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Redbud Seedpods Hold Surprises W University of Richmond UR Scholarship Repository Biology Faculty Publications Biology Fall 2013 Redbud Seedpods Hold Surprises W. John Hayden University of Richmond, [email protected] Follow this and additional works at: http://scholarship.richmond.edu/biology-faculty-publications Part of the Botany Commons, and the Plant Biology Commons Recommended Citation Hayden, W. John. "Redbud Seedpods Hold Surprises." Bulletin of the Virginia Native Plant Society 32, no. 5 (Autumn 2013): 1, 6. This Article is brought to you for free and open access by the Biology at UR Scholarship Repository. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of UR Scholarship Repository. For more information, please contact [email protected]. Vol. 32, No. 5 Autumn 2013 ISSN 1085-9632 A publication of the VIRGINIA NATIVE PLANT SOCIETY http://www.vnps.org Conserving wild flowers and wild places Redbud seedpods hold surprises As fall advances across the Old tion would leave redbud seedlings vul- Dominion, canopies of redbud, the nerable to the harsh rigors of winter; 2013 VNPS Wildflower of the Year, better to remain dormant through the transform themselves from green to coldest months and germinate during gold, revealing seed pods also chang- the more favorable weather of spring. ing color from pale green to dark choco- Most legumes have very hard seeds, laty brown. These seedpods, which may and redbud is no exception. Anatomi- be retained on the tree into winter, are cally, the stereotypical legume seed coat typical legume fruits, the product of the consists of two (or more) layers of tough flower’s simple pistil, each containing sclereid cells: elongate macrosclereids several seeds. Unlike most legumes, at the surface underlain by one (or more) however, redbud seed pods seem dis- layers of boxlike brachysclereids di- inclined to open and release individual rectly below. Both of these sclereids are seeds for dispersal. Redbud fruits tend very nearly solid masses of cell-wall to disperse intact. Once on the ground, material. Together, they tile the surface the inevitable action of weather and of the seed, except for a small patch microbes gradually degrades the pod, known as the hilum, which marks the whereupon the process of seed germi- (See Redbud, page 6) nation can proceed. Fresh seeds of redbud, however, are dormant and will not germinate until two different factors, each re- sponsible for different as- pects of seed dormancy, are overcome. This double dor- mancy derives from the presence of an extremely hard, impermeable, seed coat and physiological dor- mancy of the embryo con- tained within. For temper- ate-zone trees, seed dor- mancy makes good ecologi- cal sense. Rapid germina- Redbud seedpods. (Courtesy John Hayden) Bulletin of the Virginia Native Plant Society • Redbud Redbud seeds that escape being for one or two months before returning (Continued from page 1) eaten by weevils eventually find them- to warm conditions. In nature, the spot where the seed attaches to the seed selves in the soil. Time passes, rain and physical (seed coat) and physiologi- pod. These tightly packed sclereids con- snow come and go, temperatures climb cal (embryo) dormancy may be over- stitute an impermeable barrier to water, and fall, and ubiquitous microbes se- come in the course of a single winter. and, as long as water is excluded, the crete their digestive enzymes, all of But based on personal experience, seed will remain dormant. which gradually break down the seed passage through a second winter sea- Besides dormancy, the tough seed coat and water gains access to the in- son yielded many more redbud seed- coats of legumes also provide a mea- terior of the previously very dry seed. lings than the first—perhaps it took sure of protection from seed predators. In this way, nature breaches the physi- that long for both dormancy factors to For plants, rich stores of food, usually cal dormancy of redbud seeds. be overcome. starch, or protein, or oil, assist in es- Impatient gardeners can speed up It has been said that wishes are like tablishment of the new seedling. But seed hydration in a number of ways. seeds—few ever develop into some- the world is full of hungry animals, Sandpaper, files, or sharp knives can thing. Indeed, we should expect, on and many (including us humans) have be used to nick into the seed coat, pro- average, each redbud tree to succeed in learned how to exploit the nutrients viding pathways for the quick entry of making just one redbud seedling that contained in seeds. Very few people, water. For the chemically inclined, brief will survive to maturity—any less and however, eat wild-collected legume treatment in a strong acid can also the species would eventually go extinct, seeds; toxins and tough seed coats ren- soften the seed coat and promote per- any more and we would be overrun der wild legume seeds essentially in- meability. These techniques, either with redbuds. It is a sobering proposi- edible. But we can eat seeds of various mechanical or chemical, are known as tion to think that the despite the elabo- crop legumes (e.g., beans, peas, scarification. And to hasten water en- rate biology of redbud seeds, despite chickpeas, and soybeans) because dur- try, redbud seeds can be soaked in their double dormancy adaptations for ing the process of domestication, our warm water prior to planting. proper germination, their structural ancestors selected less toxic and softer Mere hydration of redbud seeds, and chemical defenses notwithstand- seeds from the natural variability of the however, is not sufficient to prompt ing, and despite the undeniable fact wild legume ancestors of these crops. germination of the embryo because that each has the genetic potential to But one group of animals is espe- there is also a physiological dormancy become a handsome redbud, only a tiny cially adapted to eating wild legume factor that must be overcome. Hy- percentage of the seeds produced can seeds, a group of beetles known as bean drated redbud embryos must endure be expected to become trees themselves. weevils (family Chrysomelidae, sub- several weeks of cool temperature fol- Redbud seeds may seem like such family Bruchinae). Adults of these in- lowed by a return to warmth before they simple little things, but close examina- sects live in flowers, consuming pol- germinate. In a horticultural practice tion reveals unexpected intricacies. One len and nectar. After mating, females called cold stratification, scarified red- is reminded of a saying by the Chinese lay their eggs inside the ovary of the bud seeds can be induced to germinate philosopher, Lao Tzu (Laozi), “To see flower. As larvae emerge from their relatively quickly by sowing in moist things in the seed, that is genius.” eggs, they enter the plant’s ovules, soil and keeping the pot refrigerated W. John Hayden, VNPS Botany Chair which at this early stage are soft and unprotected. An infected seed develops more or less normally; but as it reaches maturity, the hungry weevil larva (al- ready inside) consumes all the inter- nal tissues. Just before pupation, the weevil larva cuts an exit hole through the seed coat, again, working from the inside. There are well over 1,000 differ- ent species of bean weevils, including specialists that attack just a single host plant, and generalists with more catho- lic tastes. Most hosts are legumes, but some weevils also attack plants in the mallow (Malvaceae) and morning glory (Convolvulaceae) families. The weevil Gibbobruchus mimus is commonly encountered in eastern redbud seeds. Page 6 Autumn 2013.
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