26 July 2021

Two trees in the Birch family (Betulaceae) are common in the Pittsburgh area but I’ve struggled with what to call them because they have the same names.

Both are called Ironwood because their wood is hard, close-grained, and very strong. Ironwood is a poor name choice, though. About 160 species around the world are called “ironwood”.

Their scientific names are different but their default common names are very similar: American hornbeam (Carpinus caroliniana) and American hophornbeam (Ostrya virginiana). Hornbeam refers to their hard, strong wood: horn (hard, bony structure) + beam (Old English for tree). Hop is the only difference.

Fortunately they are easy to tell apart in the field at any time of year. In the photo at top:

• The bark of American hornbeam looks like sinewy muscles (top left).
• American hophornbeam bark peels in narrow parallel strips (top right).

Both trees produce fruit enclosed in an involucre, a whorl or rosette of bracts surrounding the inflorescence. This is where “hop” comes in.

• The fruit of American hornbeam looks like a drooping whirligig (left below).
• American hophornbeam fruit looks like hops, hence its name (right below). Click here to see what hops look like.

Both species with fruit and bark paired.

They differ by a hop.

p.s. Because of their similar names I sometimes call “hornbeam” by another common name: blue beech. More confusion!

(photos by Kate St. John)

13 July 2021

In Pittsburgh we hardly think about box elder (Acer negundo). It’s a native tree that grows by the river. No one plants it. It’s not a “bad” tree. So I was puzzled by this 1950’s story from my mother.

I never hear of box elder that I don’t think of your grandfather.  He never had a bad word to say about anyone.  He was a man of integrity and the absolute worst thing I ever heard him say was [this] about a member of the town council: “He was the kind of man who would plant box elder.”

— 1950’s family anecdote from my mother

My grandfather lived in a village in suburban Chicago in the heart of the Midwest where box elder is considered bad, ugly, weedy and invasive. Wikipedia provides this insight on how it got a bad reputation:

“After World War II, box elder’s rapid growth made it a popular landscaping tree in suburban housing developments despite its poor form, vulnerability to storm damage, and tendency to attract large numbers of box elder bugs. … It can quickly colonize both cultivated and uncultivated areas. … It grows around houses and in hedges, as well as on disturbed ground and vacant lots.”

In Wisconsin box elder is so disdained that the Urban Ecology Center wrote a blog in defense of it: Native Tree Spotlight: In Defense of Box Elder.

Box elder isn’t invasive in Pittsburgh so I had to go look for it on its home turf at Duck Hollow. There I found that as a shade tree it can look pretty good. This one is two box elder trunks intertwined.

However some of them die back leaving ugly bare branches at the top.

And if you cut box elder or chop it down it grows suckers from every crevice.

Midwesterners agree that box elder is bad. Why don’t Pittsburghers have this aversion? I think it’s because we are on the eastern edge of box elder’s range, we never planted it as a street tree, and it isn’t particularly invasive here.

What is invasive here? Japanese knotweed! Originally planted as an ornamental, we don’t think it’s pretty anymore.

If my grandfather had lived in Pittsburgh perhaps he would have said “He was the kind of man who would plant Japanese knotweed.”

Aha. Now I get it.

p.s. Later this summer box elder bugs will appear though not in huge numbers at Duck Hollow.

(photo at top by Tom DeGomez, University of Arizona, Bugwood.org, remaining photos by Kate St. John and John English)

21 June 2021

The air smells honey-sweet in Pittsburgh this month because the basswoods (lindens) are in bloom.

American basswood (Tilia americana) is a native tree in eastern North America with close relatives across the Northern Hemisphere. In Europe Tilia species are called linden trees. In the British Isles they are “lime trees” though not at all related to lime fruit. (Aha! Lindens are the “avenue of lime trees” in English novels.)

Basswoods grow naturally in the forest (left below) but are often used in landscaping. You can recognize them by their large size and distinctive teardrop shape (right below).

In June you can find them by smell, which is how I discovered the basswood at top in Schenley Park on 12 June.

Bees find them, too, so here’s a word to the wise. Never ever spray pesticide on linden (basswood) trees in bloom. A pesticide company did that in Oregon in June 2013 and killed 50,000 bees, the largest native bee kill on record.

p.s. Sometimes a linden tree drops “sap” on everything beneath it. But it isn’t sap. It’s excretion from an infestation of linden aphids (Eucallipterus tiliae) that are sucking the Tilia leaves. The Toronto Master Gardeners website explains what to do. Again, do not spray the tree while it’s in bloom!

(photos by Kate St. John, plus Vern Wilkins and Richard Webb via bugwood.org)

Yellow-bellied sapsuckers (Sphyrapicus varius) leave behind evidence of their visit when they pass through Pittsburgh on migration. In their search for food sapsuckers drill horizontal rows of holes on tree trunks and large branches, then lick the leaking sap and eat the insects attracted to it.

The trees cope as best they can with this unusual damage. Shagbark hickories (Carya ovata) grow puckered bark around the holes.

Tuliptrees (Liriodendron) display clean holes.

This spring for the first time I’ve noticed trees bleeding orange sap after sapsuckers visit.

My best guess is that these are sweet birch (Betula lenta), also called black birch or cherry birch. Nothing says their sap turns orange, but a few facts tip the species scales for me.

• New sweet birch leaves resemble cherry leaves. (I saw this yesterday)
• The bark of older trees is dark and looks like plates.
• Sap rises in sweet birch trees later and faster than it does in maples. (true)
• We tap sweet birch trees and collect the sap to make birch beer. (Why is birch beer red?)
• Deer don’t eat sweet birches so they’re more common now in Pennsylvania’s forests.

Have you seen any trees that bleed orange sap?

Do you happen to know if these are sweet birches?

(sapsucker photo by Steve Gosser, tree photos by Kate St. John)

UPDATE! Horticulturalist Sara Showers points out: “This looks like a phenomenon called “slime flux,” when leaking sap – a sugary food source! – is colonized by yeasts and other fungi. Here’s an article from Cornell about the phenomenon: https://blog.mycology.cornell.edu/2010/04/30/tree-slime-stump-flux-and-microbial-consortia/

Meanwhile I’m becoming more convinced that the tree species is sweet birch based on its leaves and bark and abundant sap. No, the sap is not orange.