Plant Revenge -- or is it?

So-called “fragile” prickly pear (Opuntia fragilis) takes revenge on an unsuspecting botanist.

As part of my work, I routinely dig up plants and press them flat.  So sometimes when I’m struggling to remove plant parts from my hair, clothing and skin, the thought crosses my mind -- “this is revenge!”

Getting scotch thistle (Onopordum acanthium) into a plant press requires caution and the right tools: brick hammer to dig up plant, knife to slice heads into pieces.  Click image for view of dangerous plant parts.

Plants have lots of vexing and painful parts -- spines, thorns, barbs, prickles, glochids, retrorse hairs and dangerously-sharp leaf tips.  As biologists we assume these are adaptations, but for what?  It’s tempting to think defense.

The leaf tips of Agave lechuguilla, shin dagger, can be deadly.  From USDA Plants.

Retrorse barbs of wild licorice (Glycyrrhiza lepidota) look nasty ...

... but they're only a few mm long, as seen here in context (dog fur).

Retrorse spines and barbs make plant parts difficult and painful to remove, but their purpose could be considered noble -- to send offspring out into the world.  Wild licorice is very effective at dispersing seed this way, as my dog frequently demonstrates (see Leaving Home).  [retrorse: (Botany) (esp of plant parts) pointing backwards or in a direction opposite to normal]

Puncturevine nutlets are especially devilish (Tribulus terrestris; source).

The fruits of puncturevine also have barbs, but they're so hideous that I have to think their purpose is evil.  The plants grow low to the ground, often over large areas.  When the fruits dry, they split into hard nutlets with nasty sharp little spikes that are very good at attaching to feet and tires.  They puncture the feet of whatever passes through the patch; walking then becomes extremely painful.  Removing nutlets with ones mouth (what else can most animals do?) makes the situation even worse, and can cause death.  This seems over the top.  Do these structures really aid in dispersal if they cause us to avoid the plants?  So perhaps they’re weapons “for” defense -- but do they increase chances of survival given that we kill the horrid plants wherever we find them?

Puncture vine mat and closeup of flower.  Flowers are 0.5-1 cm across.  Source.

The most infamous pain-inflicting plants in North America are cacti, with their diverse assortment of spines.  Surely they are adaptations to discourage animals from eating the delectable fleshy stems, so appealing in deserts.  This is a reasonable conclusion.

Prickly pear cacti have tiny very sharp spines called glochids below the regular spines.  They're especially difficult to remove from skin.  Some cultivars are spine-free -- these are the tasty nopales or indian figs.

However there seem to be other “purposes” for cactus spines as well as defense. Consider that they’re found mainly in deserts -- plants of moister regions are rarely covered with spines.  Might spines shade stems and reduce water loss?  For the fragile prickly pear (beginning of post) and the infamous jumping cholla of Arizona (below), they appear to be "for" dispersal.  Stem segments readily disarticulate, and can attach to an unsuspecting passerby thanks to the spines.

Though many purposes can be conjured up by a curious partially-informed mind, it’s difficult to know why a plant structure evolved -- what it’s an adaptation for.  We rarely understand the evolutionary history of adaptive traits.  For example, something may have evolved for an unknown purpose long ago, and later was co-opted or redesigned for something else.  The opportunities for speculation are infinite.  There’s a thought-provoking discussion about this dilemma at The Mermaid’s Tale:  Why do cholla cacti use torture?, written by Anne Buchanan after a hike in the Arizona desert.

“The problem is that there may be no single reason, nor even any single kind of history involved here.  ... we think this illustrates why, even when the assumption that the trait is 'adaptive'--that is, is here ultimately because of natural selection--that assumption is hard to prove and in particular the reason is hard to be sure about.”

[Warning:  the included video featuring an unfortunate victim of cholla torture is not for the squeamish.]

Jumping cholla, Cylindropuntia fulgida.  Source.

Obviously we need to be cautious, not just in walking through dangerous plants but also in thinking about them.  Like so many biological phenomena, the more we learn, the more complicated it gets [sigh] but of course that makes the stories even more wonderful!  Here’s a great example:

Bullhorn acacia, Acacia hindsii.

The bullhorn acacia is a well-armed desert tree, with long spines that deter browsers in ways both obvious and surprising.  Obviously the sharp-tipped spines discourage larger animals, but they don’t do much against insect pests and fungal pathogens.  Fortunately they also serve as ant homes, and in fact, the acacias strive to make the neighborhood attractive to ants by providing nutritious food via extrafloral nectaries.  It’s worth the investment.  The ants sting anything that tries to eat the leaves, from caterpillars to cattle.  Furthermore, acacias with healthy populations of the right kind of ant have a reliable supply of antibiotics to fight fungal infections on their leaves.  Their drugs are produced by bacteria living on the ants’ legs.  What a nice arrangement!  For more, see The Economist, Protect and Survive; and Science Daily, Ants protect acacia plants.

