Sycamore tree allergy (Platanus) – a quick guide w/ photos.

green foliage with star shaped leaves and several dark brown balls hanging

In this article, we will learn to identify Sycamore or Planetrees (scientific name: Platanus) as well as how and when their pollen spreads.

Sycamore or Planetree (Genus: Platanus)Pollen allergy profile
Pollen seasonSpring
Pollination typePrimarily wind-transported. Each tree produces a large amount of pollen.
Cross-reactivity with other pollenOnly the trees within the genus Platanus e.g. London Planetree, American Sycamore, Western Sycamore, etc.
Pollen sourceMale flowers on the tree that look like small greenish-yellow berries.
GenderMonoecious: Each tree has both male and female flowers.
BarkThe brownish-grey peeling and flaky bark show creamy white under surface (see pictures below)
LeavesStar-shaped with generally five lobs and coarse toothy edges
FruitGreen furry balls, slightly bigger than a golf ball, that turn yellow and brown upon maturation.

How to identify a Sycamore tree or Planetree(Platanus)?

The three primary characteristics of a sycamore tree are:

  1. It’s creamy-white bark with light brown scales that for some species become knobby as the tree ages.
  2. A star-shaped leaf, generally, with five lobs and coarse toothy edges, which looks a lot like a maple leaf.
  3. Golf-sized, furry, yellow-brown fruit that hangs from long thin stalks.

The leaves are green during spring and summer but turn yellow during autumn before falling off. The leaves also show white fungus towards the autumn. The fruit stays on the tree through winter, but some trees may not be mature enough to have fruit.

A tree with green foliage, one star shaped green leaf, one yellow and orange star shaped leaf, two golf ball like brown fruit and a peeling brown-grey-white bark.
Platanus tree can be easily identified by its scaly peeling brown bark with a grey and white undercoat, a star-shaped leaf with five lobes, and golf-ball-sized yellow-brown fruit.

Platanus tree can be easily identified by its scaly peeling brown bark with a grey and white undercoat, a star-shaped leaf with five lobes, and golf-ball-sized yellow-brown fruit.

Bark and trunk

The tree bark is creamy-white with light-brown scales. The young tree’s trunk is straight but the older tree trunks become a bit knobby and branch out at around 6 to 8 feet. The trunk can have a diameter of 1 to 4 feet at the human eye level.

a cylindrical creamy white tree trunk with brown scales.
Western sycamore (Platanus racemosa)
a knobby grey brown tree trunk
London planetree (Platanus acerifolia)
a patchy white bark with brown scales of Sycamore tree.
London planetree (Platanus acerifolia)


Sycamore trees can grow up to 75 feet tall but are trimmed to lower heights in the cities. The trunk is 1 to 4 feet in diameter at the human eye level. The canopy could be pyramidal, round, or vase-shaped.

An oval shaped green tree
Sycamore (Platanus) tree. A pyramidal canopy.
A vase shaped green canopy of Sycamore tree.
Sycamore (Platanus) tree. A vase-shaped canopy.


The male and female flowers appear in spring. The female flowers are small furry purple spheres hanging in groups of two or three. The male flowers, on the other hand, are greenish-yellow.

Both male and female flowers are the size of a large peanut when young. The female flower matures into the larger golf-sized fruit after fertilization.

two purple furry blueberry-sized female flowers and below them are hanging three yellowish-green, same-sized and furry male flowers
Purple female flowers and yellow-green male flowers side-by-side on a sycamore during the spring bloom.
three purple colored furry balls hanging from a tree branch.
Sycamore female flower: The furry threads are the female pistils.
A greenish yellow furry ball with streaks of bright yellow attached to a small twig.
Sycamore male flower. The yellow streaks in furrows are pollen it holds.

How to know if Sycamore trees are releasing pollen?

The tree generally produces pollen before leaves start to emerge in the spring. The tree often looks bare, but by the time the four week long pollen cycle completes, the tree is quite lush with leaves.

A bare tree with mostly grey branches with a spreading canopy, about 25 feet tall.
Sycamore tree in early spring when it releases pollen. It looks pretty bare because new flowers and leaves have just started to appear.
a close up of a tree branch with a few yellow green leaves but several small furry ball like flowers hanging from the branches.
A close up of a Sycamore tree in the middle of spring bloom. Notice male and female flowers hang like little furry balls.

During which months do Sycamore trees release pollen?

Sycamore tree allergies are spring phenomena. In Northern California, the Sycamores release pollen between March-15th and April-15th. On the East coast of the US, where the spring arrives a little later, the pollen could be expected from April-15th to May-15th.

The tree releases pollen for three to four weeks during spring. Depending on the weather, the pollination window can shift each week. If you suffer from sycamore allergies, it is best to learn about the tree and its pollen-producing habits.

However, if you live in the San Francisco Bay Area, you have an easier way out! I do regular tree inspections and air sampling in the area to provide reliable pollen updates on our website

How does Sycamore pollen spread?

The sycamore tree releases its pollen in the air and wind can carry the pollen many miles. Inhaling the pollen is what causes the allergies.

Since the tree is widely planted on the West Coast as well as the East Coast, it is fair to expect its pollen to be airborne during spring in the entire United States.

Sycamore trees have a short pollination cycle that rarely goes past four weeks.

What does sycamore pollen look like?

On a slightly windy day during spring, one can see sycamore pollen as yellow dust coming off the tree. However, each individual grain is invisible to the naked eye.

The Sycamore pollen grain is around 20 micrometers (0.02 mm) with three short furrows. The furrows have warty structures. Platanus pollen: Small, 20 microns, three short furrows with verruci.

A smooth cornered triangular pollen with white corners which represent furrows that do not stain pink like the rest of the pollen.
Sycamore/Plane tree pollen at ~400x magnification.

To see the pollen of other plants and trees, visit our pollen library.

Sycamore allergy summary

Sycamore/Planetree (Genus: Platanus) releases pollen during spring but does so for a short period of three to four weeks. Sycamore tree allergies are not as common as are allergies from the other spring bloomers such as Ash, birch, oak, cypress, and junipers.




  1. Allergy Plants by Mary Jelks, M.D.
  2. Plant identification terminology by James G. Harris and Melinda Woolf Harris (Second Edition)
  3. Sampling and indentifying pollens and Molds by E. Grant Smith

All pictures, unless otherwise credited to another source, are taken by the author and are copyrighted material. The pollen picture is taken in our aerobiology lab using an Olympus compound microscope.

Sudhir Setia

Sudhir is certified by the National Allergy Bureau (NAB) as a pollen counter and identifier. He has been living with Hay Fever for nearly 30 years and studies allergens at his aerobiology lab.

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