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Ivy classification - the Pierot system

Numerous ivy cultivars

Ivy needs to be classified because it has a marvellous ability to undergo what are known as "mutations". In other words, it can produce new shapes or colors. Often it's a simple stem that's not like the others. In this case, all you have to do is cut it out and multiply it. Sometimes, it's a new shape discovered in nature. In this way, new varieties of ivy are born spontaneously, which we can select and multiply.

The result is a huge number of cultivars. Probably between 1,000 and 2,000. Their number is difficult to establish, as not all cultivars offered by nurserymen around the world are necessarily referenced. In addition, there are many cultivars with different names, but which are actually the same. The Royal Horticultural Society's (unfortunately out-of-print) book, "Hedera The Complete Guide" by Hugh McAllister and Rosalyn Marshall, lists over 2000 cultivars, including synonyms.

A classification of ivy: the Pierot system

To help you find your way among all these ivy varieties, a classification system has been created by Suzanne Warner Pierot, founder and first president of the AmericanIvy Society. This system is based mainly on leaf shape. It has the advantage of being simple and easy to read. However, as nature is often more complicated than our simplistic human classifications, the same cultivar may be classified in several categories.

The Pierot system consists of 9 categories:

  • Adult ivies - All ivies that have progressed from their juvenile climbing stage to the ultimate shrub stage with flower and fruit production.
  • Bird's foot ivies : these are ivies whose leaves are composed of very narrow, deep lobes, like bird's feet.
  • Curly ivies: refers to ivies whose leaves are not flat, but wavy, curly, folded or hemmed.
  • Fan ivies - Fan ivy: ivy with broad, fan-shaped leaves.
  • Heart-shaped ivies - Lierres en forme de cœur: ivy with a heart-shaped leaf base.
  • Ivy-ivies - Type iv y: refers to all ivies that have retained the typical shape of common ivy, flat leaves with 3 to 7 lobes.
  • Miniature-ivies - Miniature ivies: ivies with small leaves, usually less than 2.5 cm long.
  • Oddities - Curiosities : ivy whose leaves take on original, unusual shapes.
  • Variegates ivies - variegated ivies: Ivies whose leaves are tinted with multiple colors.

As you can see, this ivy classification system is very accessible, even for the uninitiated. That's what has made it so successful. Created in the early 1970s, it is still very much in use today.

But, as you'd expect, ivy can also be variegated and curly, or miniature and bird's-foot. In such cases, it's best to indicate the major classification and complete with the secondary classification(s).

Hedera helix 'Palmata Adult'
adult ivy
Hedera helix 'Goldfinch'
Bird's-foot ivy
Hedera helix 'Boskoop
Curly ivy
Hedera helix 'Cockle Shell'
Ivy fan
Hedera helix 'Obovata
Heart-shaped ivy
Hedera helix 'Jake'
Miniature ivy
Hedera helix 'Erecta'
Curiosities
Hedera helix 'Ceridwen'
Mixed ivy
Hedera helix 'Chicago'
Ivy type

Pittsburgh ivy

Among all the mutations that ivy has offered us, there is one that has been particularly successful. It's a mutation selected by Paul Randolph in Pennsylvania. It is unique in that it is highly branched, generating stems emerging from each leaf axil, unlike many other ivies which form long stems with very few branches. This particular ivy was named 'Pittsburgh'. 

Another very interesting feature of this cultivar is its strong tendency to mutate, forming what botanists call "sports" (i.e. mutations). This has resulted in a number of new cultivars derived from 'Pittsburgh', to the point where it can be considered a tenth category in the ivy classification. These are ivies with a bushy, dense habit.

Hedera helix 'Pittsburgh'
Ivy classification - Pittsburgh Ivy

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