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This post is my submission to this month’s Berry Go Round, a blog carnival for plant lovers.  It’s hosted by Garry Rogers, and the topic is Botanical Warfare.

Spines are for beauty too -- for those who look close (from Excruciatingly Beautiful).

Some days there's beauty everywhere

Cattails on right, dogtail on left.

Why did I take photos this morning?  Because I could.  There was no wind beyond a slight breeze, and it was possible to photograph inanimate objects and even plants.  It was wonderful, it was exhilarating, it was paradise -- compared with the previous five days when it was impossible even to stand still.

Here in Laramie we are a resolute people, as Garrison Keillor might say.  We know there are many advantages to living here (but we don’t tell what they are as we want our town to remain small and friendly).  We know they far outweigh the disadvantages, which we stoically endure.  But there are days.  There are days for example when it's dangerous to get out of the car if it's parked into the wind.  My parking spot at home points west, and yesterday it was all I could do to open the car door and get my groceries out and not be crushed as it slammed shut.  The average wind speed at that time was 45 mph.

So you can imagine my joy when I awoke this morning at a normal hour, instead of at 3 am due to the roar of wind (wind roars when its steady speed is greater than about 35 mph).  You can understand why I did not mind that the day was gray with a light snow falling, and can sympathize with my decision to forego laundry for a photo excursion.  But of course I’m making assumptions.  If you’re a person who disapproves of impetuous behavior, then read no further.

I abandoned the laundry and went for a walk.  I kept my camera on the entire time and photographed whatever I found, for it all seemed beautiful to me.

The sun shone dimly through thin clouds and light snow.

We crossed the shortgrass prairie - light industrial ecotone on the west edge of town ...

Tumbleweed hanging out with railroad tie (prickly Russian thistle, Salsola tragus).

... and reached the Laramie River.

This is the tree I'm following, a cottonwood.

Another tumbleweed taking the day off, resting on river ice (kochiaweed, Kochia scoparia).  

Cattail still-life (Typha latifolia).

This one is waiting for the wind to return, so it can send more offspring out into the world.

Just west of the wetland is Interstate 80, one of the main arteries of the USA.  Crossing the Laramie Basin isn't so bad, but the mountain passes on either side can be terrifying in winter.  But we need our stuff!

Rich's bench ...

... and Rich's Four Noble Truths (click on image for a better view).

By the time we returned to home and laundry, the sun was out but the wind was back. Clearly we had made the right choice in seizing the day.

Getting to Know a New Friend(s?)

Lucy of Loose and Leafy has stepped up her efforts to organize and encourage tree-followers.  This is very kind, as tree-following is always interesting and it's fun to share discoveries.  We choose a tree to follow through the year, and there's so much to learn.  What kind is it and how do we know?  When do leaves appear? flowers, fruit?  Who lives there?  How does it catch the sunrise?  Does it do justice to the golden hour just before sunset?  These are all important things, and it’s our responsibility to find out.

Stirred by Lucy’s enthusiasm, I took my camera with me on my morning walk along the Laramie River.  It’s still winter here, so I got side-tracked by the beauty of river ice.

Center foreground -- our tracks from last week, now inverted because most of the snow has blown away.

Footbridge across the river, once a railroad bridge.

Shadow patterns cast by grass, brush and trees.

My field companion, as faithful to me as his shadow is to him.

I returned to my mission and soon chose a tree for 2014 (below left).  Or maybe I should say “trees” as there are multiple trunks.  Most of the trees along the river grow this way, in clumps.  Is this a single individual, connected underground?

Winter landscapes can seem so dreary.  But if we can get out of that black-and-white mode caused by snow, we realize there's quite a bit of color after all.

Another view -- the tree stands over its cousins, the willows.

Its twigs appear bare at first glance.  A closer look (click on image) reveals buds ready for spring.

Trees often are challenging to identify without leaves, but I gave it a shot.  I ran a dead leaf through the Rocky Mountain Tree Finder, partly because I love dichotomous keys and this one is so easy to use.  How does it work?  At each step I pick one of two choices, thereby eliminating a substantial number of tree species from consideration.  I continue this way until the only one left is the one I’m standing under!  It seems like magic, even after all these years.

