Thorns and Roses

Something is odd about the thorns on roses. I noticed it when I was trimming the plants in the yard. To get at the inner twigs, I reached in and down, avoiding most of the barbs, snipped away, and began to withdraw my hand. Yow! The little meat-hooks, pointing down along the stems at various angles, grabbed hold of any bit of glove, shirt or skin that grazed them on the way up and out. I thought of those “Don’t Back Up” signs at entrances to parking lots guarded by spiked grates that lay flat when you drive forward but are otherwise aimed upwards towards any tire coming out.

Thorns of the rose
(Flickr)

The most common explanation for thorns is that they discourage plant-eating creatures from nibbling. Are rose thorns in particular any less efficient at this because of their angle down the stem, instead of straight out, like, say, cactus spines? It’s difficult to say. True, on an untrimmed, mature rose bush with stems growing in every direction, the thorns seem to deter a hand or animal mouth moving in any direction. Moreover, an animal poking its snout in for a nibble may get snagged as it withdraws and then intensify that pain dramatically as it struggles harder to pull back and escape.

But maybe these slightly backward thorns serve other purposes beside deterrence. The Wikipedia entry under “Rose” cites a different advantage up front: “Rose prickles [“Prickles” are the proper name for such thorns that grow from the skin of a stem; true “thorns” and “spines” are  sharp, modified leaves or stems sprouting from the woody core]…Rose prickles are typically sickle-shaped hooks, which aid the rose in hanging onto other vegetation when growing over it.” “Sickle-shaped hooks!” And “grappling hooks” as well.

A third factor in the rose thorn question is whether thorns and spines successfully deter caterpillars from climbing up to eat leaves and flowers. It seems that they do; at least, they slow them down, according to Christie Wilcox’ reporting on the work of entomologist Rupesh R. Kariyat in Zurich (“The Thorny Truth About Spine Evolution,” Quanta magazine June 14, 2017).  The current evidence suggests that while the first thorns and spikes “evolved against mammalian herbivores” a couple of hundred million years ago, many plants’ tissues gradually became toxic and repelled animals, while thorns stuck around (not intended) as the most effective defense against caterpillars.

Scientists agree that they have more to learn about thorns, spines, and prickles than they thought. Wilcox concludes that such under-research “illustrates our own species’ limitation and preconceptions. ‘When we go in the garden, we get cut by roses, so we perceive those thorns to be a defense against mammals,’ [British scientist Mick] Hanley said. ‘In almost every manifestation of understanding biology, we’re always putting our own human view on it.’”

Such biases may hold especially true for thorns and roses thanks to truisms about the pain that is said to accompany the search for beauty or love. The function of needle-sharp thorns in particular seems self-evident and unchanging. But the truer wisdom is that the capacities of hunters and hunted, seeker and sought, steadily evolve.

My Million-Year-Old Back Yard

I like knowing the age of living things—not the age of the individual organism but of the lineage, of how long a plant or animal has been different from other lineages. The dates give me a glimpse of a Past that, like a god, generates and then consumes everything.

So here are the ages, youngest first, of the plants and animals in my suburban yard. Dates are approximate by millions or tens of millions of years!

The youngest creature in the yard is our dog, an animal that separated from its wolf-like ancestors about 40,000 years ago.

Next is me and my wife. Our species, Homo sapiens, separated from our Homo ancestors about 200,000 years ago. Before that, our genus, Homo, split off from the genus that chimps belong to about 7 million years ago. All our ancestors in our genus have died off and we are the only member left, a strange isolation. We are probably the only species in the yard in that situation.

The youngest plant is the grass, appearing about 40 million years ago among plants that adapted to a warming climate.

Back yardThe first squirrel fossil dates from 36 mya. Squirrels are part of a huge group of rodents with big, continually growing teeth. The chipmunks are in the same category.

An oak tree dominates the yard. Although trees in general have been around for much longer, the oak was part of the spread of flowering plants, at very roughly 70 million years.

There’s a holly tree. The several hundred species of holly emerged about 80 million years ago.

Other flowering plants and trees come next. Their ancestors began diverging from flowerless plants around 240 mya, they were blooming 160 mya, and they became widespread and then dominant among plants during the 100 million years after that.

Insects originated about 600 million years ago, but the modern insects in the yard—flies, butterflies, wasps, bees, ants— co-evolved along with the flowering plants from 146 to 66 mya.

The birds are thought to have evolved from certain dinosaurs that carried feathers for warmth, about 180 million years ago.

The pine trees and cedars around the house are among the conifers that date back 300 million years when early trees began to live away from the water. Conifers reproduce through exposed seeds (on pine cones) and pollen. Protected seeds, enclosed in nuts and fruits, came later.

Two other back-yard inhabitants go back as far as the conifers: Ferns, not so different 350 million years ago, with their tiny, single-cell spores, another predecessor of the modern seed. And spiders, spinning their silk about 300 million years ago.

I’m realizing, as I finish hunting through Wikipedia for these dates, that my intentions have become a little muddled. The “birth” of these species was more process than event, a long interweaving with their early kin. The age of a rose depends on whether you look at it as a rose or a seed-bearing plant or a land plant.

Still, I savor the majestic history here, the story of life.