves.
Thunberginol B and
Thunberginol F (below) are present in a cultivated variety of Hydrangea called Hydrangea macrophylla var. thunbergii.
8-O-GLUCOSIDES of ISOCOUMARINS
Hydrangea macrophylla also has the 8-O-Glucosides of Hydrangenol and of Phyllodulcin, of which only the Hydrangenol glucoside is shown. The 8-O-Glucoside of Phyllodulcin has the red glucose unit attached to Phyllodulcin in a similar way at position 8 (shown in green) on Phyllodulcin.
Hydrangenol-8-O-glucoside and Phyllodulcin-8-O-glucoside are sweet, and are also present in
Thunberginol F is said to be present in both Hydrangea macrophylla and Hydrangea macrophylla var. thunbergii but this is not an isocoumarin as are the other Thunberginols, it is a
benzofuran: note how a carbon atom has moved out of one of the six-membered rings leaving the 5-membered furan ring in comparison to the Thunberginols above.
ANTHOCYANINS & METALLOANTHOCYANINS
Delphinidin is the pH-sensitive anthocyanidin present in many blue flowers, including Hydrangea. It is blue in basic conditions and red/pink in acidic conditions. The pH sensitivity is not the only reason that the flowers of Hydrangea vary from pink to mauve to blue to violet. The colour of Hydrangeas are also sensitive to the level of aluminium salts in the soil. The aluminium is able to form complex salts called metalloanthocyanins. The metalloanthocyanins are supramolecular complexes with metal ions, 3-O-glycosides of anthocyanins and flavones in stoichiometric amounts and which self assemble themselves. The 3-O-glycoside of Delphinidin, which is present in Hydrangeas, is called Myrtillin. By forming complexes with Myrtillin aluminium can intensify the blue colours of the flowers on Hydrangeas. All sorts of colours are possible varying from red, mauve, purple, violet and blue.
For another Metalloanthocyanin see Cornflower.