En Español

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

Need help with plant identification, visit the plant identification page.

rate this answer
1 rating

Tuesday - November 15, 2011

From: Austin, TX
Region: Southwest
Topic: Propagation, Seeds and Seeding, Trees
Title: Mexican Sycamore trees grown from seed
Answered by: Jimmy Mills


If someone is selling an alleged Mexican Sycamore grown from a seed harvested from a mature tree growing in Austin, is it likely to be a TRUE Mexican Sycamore -- or has it most likely been pollinated by an AMERICAN Sycamore, such that the resulting hybrid has an unpredictable mix of M. Sycamore and A. Sycamore traits? I have wondered because when almost every such tree I've seen for sale in Austin has leaf undersides which usually seem to lack the silvery sheen [or at least whitish cast] and/or the fuzzy underside that I've always assumed was the mark of a TRUE Mexican sycamore. How can I know if I'm getting "the real deal"? Are these trees simply hybrids at best -- and not true Mexican Sycamores?


You seem a little skeptical which is a good thing.

Lets learn a little more about Sycamores. The American Sycamore is Platanus occidentalis (American sycamore), and the Mexican Sycamore is Platanus mexicana.
P. occidentalis is native to the U.S., but P.mexicana is native to Mexico and therefore is not found in our NPIN Database. The Mexican sycamore has become popular in the last ten years as an introduced ornamental.

Sycamore trees are monoecious, having both pistillate (female) and staminate (male ) flowers on the same plant. However, it is doubtful that they are self-fertile,  ie. pollen from staminate flowers can not pollinate pistillate flowers on the same tree.  The trees are also wind pollinated. Since P. occidentalis and P. mexicana are closely related, it is not out of the question that they are able to cross pollinate and produce viable hybrids. So there is no way of knowing if the seed from which the tree being sold grew was the result of pollination from P. mexicana  or  from P. occidentalis. The odds of the tree being a hybrid seems pretty high unless the seed parent was growing in a grove of P. mexicana.

How can you tell the difference? One character that is easy to see is the the shape of the leaves. The link to austintreeexperts.com  says that P. occidentalis leaves are broader at the base, and will generally have an extra lobe that is lacking in P.mexicana. There are two photos on the link that show this distinction.

These two links from the Texas Forest Service have illustrations that also demonstrate this feature:

    Platanus occidentalis

    Platanus mexicana    mentions the silver underside of the leaf

Your best source of a TRUE Mexican Sycamore is to find one that was vegetatively propagated.


More Seeds and Seeding Questions

Source for Abutilon fruticosum (Indian mallow) seeds
September 24, 2011 - Do you know anyone who has Abutilon Fruticosum (Indian Mallow) seeds for sale? I would love to grow the Indian Mallow, but can't locate a source. Thanks!
view the full question and answer

Source for Texas Olive Tree from Tucson AZ
August 10, 2013 - Can one start a Texas Olive Tree from the olives it produces? How can you start one. I am having difficulty finding a nursery, but do see the trees around.
view the full question and answer

What to do about early seedlings
January 16, 2015 - Hello, Over the last few weeks I have noticed that all my naturally occurring poppies and delphiniums have started to sprout up around my yard. Hundreds of them! I imagine it's because of the ear...
view the full question and answer

How to grow bluebonnets in Atlanta TX
March 04, 2011 - How can I grow bluebonnets in Atlanta Texas?
view the full question and answer

Plants for steep embankment on the Missouri River in Nebraska
July 01, 2009 - Hi, My embankment along the Northeast Nebraska shoreline of the Missouri River is eroding the land away. Do you have any suggestions for seed I could throw over the side of the bank that would grow...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2016 Lady Bird Johnson Wildflower Center