Mulberry pollen allergy (Morus) – a quick guide w/ photos.


three serrated yellow, green leaves on a tree trunk of Mulberry tree

In this article, with the help of photos, we will learn about mulberry pollen allergy (Genus: Morus). Also, we will learn how and when their pollen spreads.

Due to its hardiness, white mulberry grows all over the US. The red mulberry on the other hand grows mostly east of Texas.

Mulberry tree allergy facts and figures (Morus)

Mulberry tree allergy profileMorus
Pollen seasonSpring
Pollination typeWind-transported; releases abundant pollen in the air, which travels well with the wind because of its smaller size.
GenderGenerally dioecious: Male and female flowers grow on separate trees. Only male trees are responsible for pollen allergies. (Monoecious species do exist but they are an exception)
Cross-reactivities with other pollenOnly among mulberry pollen.
Pollen sourceYellow-green, 1 to 2 inches long, male flowers (catkins). See pictures below.
Tree leavesSerrated leaves can grow anywhere from 5 to 10 inches long. Mature leaves can form lobes.
Tree fruitIn dioecious trees, only female trees bear fruits, which is a fleshy drupe, similar to blackberries, but for some species, the fruit is longer.
Tree shapes and sizesSmall to medium-sized trees. Most city trees are 10 to 30 feet tall.
four mulberry catkins which are the source of allergy causing pollen. Two beady green on top are immature and the bottom two, which are yellow green are mature. The picture is taken next to a US quarter. The catkins are 1 to 2 inches long.
White mulberry male flowers (catkins). They produce and release pollen.
three green leaves on a black background. Each leave has sawtooth edges, one has three lobes, one has none, the middle one has a slight dent on one side but not a fully formed lobe.
Young early spring mulberry leaves: Notice the leaves are inconsistent in whether or not they have lobes. But, they all have sawtooth edges.

How to know if a mulberry tree is releasing pollen?

Only male mulberry trees release pollen. Unfortunately for the allergy sufferers, most city mulberry trees are males. The female trees are avoided because the fruit can clutter sidewalks and attracts birds.

The male trees start to bloom in winter. The green catkins appear before leaves and have a beady formation. As catkins mature and start releasing pollen in early spring, the tree canopy looks yellow-green.

Each tree releases pollen for four to six weeks each year. Eventually, the mature catkins fall off the trees.

A mulberry tree branch with about a dozen young, green, beady catkins that are about one inch long
Young male catkins of white mulberry. They are still about two weeks away from releasing pollen.
About 10 mature, yellow-green catkins of mulberry. The beady buds are open and the catkins are definitely releasing pollen.
White mulberry catkins, which are mature and releasing pollen.
A red mulberry tree foliage in early spring. There are no leaves, but the tree is loaded with pollen producing yellow-green male catkins.
A red mulberry tree in early spring bloom. The yellow-green foliage is entirely made up of male flowers and the tree still does not have leaves. [Morus rubra]

When do mulberry trees releases pollen?

Both white and red mulberry trees release pollen during March and April in the San Francisco Bay Area. The peak is generally hit towards the end of March.

Although mulberry trees are not as common as redwoods, cypress, and oaks, I still catch enough pollen in the Bay Area air surveys. This is because each tree is capable of producing billions of pollen. Furthermore, the mulberry pollen is much smaller than pollen of other trees. So, it stays afloat longer and travels farther with the wind.

If you are allergic to mulberry pollen, keep an eye on the trees in your neighborhood to observe their bloom during spring.

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

What does the mulberry pollen look like?

Mulberry pollen has two protruding pores, which makes them unique and easy to identify. The pollen is diporate, oval-shaped, and about 20 microns in size.

Under the microscope, the mulberry pollen stands out because it stains lightly compared to the pollen of other plants.

A small round pink pollen with one visible protruding pore. There is a hint of another pore on the other side , making it a total of two pores. The center mass seems granular.
White mulberry pollen (Morus alba)

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

What do mulberry trees look like?

The trees have larger leaves that can range from 3 to 10 inches long. The leaves are serrated and can develop lobes upon maturation. The trees are generally small to mid-sized.

Most city trees are 10 to 30 feet tall, but some trees could grow up to 60 feet.

A 20 feet tall tree with sparse yellow brown foliage, which is made up of male flowers. Leaves are absent.
A red mulberry tree in early spring before the leaves arrive. The tree only has male flowers. [Morus rubra]
Five to six, large serrated leaves with three lobes. The leaves are almost 8 inches long.
White mulberry leaves during fall [ Morus alba]
Grey brown scaly bark on a single straight trunk.
White mulberry bark and trunk [Morus alba]
A shiny yellow green leaf, surrounded by slender yellow and green male flowers.
A mulberry tree towards the end of its pollen cycle. New leaves are emerging and catkins are turning brown.

Key takeaway

Mulberry pollen allergies during spring are common in the US. The trees are found all across the US. The pollen is smaller than most of the other airborne pollen. As a result, it stays afloat longer and travels farther.

Considering the widespread presence of mulberry, all allergy testing facilities generally have mulberry pollen in their test panels.

The other trees that bloom alongside mulberry during spring are pine, oak, sycamore, cypress, birch, poplar, and sweetgum.

Sources

  1. https://plants.usda.gov/
  2. http://dendro.cnre.vt.edu/dendrology/factsheets.cfm

References

  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
  4. The trees of golden gate park and San Francisco by Elizabeth McClintock PhD.

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. The use of pictures is permitted with a link back to the source page on the internet, or, an attribution to allerma.com on the printed material.

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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