A Gardening Journal

Castor Aralia, More Spiky than Ever

Six years ago, my castor aralia had just three stems. Now there are a dozen or so. They'll remain leafless until new foliage emerges in spring, so their freakish thorniness is in full reveal.

 

Kalopanax septimlobus var. maximowiczii 113017 base of trunks 640 

 

For me, even a single viciously thorny branch that is naked from November through April is one kind of heaven. True, such lengthy, needle-sharp protrusions are dangerous, and could inflict deep puncture wounds. Prevention of "herbivory"—being eaten by an herbivore—is their function on behalf of their stems.   

 

Kalopanax septimlobus var. maximowiczii 113017 stem base 640

 

Their visual appeal to horticulture-crazed humans is an unintended plus. As long as you stay safe, the spiny growth of Kalopanax septemlobus var. maximowiczii is unexpectedly engaging. Notice, above, that the thorns on the lower portion of an older, thicker stem are much paler than those at its tip, below. These latter were formed just this past spring and summer.

 

 Kalopanax septimlobus var. maximowiczii 113017 stem tip 640

 

That younger growth is more colorful than older growth is typical: think of the brilliantly colorful twigs of Winter Orange lindens or siberian dogwoods. When that growth also involves thorns (think red-winged rose!), youthful coloring can extend there as well.

 

The pattern of thorns, below, also tells the story of stems that have lengthened for several years. Look right above the tip of my index finger, at the ring of bark encirling the stem. This was the tip of the stem—the end of the growth cycle for that season—a few years ago.  

 

Kalopanax septimlobus var. maximowiczii 113017 first to second sections 640

 

Below, the portion of that stem that was formed by the time two more years had passed—and, so, two more bark rings had been formed. Thorns to the left of the ring were formed that second summer; those to the right were formed the third. Notice how much more deeply colored both generations of them are. The coloring seems to persist for two years, then pales to the tones in the picture of this stem's still-older portions, above.

 

Kalopanax septimlobus var. maximowiczii 113017 fourth to fifth section 640

 

Below, the very tip of this stem, which developed over the summer just past. The cone-shaped terminal bud protects new vegetative growth that will begin forming next spring. The bud also marks the spot that, by next fall, will have become the newest bark ring. 

 

Kalopanax septimlobus var. maximowiczii 113017 fifth current season section 640

 

This longitudinal series of bark rings isn't formed just section by section. They are formed chronologically, year by year: each ring marks the end of one season's growth and the beginning of the next. They are analogous, then, to the concentric growth rings that are visible when tree trunks are sliced open, in that each of those rings also marks the annual increase of (in this latter case) the diameter of the trunk, not its height.

 

Whatever their color, the protective, pointy projections that plants form are so striking, so diverse, that there are several terms for them, such as thorns, spines, prickles, and bristles. Plants form these "Herbivores Beware" structures from almost any part of their above-ground growth. And, yes, it seems a missed opportunity that, even though there are herbivores such as moles and chipmunks that tunnel underground in search of edible roots and tubers, there are no herbivore-deterring growths that emerge from the roots of plants hardy colder than zone 8. While there are subtropical and tropical plants with above-ground trunks that are fiercely spinose due to modified roots, to my knowledge there are no plants that are spinose subterraneously. 

 

The leaves of many forms of holly have painful projections extending from their rims. There are needle-sharp projections from the leaf veins of some plants in the bean-tree and potato families. Most of what would otherwise be the leaves of many forms of cacti and succulents are entirely converted to needles. Thistles are famous for the rings of painful projections formed by their modified leaves, known as bracts, that are immediately below the flowers. These enfold the buds, and then form outward-and-downward pointing ruffs around the bases of the open flowers that, presumably, discourage creatures hoping to access the blooms by climbing up from below.

 

All leaf-based projections are known as spines, but there's such a diversity of sharp-and-pointy growths on stems that there's a variety of names for them. Some are formed from the bark itself, and are analogous to the hairs that emerge from the skin of an animal. These are correctly known as prickles, and they are what roses produce. 

 

Other pointy growths are actually modified tips of stems, and are known as thorns. One reason the thorns of hardy orange are so dangerous, then, is not just because they are long and sharp. They are, literally, woody: rigid, thick, and strong. They can puncture deeply, even through difficult-to-penetrate surfaces such as calloused skin or thin-soled shoes. The thorns of Caspian locust aren't just long, bloodthirsty, and woody; they are branched

 

Which of these kinds of Herbivores Beware structures are produced by castor aralia stems? Prickles are the least likely because they can arise from almost any spot of the bark, so their array can be irregular. But look at the detail of the castor aralia stem below. The little brown cone in the center—the detail just above the bottom joint of my thumb—is a vegetative bud. It's flanked at the left (which is directly below the bud when the stem is viewed as it grows: upright) by a pair of projections.   

 

Kalopanax septimlobus var. maximowiczii 113017 bud flanking spines A 640

 

Below, another bud, also flanked the same way. My conclusion, then, is that these "spinosities" are not prickles but, rather, either spines or thorns. Like the buds they flank, they are also emerging from within the stem's deeper layers; otherwise, such a careful alignment with the buds wouldn't be likely.  

 

Kalopanax septimlobus var. maximowiczii 113017 bud flanking spines B 640

 

But are they spines or thorns? There's confusion even among scholarly sources. This source refers to them as both spines and thorns; this one as prickles. Whatever they are—and whatever they are called—these colorful projections can make a striking show from fall through spring, when any plant with a distinctive personality is most welcome.

 

 

Here's how fiercely interesting this Kalopanax septemlobus was five years ago, no matter that it had just three stems.

 

Here's how lush the tree is when in leaf. 

 

Here's a look at the remarkable flower clusters of a free-range Kalopanax. Alas, my castor aralia will never display them: maximizing the impact of the young stems' thorns requires regular radical pruning—cutting all the stems down to a foot every spring, say—that prevents any of them from maturing to florally-productive (but only sparingly-spined) adulthood. A flowering Kalopanax would also be as large as any shade tree. There's no room for one in my garden.

 

 
 
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