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HUMMINGBIRD MORNINGS
In 2004, informative and entertaining hummingbird banding presentations are scheduled for Aug-Sep in North Carolina, Ohio, Virginia & Kentucky/Tennessee.
Next Up: Canton, Ohio on 4 September
(Click on the logo at left for details.)
If your group would like to host Hummingbird Mornings anywhere in the U.S. or Canada in 2004 or later, contact
Bill Hilton Jr.

A DIFFERENT MIMOSA,
AND OH, SO SENSITIVE!

Across the Carolina Piedmont, hordes of plants from the Orient have found the region's red clay, ample rain, and mild winters very much to their liking. Our least favorite Asian import is the infamous Kudzu, Pueraria lobata, a fast-growing, tree-smothering vine we're grateful to have none of at Hilton Pond Center. (Knock on wood.) Instead we have Japanese Honeysuckle, Lonicera japonica, a twiny, viny plant against which--thanks to a sharp set of lopping shears--we seem to be holding our own. Overbearing Russian Olive, Eleagnus angustifolia, and prolific Japanese Privet, Ligustrum japonica, are pernicious shrubs we'll probably never be rid of, even though we use chainsaws and dynamite to deter them. (We exaggerate, but sometimes we ARE tempted to try incendiary devices--even though we doubt anything less than a nuclear warhead would have an impact on Chinese Wisteria, Wisteria sinensis.)

Despite the local success of these Far Eastern interlopers, the one foreign invasive we'd actually LIKE to have but can't seem to encourage at the Center is Mimosa, Albizia julibrissin (above left). This pink-flowered sweet-smelling tree--when kept in check--can be a real magnet for hummingbirds, native bees, and butterflies, but for some reason has not survived on our Hilton Pond acreage. In its absence we actually have another much-smaller Mimosa--Mimosa microphylla, the Little-leaf Sensitive Brier--a plant whose flowers are delightful to behold but whose real claim to fame is its behavior. "Plant BEHAVIOR?" you ask. Yes, plant behavior.

All text, photos & movies © Hilton Pond Center

Unlike the Mimosa tree--which originally occurred from Iran to Japan and now is found across temperate North America--M. microphylla grows naturally in the southeastern U.S. as far west as Texas; it is considered "very rare" and subject to possible extirpation in Virginia. And while Asian Mimosa is a woody tree that reaches 40 feet in height, its smaller local namesake is a perennial herbaceous vine whose green stems wind along the ground or ramble over low walls and shrubs. The 3-to-6-foot stems grow from a taproot that allows Little-leaf Sensitive Brier to overwinter underground and get a head start when warm days of spring arrive. We found our first plant at Hilton Pond Center back in the mid-1980s in a spot that is now too-shaded by new-growth trees; the specimen depicted on this page is in full sun on the Center's road frontage--right where road crews are likely to whack it back next time they cut vegetation along the shoulder. One vine from the taproot grows flat along the substrate, while the other has managed to find vertical support from low branches of an Eastern Red Cedar, Juniperus virginiana (large bottom photo).

The pink "powderpuff" blossom of Little-leaf Sensitive Brier is reminiscent of that of Mimosa trees, but to our eye it has much better form. Perfectly spherical and about three-quarters of an inch across, the flower heads erupt along the stem and are quite complex. Each globose cluster consists of many individual flowers: Sets of five petals fused into tubes; long anther stalks; and multiple stamens that carry a tiny spot of pollen at their tips. The overall effect is such that the entire blossom resembles a burst of fireworks, or--as one observer put it--the flower of Little-leaf Sensitive Brier looks like it could have been designed by Disney studios.

Both Mimosa and Little-leaf Sensitive Brier are classified in the Fabaceae (Pea Family), so one should not be surprised to find that seeds from each are borne in pods. Mimosa's fruit ripens in a more typical pea pod (see top photo), while that of Little-leaf Sensitive Brier is produced in a 3-6" spiny, downy, awl-shaped structure in which lies a row of tiny seeds. Members of the Pea Family are also known as "legumes"--plants that harbor nitrogen-collecting bacteria in nodes on their roots. Like soybeans and other legumes, Mimosa and Little-leafed Sensitive Brier help enrich land on which they grow by returning nitrogen to the soil.

Incidentally, one problem native plant enthusiasts will encounter when seeking information about Little-leaf Sensitive Brier is that it has been known by a confusing variety of scientific names. First described by Swedish botanist Jonas C. Dryander in the late 18th century, it was "misidentified" or "rediscovered" so many times that the scientific literature lists a dozen synonyms--the most common being Schrankia microphylla.

To learn more about the subject of this week's photo essay, we also need to dissect its common name: Little-leaf Sensitive Brier. Like many legumes, this plant has compound leaves, but in this case they are doubly compound; i.e., the petiole comes off the stems and is divided into leaflets that, in turn, are divided into subleaflets. These subleaflets are less than a quarter-inch long--hence the name "Little-leaf." The "Brier" part of the name pertains to inconspicuous decurved thorns (above right) that grow along the main vine, on the flower stalk, and on the midrib of the main leaf petiole. In spite of being less than an eighth-of-an-inch long, these briers are quite sharp and can easily lacerate a bare ankle or ungloved hand. (NOTE: A second thorned species, Mimosa quadrivalvis floridana, occurs in the Coastal Plain of Georgia and Florida, while a thornless type, M. strigillosa, grows just in Florida.)

All text, photos & movies © Hilton Pond Center

The most interesting aspect of Little-leaf Sensitive Brier we have saved until last--that being its "sensitivity." If you tap even lightly the leaves of this plant, there is an immediate change in osmotic cell presure that causes leaflets to point away from the main vine and subleaflets to fold in on themselves. This reaction--similar to the closing of a Venus' Fly Trap--occurs rapidly and has the function of protecting leaflets from herbivores by exposing all those sharp little briers. Curiously, a leaflet of Little-leaf Sensitive Brier doesn't have to be touched directly to fold; mere vibration from an adjoining leaf closing can cause an entire vine to fold its leaves in chain reaction. (Double-click on the image below to play a QuickTime movie of wind-blown leaflets folding in response to human touch; note also the small Hoverfly coming in for a sip of nectar.)

When disturbed, most flora simply sit there and take it, but the big Mimosa tree and Little-leaf Sensitive Brier actually respond to their environment. In the case of the tree, its leaves often fold at sunset or during rains and then re-open when the sun strikes them. By comparison, the more complex touch-response in Mimosa microphylla at Hilton Pond Center leads us to think that "plant BEHAVIOR" is a perfectly legitimate term for what happens in the leaflets of our sensitive little legumes.

All text, photos & movies © Hilton Pond Center

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