The lowly hobblebush is a fascinating plant, for three main reasons, one of which makes it a "missing link."
I've always been interested in the natural world, but for most of my life, I paid far more attention to animals than to plants. I took the common view of natural history, which I have heard described as "animals moving against a green background." Only in recent years, I've begun to pay more attention to plants, and I've discovered a whole new world of fascination.
Take the hobblebush (Viburnum alnifolium), for instance. It's a rather common plant in the higher elevations of New Hampshire. It usually does not dominate the understory, but it is present nearly everywhere, especially where hardwoods dominate the forest canopy. It is a small, unimposing plant, and very easy to overlook.
But pay a little more attention, and you'll notice some rather extraordinary things about this ordinary plant.
Three things, in particular, have drawn my attention to the hobblebush: Its general growth habit, its leafing habit, and its flower structure.
Any one of these features would make the hobblebush rather interesting. Combining all of these features, the hobblebush is utterly fascinating. And I believe it truly might represent an evolutionary intermediate step between two unrelated groups of plants, a living "missing link."
First, there is its growth habit. Although it is called a "bush," it is not "bushy" at all. It is something between a tree and a creeper. But it isn't tall like a tree, and it doesn't lean on other plants or objects like a creeper.
Most typically, the hobblebush consists of a single trunk that rises ten to twenty inches off the forest floor, and two long, horizontal branches extending in opposite directions. These branches might be as much as six feet long, but they do not droop back to the forest floor, and they do not extend much above the height of the main trunk.
A fairly typical hobblebush with a long, horizontal branch extending to the right.
All of these structures - trunk and branches - are extremely thin and flexible, making their horizontal attitude all the more interesting. Why don't the branches sag under the weight of the enormous leaves? I don't know why, but they don't.
So, these long, horizontal branches just above the forest floor give the impression of a creeper, but close examination reveals that this plant is not a creeper. It does not touch the forest floor anywhere but where its main trunk emerges from its roots, and it does not lean on other plants for support.
It is this long, thin, horizontal growth habit that gives the hobblebush its common name. It's easy to trip over as you walk through the undergrowth.
(Incidentally, I've read some sources that say it got its name because Indians used to use it to make hobbles for their horses, but I very much doubt this. The Indians of the wooded mountains never had much of a horse culture, and they had such close cultural and economic ties to European colonists that they would certainly have used leather or twisted-fiber ropes for hobbles, as the colonists did, rather than improvise them from the hobblebush. Hobblebush is quite pliable, but better for baskets than for hobbles. Also, I've read some sources that say the long branches sometimes droop to the forest floor and take root, making the plant that much easier to trip over because it is rooted in two places. I have never seen this myself, and I have examined these plants very thoroughly and in many different places. Never seen it with two sets of roots.)
When it grows in a clearing or other sunny place, it assumes a decidedly tree-like habit. Its trunk can become a couple of inches thick, it can grow well over ten feet high, and it puts out short, sturdy branches in all directions. It loses its creeper-like tendencies, but it is still not bushy. It's a small tree.
In the normal course of things, the hobblebush combines characteristics of a tree and a creeper, but this is not why I call it a "missing link."
Another unusual characteristic of the hobblebush is its leafing habit.
Being a perennial deciduous plant of the understory, it is one of the first plants in the forest to put out its leaves in the spring. Nothing really unusual there.
Also typical of understory plants, it has rather large leaves to catch as much as possible of the sparse light filtering through the forest canopy. Again, that's not so unusual.
But the hobblebush does two unusual things to maximize its leafing season.
First, when summer is drawing to a close and its tattered old leaves have been gathering sunlight for nearly half the year, it loses these leaves and grows a second set of leaves.
Even as the old, tattered leaves of summer are turning burgundy and falling off,
a new set of green leaves is unfurling.
(Click the picture to see the full-size version, which is a little clearer.)
The large leaves of the hobblebush turn a deep burgundy toward the end of August, when the rest of the forest is still in the green height of summer. But even as it is putting on fall colors, the hobblebush is undergoing a second springtime of new buds. As its first leaves of the year are falling off, a new set of leaves unfurls.
Although they nearly always turn a deep burgundy,
sometimes the leaves of the hobblebush can turn scarlet.
Or even orange!
Note the bare corymb where the birds have taken all the berries.
Now, of course, evolution is just a process of the survival of the fittest, but it is difficult to avoid viewing living things as having been purposely designed. And this "design" is brilliant! Just as the forest canopy thins out and a new flood of late-season sunshine hits the forest floor, the hobblebush is ready with a fresh set of green leaves to take in more energy before the freezing weather sets in.
These second leaves of the year are much smaller than the first, but they get the job done. They have very little shade from the bare canopy trees, and virtually no competition from other understory plants.
