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Monday, July 4, 2011

Platanus x hispanica - London Plane Tree

London plane trees are one of the most commonly planted trees in CA and very common here in Santa Cruz. They have a long history as very tough landscape trees. When I asked a great friend and arborist why he thought they were so popular his response was "they are tolerant of just about anything".

They originated in England during the industrial revolution after European plant explorers brought together 2 species (P. occidentalis and P. orientalis) usually separated by thousands of miles of ocean. They proved to be very tough and tolerant of heavy particulate pollution commonly seen in London back in the day. This is one of my favorite plantings in Bath England.




London plane trees are large (70'+), bold with a very strong habit. Upright to pyramidal when young but becoming rounded with broad spreading branches. Habit really depends on the cultivar being grown. This is the planting on Walnut street in SC. These trees line so many streets. They close the canopy very nicely.



Leaves are alternate (6-8"), 3 to 5-lobed with light bristles on the lobes. Dark green upper surface with a pubescence on the lower surface that falls off fairly early in the season. A bit of an irritation to many.





Stems are brownish green, stout and slightly zig-zag. Buds are large and well hidden by the leaf base.



This is a young stem in summer and not really hardened off but you can see the small bud and the base of the petiole, which is hollow.




On young vigorous stems  you might see small leaf like appendages at the base of the petiole, they are called stipules. 




Flowers are monoecious in clusters, reddish coloring to the cluster pretty early in the spring.




Fruit is an aggregate, 1" diameter. They break up before falling usually but are still a mess. Generally borne in pairs. (Sycamores are single, plane trees in pairs)



As I mentioned, they are tolerant of almost anything and one is a special type of pruning called pollarding. You can see examples of them pruned like this at the Farm on Soquel Drive. These are from Filoli gardens.



These are in SF at the bandstand in golden gate park.




They are also likely to be damaged by a disease called Anthracnose which causes the leaves to brown and fall off early in the spring and continue later into summer. The tree will need to spend lots of energy to replace the leaves and it causes the plant to weaken over time. They also look sort of funky with most of the foliage out on the ends of the branches or they might develop what is called witches brooms.


This shows the canker where the fungal spores overwinter and provide the source of the fungal spores to infect the new leaves the following spring, when the rain splashes them onto the new leaves.




Several cultivars are available that are more resistant to anthracnose disease. 'Bloodgood' and 'Columbia' are commonly encountered. 'Yarwood has been planted in front of the new Cabrillo College bookstore, reportedly has single fruits and a very tight pyramidal habit. The native sycamore is very susceptible to this disease and should not be planted (sorry native tree lovers).

Here are a few others that I like, this one is in Canterbury England.



This one is from Amsterdam.



Can't recall the garden…. Canterbury as well I think….


Misidentification:
Not likely to be mistaken for another tree but perhaps the native sycamore, P. racemosa. This tree has very white bark when old, usually defoliated due to anthracnose disease and the leaves are more deeply lobed but not bristle tipped.

The tree is also known as P. x acerifolia and looks a lot like a maple leaf, especially Acer plantanoides, the norway maple.  Funny, there is also an Acer pseudoplatanus, the sycamore maple. So we have 2 maples that look like a sycamore and a sycamore that looks like a maple.

However, heard an interesting story about P. racemosa and P. x hispanica, they hybridize freely and it has been suggested that any California sycamore less than 150 years old is likely to have P. x hispanica in it. Might not be a bad thing considering the problem with anthracnose.

Location:
Almost everywhere.

Aptos:
Soquel Drive at Cabrillo College

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