Wednesday, May 8, 2019

Tree-following Stand-in: Singleleaf Ash (or is it?)

Obviously I’m not in Laramie, Wyoming, where it’s currently snowing. Instead, I’m 350 miles to the south and 3000 feet lower—in Fruita, Colorado. Unfortunately I forgot to visit the still-unknown tree that I'm following before I left home, but maybe that's just as well. I'm pretty sure it hasn't changed since last month's report.

Yesterday I considered various candidate stand-ins. Though this is dry country, there are many to choose from—maybe a tree in my friend’s yard or along the Colorado River path or in one of Kenton’s very cool native landscaping projects. But then I remembered the Singleleaf Ash and my mind grew dreamy. That would be my tree.
Fraxinus anomala, McInnis Canyons just south of Fruita, 2012.
“It had the distinctive one-winged fruits of ash trees! But could this be an ash? with only simple leaves instead of the compound ones typical of the genus?? and growing in the desert??? Yes! ... evolution has reduced the compound leaf to a single leaflet, hence the name. The scientific name suggests that the botanist who first described this tree was surprised as well: Fraxinis anomala.”
So wrote a fledgling blogger seven years ago (yikes!). I kept reading …
“Single-leaf ash, Fraxinis anomala, is a tree of the high-deserts of western North America. It grows from westernmost Colorado, where this photo was taken, west to easternmost California and south into northern Arizona and the northwest corner of New Mexico.” (1)
I knew the Singleleaf Ash grows in the dry canyon country just south of Fruita. But how easy would it be to find one? It's hardly common, requiring more water than most desert plants.
“… [some] ‘desert’ trees avoid arid conditions by growing where more water is available. Desert washes look dry much of the year, but often there is water fairly close to the surface, within root-reach. Tree cover often is greater in washes.”
When I hiked the Pollock Bench Trail in the McInnis Canyons National Conservation Area, I scanned each wash along the way. Soon I spotted my tree, plus a great perk for my field assistant.
While she frolicked in the muddy water, I again pondered the unusual leaves. In the absence of other evidence, it's really hard to believe this tree is an ash!
As I wrote seven years ago, most species of ash have compound leaves, meaning with multiple leaflets. The Green Ash leaf below, with seven leaflets, is typical.
Fraxinus pennsylvanica, courtesy TreeLib.
Fraxinus anomala is indeed an oddball among the ashes. Its undivided leaves are guaranteed to confuse a botanist unfamiliar with this tree. In my googling, I came across an essay by Craig Holdrege, a kindred spirit, who noted:
“To my amazement, I recognized the fruits as ones I knew as belonging to ash trees (the genus Fraxinus, Figure 2). Later I saw specimens with flowers that were also characteristically those of an ash. But ash trees always have divided leaves—so I thought—and the leaves of these shrubs clearly had simple round blades and long leaf stalks.”
Craig didn’t mention the problematic common name, which apparently didn’t bother me either seven years ago. But now I can’t ignore it. Why is this tree called Singleleaf Ash? After all, it has far more than a single leaf.

Maybe the answer seems obvious … it’s because most ash species have leaves with multiple leaflets, whereas Fraxinus anomala leaves have only one (2). But if you think about it, the common name doesn’t truly describe the situation. Though the leaves of Fraxinus anomala are sometimes described as simple (not compound), more likely they’re actually evolutionarily-reduced compound leaves, now with just one leaflet. Consider the California or Two-petal Ash (Fraxinus dipetala) below, thought to be a close relative of F. anomala (3). It’s easy to imagine a simple evolutionary step from multiple leaflets to just one.
Fraxinus dipetala; poto by Keir Morse (CC BY-NC-SA 3.0).

Therefore … [FANFARE!!!!] … Fraxinus anomala should be called the Singleleaflet Ash! Not impressed? Nor am I. This is just my mind entertaining itself. Let’s move on to something more interesting—the trees.

Three trees grew next to a shallow wash with low sandstone steps (above)—two on the left and one on the right. Does the second tree from the left look different? a bit more yellow? Yes … because it was covered in young samaras (seed pods).
I noticed that both the single leaflets and the samaras are shorter and broader than is typical for ash species (compare photos below). Is the same developmental thing going on? It’s fun to speculate, but for an answer, we’ll have to wait for the evo-devo folks to take an interest in ash trees.
Leaflets and samaras of the Green Ash (source).
Singleleaf Ash samaras from my 2012 visit to McInnis Canyons (different tree).


(1) I’ve since learned that the range of Fraxinus anomala extends into Mexico. It also has been reported for Wyoming, my home territory, but I could find no documentation online … something to investigate when I get back.

(2) Some individuals of Fraxinus anomala produce three or even five leaflets, but these are uncommon.

(3) Wallander, E. 2008. Systematics of Fraxinus (Oleaceae) and evolution of dioecy. Plant Systematics and Evolution 273:25-49.

For this month's tree-following news, and information about joining us, see May's gathering, kindly hosted by The Squirrelbastket.

Friday, April 12, 2019

News of My Old Tree Friend & Two New Ones

A lovely spring day in Laramie, Wyoming. 

Though spring has officially arrived, I knew I wouldn’t find any visible changes in the two trees I’m following. Here in the continental interior at 7200 feet elevation, it’s too early for flowers or leaves on trees. But there is one exception—the American pussy willow, Salix discolor. So before I checked on the trees by the art building, I walked up “Willow Canyon” just east of town to see how the willow was doing.

I discovered this willow on a hike in late February, 2015. Catkins were already emerging! Just the tips were visible, but still I was astonished, and chose the willow as the tree to follow that year. And of course it soon became “my willow” … trees are that way.
A full healthy canopy; August 2015.
I still visit my willow periodically. It's a beautiful tree when fully leafed out, but last August I discovered to my horror that all the leaves were dead! It was much too early for annual leaf fall, so I presume it was because of our drought. “What does this mean?!” I was worried

 … and I was really happy yesterday when I found it covered in catkins :-)
Willow standing behind two junipers.
Tiny white dots are catkins, not snow.
A few dead leaves still hang on ... imagine the canopy full of these!
Occasionally the sun broke through the clouds, making the catkins shine.
These catkins are not as far along as those of April 2015 (below). I'm not surprised. We're having a cool snowy spring. But snowy is fine—we need the moisture.
April 2015.
By the time we got back to the car, the snow had stopped and the sun was out, lifting my spirits even more. Off to the art building!

The late afternoon sun partially lit the two trees I'm following this year, highlighting their beautiful bark. As I suspected, I found no clues as to identity. The buds didn't help (do you recognize them?)
Next I visited the castle ... still no signs of residents. Maybe they're snug and warm inside, and haven't bothered to shovel the walkway.
The woman standing by the entrance last month was still there. And not even shivering!
Nor was I, but my hands were cold after taking photos (no gloves), so I went inside to enjoy the artwork. Student exhibitions change monthly, which is nice for a tree follower. I took photos of a piece I found especially appealing—something about the color and form.
Lattice by Donatellia Austin, 2018; Paper, Fabricated Steel.

I wondered if anyone would tell me not to photograph the artwork, but the few people who walked by said nothing, didn't even glance my way. Then I looked up and realized ... I was being watched!

For more tree-following news, see April's virtual gathering kindly hosted by The Squirrelbasket. And again, thanks to Lucy Corrander who started the whole wonderful business years ago.