When at last these second leaves have done their job, the humble hobblebush pulls off one more leafy surprise. As its autumn leaves finally wilt and fall (fading to yellow and brown, unlike the striking burgundy of the summer leaves), the plant puts out yet another set of leaf buds!
The hobblebush bears nearly-open leaf buds right through the winter.
These buds will remain on the plant throughout the winter. They begin to open, showing the shape and the vein structure of the leaf-to-be, but they do not extend more than about half an inch, maybe an inch at most. And there they remain, incongruously delicate-looking half-open leaf buds in the biting cold and shattering ice of winter.
Few creatures eat the leaves or buds of the hobblebush. I suppose they are slightly poisonous or otherwise indigestible. However, the moose will browse on them in winter when there is little else to eat, giving the hobblebush another of its common names: moose bush.
Yes, the leafing habit and annual cycle of the hobblebush is extraordinary, but this is not why I call it a "missing link."
The most unusual, possibly unique, characteristic of the hobblebush is the structure of its flower clusters. At first glance, it looks like any other flat disc-shaped flower cluster (a corymb, for the technically and botanically inclined), but a closer look reveals features that remind me of the flower structure of the daisy family.
What we commonly view as the "flower" of a sunflower or aster or daisy (members of the family Asteraceae distinguished by this highly specialized flower structure) is actually a very dense cluster of dozens, or even hundreds, of tiny florets. Each floret is a complete flower with its own stigma and anthers, though most of them have no noticeable petals. What we perceive as the "petals" are actually separate florets, each with one enormous petal.
The typical Asteraceae flower head consists of two general types of flowers. Those in the interior of the disc are called disc flowers, and they have petals that are fused into a tiny tube (along with the sepals). Those around the edges of the disc are called ray flowers, and they each have one petal that "radiates" from the edges of the flower disc, and they are usually a different color from the disc flowers.
A typical Asteraceae, the oxeye daisy (Chrysanthemum leucanthemum),
has a flower head consisting of dozens or even hundreds of tiny florets.
The white "petals" are actually separate florets.
Incidentally, the orange hawkweed (Hieracium aurantiacum)
in the background is also in the family Asteraceae, but its
atypical flower heads consist entirely of ray florets.
There are exceptions within the Asteraceae family. Dandelions, for instance, have only ray florets, even in the interior of the flower disc, and they are all the same color. Chamomile has only disc florets and no ray florets at all. But the typical Asteraceae flower has distinct disc and ray florets.
And the distinguishing characteristics are that the ray florets are of a different structure (having a large petal) than the disc florets (virtually lacking petals), and that the ray florets are much, much larger than the disc florets.
So, what about the hobblebush? Its flower cluster is clearly an open cluster and not a dense flower head like the Asteraceae flower. Each individual flower is on a clearly separate stalk rather than packed into the typical Asteraceae flower head. However, the flower cluster of the hobblebush (and some other members of the genus Viburnum) is unusual, perhaps unique, in that the flowers around the edge of the cluster are much, much larger than those in the interior of the cluster.
Close-up of a hobblebush flower cluster. There are usually more "peripheral" flowers than this,
but this picture shows the two different types of flowers very clearly.
Take a close look at the flowers of the hobblebush. The flowers around the edges of the cluster are dramatically different from those in the interior. All the flowers have five petals, but the "perimeter" flowers are enormous by comparison. The "perimeter" flowers have a peculiar ridge within each petal, almost creating a double-petal effect. The "perimeter" flowers have no stamens, but each does have what appears to be stigma identical to the stigma of the interior flowers. (I've read that these "perimeter" flowers are infertile, so this knob might not actually be a stigma, or it may be nonfunctional.)
A hobblebush in fruit shows the structure of the corymb clearly.
A closer view of hobblebush berries.
This suggests to me that perhaps the flower of the hobblebush represents something of an evolutionary transition from the clustered flowers to the specialized flower heads of the Asteraceae family.
I've never read this before, and I could be entirely wrong, but I think this bears further scientific investigation. There are worlds of questions to be asked, and I don't have the time or resources to explore them. Are there other plants that exhibit this size difference between the interior and perimeter flowers of the cluster? Could genetic analysis reveal any relationship between the hobblebush (or plants with similar flowers) and the Asteraceae family? Once the plant begins to blossom, if the perimeter flowers are destroyed, would the interior flowers now on the edge of the cluster assume the size of the original perimeter flowers, or would they remain small as interior flowers?
By the way, the fact that the hobblebush is a woody perennial plant does not necessarily indicate that it is unrelated to the Asteraceae family. Most of what we think of as typical Asteraceae are annual plants, but some of them are perennials and some have woody structures above ground. The only woody Asteraceae with which I am familiar is the brittlebush (Encelia farinosa), but I'm sure there are others.
Consider the fascinating things I have observed about the seemingly ordinary hobblebush. How many other mysteries are out there, waiting for you simply to notice?
Get out there and notice!