In this case, the path to identification required 14 steps, including the following:

1) Leaves needle or scale-like OR ordinary?  ordinary

2) Leaves compound, composed of several leaflets OR simple?  simple

3) Leaves paired on opposite sides of twigs OR not?  not (no leaves, so checked leaf scars)

4) Leaves lobed OR not?  not

5) Leaf stalks (petioles) longer than 1 inch OR less than?  less than

... etc. ...

10) Leaf margin with big & little teeth OR single-sized teeth?  single-sized

Leaf margin with single-sized teeth.

and finally:

14) Leaf tips often blunt rather than sharply pointed OR not?  often blunt rather than sharply pointed (see illustrations below)

It appears to be the narrowleaf cottonwood, Populus angustifolia (click on image for more information).

I also attempted to identify the tree with the Winter Tree Finder.  This is challenging because the useful characters are harder to see and not as familiar.  I had to look at terminal buds, leaf scars and vein scars -- so let’s digress.

From the Winter Tree Finder.

The terminal bud is where the twig will start the year's growth.  Leaf scars are left when leaves fall off.  They contain vein scars -- remnants of conduits (phloem, xylem) for transporting water, nutrients, carbohydrates and more.

Now back to identification.  I went straight to the cottonwood section.  The Winter Tree Finder says terminal buds of cottonwoods are symmetrical.  According to the Audubon Society's Field Guide to North American Trees, Western Region, terminal buds of the narrowleaf cottonwood are resinous and smell of balsam.  Let’s look:

The terminal bud is indeed symmetrical, and somewhat resinous too.  I didn't detect a balsam odor.

The Winter Tree Finder says leaf scars of cottonwoods are crescent-shaped with three vein scars.  Sure enough, there are three vein scars on each crescent-shaped leaf scar:

The leaf scar below the bud is from last year; the one near the base of the twig is probably two years old.

The terminal buds, leaf scars, and vein scars of my tree all match those of cottonwoods.  But I couldn’t go any further in the Winter Tree Finder because it covers the eastern USA, and Wyoming is in the west.

I'm sure this is a cottonwood and probably a narrowleaf cottonwood.  The bark looks right:  “smooth, becoming gray-brown and furrowed into flat ridges at the base” (Audubon Society Field Guide to North American Trees, Western Region).  It's growing in the right kind of habitat -- lowlands or near water -- and well within its range (see previous map).

I will check my tentative identification after the tree leafs out, but first it will bloom and I'll need to investigate that as well.  Cottonwoods have unisexual flowers, either male or female, and the sexes are on separate trees (dioecious).  Thus I’ll learn whether this clump is male or female -- or maybe both, suggesting these are separate trees after all.

Cottonwoods along the Laramie River, in winter morning sun.

However I shouldn't dwell on tree activity right now.  It's only February.  Cottonwood flowers and leaves won't appear for months yet, probably in May, at least that's what I think I remember.  I don't always notice -- but this year I will.

Are you following a tree?  Sign up here or here to join the fun.

Your African Fold -- sojourn in the Namib Desert

Quiver tree on Cambrian/Precambrian dolomite overlooking dunes of the Namib Sand Sea.

Guest post by astronomer, geologist, poet and good friend Danny Rosen.

From 2003 - 2008, for a few months a year, I ran an observatory and taught astronomy and geology in the Namib Desert in far southwestern Africa.  I wrote this poem during a period of observing the best sky I’d ever seen every night for three months. There was essentially no light pollution. The Southern Cross, Alpha Centauri and the southern Milky Way were enough, but going deeper into the sky with a fine telescope was life changing. The poem sprouted when I began sleeping under the telescope to more easily wake for pre-sunrise viewing. I got caught up in the rising and lowering of the horizons, the planetary spin, and at some point imagined the eye of a Nautilus at the center of its spiral looking out -- like the human eye in the Milky Way.

As astronomer in residence I stayed up later than anyone and walked back to my room alone. There were animals about, and endless stories of rough encounters, some nearby, not all were just legend. I heard footsteps all the time and set folding chairs around my head to keep curious hyenas away. Lured by CO2, they are known to take investigative face bites of unwary campers.

The center of our galaxy is in the direction of the constellation Sagittarius. It’s dense that way: fields of stars, clusters of stars (butterfly, coathanger, jewell box), nebula seen with the naked eye, and the big and small Magellanic Clouds, spinning around. From Namibian latitudes this area of the sky is especially bright -- seen almost straight overhead, where we look through the least of our atmosphere, the stars are most clear. (We can see Sagittarius from mid-northern latitudes but it never gets very high above the southern horizon -- so, we look through a thicker slice of the atmosphere and the view is not as sharp.) That’s a good reason in itself to travel south.

