November is a good time of year to look for hackberry trees in Pittsburgh and examine their fallen fruit. By now the pulp has worn off the pits, but unlike wooden cherry pits hackberries’ are like white seashells with a microscopic lattice of opal inside.
Common hackberry pits: one whole, one opened (photo by Kate St. John)
Learn about these amazing structures in this vintage article.
Then go find a hackberry tree (and an electron microscope).
Hackberry bark and bare branches make it easy to identify the tree, even in winter. The bark has ridges and the ridges have growth lines.
Hackberry bark has ridges. The ridges have growth lines (photo by Kate St. John)
Up in the bare branches, hackberry trees sometimes have twig formations called witches brooms “produced by the effects of an eriophyid mite (Aceria celtis) and/or an associated powdery mildew producing fungus (Sphaerotheca phytoptophila)” — from bugwood.
Yellow leaves and bare trees, Schenley Park, 23 Nov 2020 (photo by Kate St. John)
24 November 2020
By now all the leaves have fallen in the Pittsburgh area. Or have they? There are still a few trees with bright yellow leaves in Schenley Park — Norway maples.
As their name implies Norway maples (Acer platanoides) were imported from Europe where their native range extends further north than Pittsburgh. Our short November days are the same length as those they experience in October back home. The sun will be up for 9 hours and 39 minutes today, 24 November, in western Pennsylvania. That’s the day length on 21 October in Oslo, Norway.
Right now our native trees are bare or retain just a few yellow leaves at the very top (tuliptrees) or dried brown leaves overall (oaks and beeches).
Because non-native plants are out of synch with our seasons late November is the best time of year to see them in the landscape.
The trees with leaves are aliens!
Fun fact: Pittsburgh’s latitude is very far south of Scandinavia. Did you know we are on the same latitude as Madrid, Spain?
Quiz: What North American city is nearly the same latitude as London, England? The answer is surprising.
Drift of fluffy seeds from London plane trees, 17 March 2019 (photo by Kate St. John)
28 March 2019
Last week I found fluffy drifts on the sidewalks in my neighborhood. They’re the airborne seeds of London plane trees (Platanus × acerifolia), planted in Pittsburgh in the late 1800s because they’re tolerant of air pollution.
Like their parents — oriental plane tree (Platanus orientalis) + American sycamore (Platanus occidentalis) — London plane trees retain their dangling seed balls over the winter.
The Shapes of Trees continues today with an Asian import.
Some Pittsburghers call this tree a sumac but it’s a case of mistaken identity. Sumacs are in the genus Rhus. This tree is an Ailanthus, specifically Ailanthus altissima. Its common names include Tree-of-Heaven as it is called in China, and “Tree From Hell” because it’s so invasive in North America.
Ailanthus has a unique shape in winter with sparse, thick, crooked branches in an open crown. They’re always reaching up.
The branches look crooked from a distance because the twigs are stout and blunt and the buds are large and alternate. Each bud changes the angle of the twig. A twig can be as fat as your finger.
Ailanthus altissima twig (photo by Kate St. John)
Ailanthus grows easily in waste places. David Sibley writes in his Guide to Trees,
Trees have been known to sprout from roots 150 feet away from the original trunk and grow over 12 feet in a year.
Frozen sap of red oak, 10 Feb 2019 (photo by Kate St. John)
The weather this month has been up and down like a yo-yo: A low of 6oF on February 2, highs in the 50s and 60s for six days, then a low of 14oF on February 9. During those warm days the sap started running in the trees. I wouldn’t have noticed except …
On February 10 during a walk in Schenley Park I found flash-frozen sap on the damaged trees. At top, a fallen red oak made a red-orange waterfall. Below, a small amount of sap in a fungi-encrusted tree dripped like orange ribbons.
Sap runs and freezes inside healthy trees, too. We just can’t see it.
Tuliptree in winter, Schenley Park (photo by Kate St. John)
The Shapes of Trees continues today with the tuliptree or yellow-poplar, Liriodendron tulipifera.
Tuliptrees are the tallest eastern hardwood, 70 to 190 feet tall at maturity. They’re characterized by straight branch-less trunks for most of their height because they jettison their lower branches as they grow. The crowns have arching branches and up-swept twigs(*). On mature trees some branches are bent or zigzag, but they are never as gnarly as black locusts.
The photos below show their typical shape as seen from the side and below. Notice that the trunk is straight and limbless.
Silhouettes of two black locusts in Schenley Park (photo by Kate St. John)
Now that the leaves have fallen we can see the skeletal shapes of trees. Did you know it’s possible to identify them by shape?
Seven years ago I wrote a series on identifying trees by their buds and bark but I didn’t mention shape except for this gnarly twisted tree, the black locust.
Black locusts (Robinia pseudoacacia) are easy to find in Pittsburgh because we’re within their native range and they grow well in disturbed soil. They’re often described as brittle and invasive but that’s because of what we did to them.
Locust borer larvae drill holes in the heartwood and weaken the tree. Before 1900 the bugs were in balance but that year the locust borer population exploded everywhere. Since then black locusts are usually infected and brittle so the trees rarely reach full size before they blow down.
But they do retain their distinctive shape. Here’s another example.
Gnarled black locust tree (photo by Kate St. John)
On Throw Back Thursday, learn more cool facts about black locusts and how to identify them in this vintage article: Winter Trees: Black Locust. Then take a walk outdoors to find their distinctive gnarly shapes.
In the next few months I’ll add more Shapes of Trees as I encounter them outdoors.
(photos by Kate St. John; map from Wikimedia Commons. click on the caption to see the original)
Hackberry fruits, pictured at top, are drupes similar to cherries and peaches with fleshy fruit surrounding a central pit. The fruit is thin and the pits are large so we rarely eat hackberries but birds love them.
The pits in cherries and peaches are made of wood (or something like it) but hackberry pits are made of stone: calcium carbonate inside a lattice framework. When Hope Jahren used Xray diffraction on the crushed lattice material its composition came up “opal.”
When I found this out I searched for the pits under hackberry trees in Schenley Park. At this time of year the fleshy purple fruit is gone, only the white pits remain. Here’s what I found, one whole, one opened. The exterior is a network of tiny raised lines.
Opal is in these hackberry pits (photo by Kate St. John)
The pits don’t look like opal and probably never will. You’d have to use acid to remove the calcium carbonate (which is the white stuff of seashells) and then examine the remaining latticework under a microscope. There’s a tiny bit of opal in there.
And so I wonder: How does a tree put opal in its drupes? I don’t know, but here are the raw materials:
Opal [rock] is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.