Paul Theroux, in Dark Star Safari, wrote that V. S. Naipaul helped him see the comedy of Africa. Tragedy is more obvious with all the difficulties of the post-colonial period, and ever burgeoning and needy populations. People die young, life goes on, there is laughter and song, silly things are done, vehicles get stuck in the sand, there are difficulties with the hi-lift jack ...

It’s a hard rock desert canyon landscape inhabited by people whose ancestors go way back, overlain with a European cultural fabric, and a vestige of Pleistocene megafauna. Rhino on the desert floor. Continental knife and fork at the German Club. Eco-lodges with camouflaged diesel generators.

Des with Bev

Your African Fold

The sunrise in your gray eyes speaks

the history of man with no words.

Silence spirals across the sky.

This nautiloid look from the inside.

Wrapped in saugins and duvet,

with eyes wide against the sounds

outside, trembling at your footsteps

in the dawn moonlight, Sossusvlei,

I miss your naked eye nebula,

your pale chanting evenings,

the truth of your false cross.

I still see the baboons staring

down the gravel highway I drove

all the way to fata morgana herself,

her moist finger motioning me to jump

from the cliffs of my unspoken east.

I can still hear the what-what of your

quick click chit chat this that and the other,

tell me another story so hard from the start,

far from home, close to the heart. The tragedy

of the easy tip, the comedy of the kitchen lip,

the opera of the landy stuck in the sandy

and old jack hi-boy only knows one way to go.

Pull the damned thing out, sounds

Mr. Basso Profundo, ‘un-air these tires man,

get thee out of this godforsaken land.

’Godforsaken? Why,

here He comes just now, walking

through the shadow of a quiver tree,

out across the gravel plain, walking on one leg

with one arm and one eye that can still find

the road ahead. Namib lands,

I’ll sail through your lagoons anytime,

and paint butterflies in your sand all night.

I’ll lay by your side as you die before your time,

and see you rise again with Mimosa. Mimosa,

I can still feel the bowl of your soft dark belly

hanging above me every night, tucking me in,

rolling me over and over until I’d been rolled

into the arms of your African fold.

☆☆☆☆☆

Sossusvlei is an area of the central Namib Desert. The name derives from the Nama word "Sossus" -- no return or dead-end -- and the Afrikaans word "Vlei" -- marsh (similar to a playa lake). Gervasius Nangolo, a handyman, was a good friend -- he had gray eyes. Pale chanting goshawks are a common bird of the Namib. The False Cross is an asterism made of stars in the constellations Vela and Carina (part of the mythological ship Argo Navis that Jason sailed on his quest for the golden fleece). Many native people of the Namib, and throughout southern Africa, incorporate clicks into their language. Quick, loud, sharp clicks. Talk radio is great! (here's a cool instructional video).

Quiver trees (Aloe dichotoma) almost resemble Joshua Trees but have a more surreal nature. Gravel plains are the desiccated remains of horizontal rock layers that have broken down in place and been transported very little. They are emblematic of how geologically stable the area has been since Gondwanaland broke up and Africa split away from South America 130 million years ago. The “Lagoon” is a nebula in Sagittarius. The “Butterfly” is a star cluster in Scorpius. A “lay-by” is a roadside rest with a picnic table. I spent part of every night with Mimosa -- a star in the Southern Cross. For some reason, I thought the word "saugins" was a kind of blanket or comforter, but when I later looked it up, I couldn’t find it at all. Apparently, I made it up, but kind of liked the sound of it anyway and decided to keep it.

The quiver tree (Aloe dichotoma).

Euphorbia virosa -- the poison tree, 

Fairy circles below the Virgin's Nipple. Various explanations for the barren, sandy or gravelly circles in the midst of grassy plains have been proposed over the years, including ants, termites, and grass-killing gas emanating from the soil. A recent hypothesis suggests they're caused simply by plant competition for water and minerals. As University of Wyoming's Doc Mears might have said, probably all these possibilities are true in part.

Hartmann's Mountain Zebra, commonly seen on the Namib grasslands.

Gemsbok (Oryx gazella) on thick grassland (the area averages less than one inch of precipitation per year).  "Oryx" are a signature species of the Namib.

Dan Rosen lives outside Fruita, Colorado, where he runs the Western Sky Planetarium and Lithic Press, a free independent press devoted to making fine books for an old planet.