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Results tagged “cornaceae”

Mar 12, 2014: Francis Beidler Forest

Francis Beidler Forest

It was a long day at the workshop today, and an even longer one tomorrow, so another brief entry.

One of my favourite places in my two trips to the southeastern USA, Francis Beidler Forest near Charleston, South Carolina, protects old-growth cypress-tupelo swamp. Both bald-cypress (Taxodium distichum) and tupelo (Nyssa aquatica) are present in this photograph. The base of bald-cypress trees is buttressed (often with accompanying knees), while the base of the tupelo trees seem like swollen trunks (the leftmost two trees completely in the image are tupelo, while the next larger one is a bald-cypress). It is difficult to see in the photograph at this size, but the bark is also quite different: tupelo bark resembles the platiness of some reptile skins, while bald-cypress bark is stringier and forms a bit of a diamond pattern.

Mar 13, 2013: Cornus sanguinea 'Midwinter Fire'

Last weekend, I was in Seattle and had the opportunity to visit the Washington Park Arboretum, the Center for Urban Horticulture (both now administered as the University of Washington Botanic Gardens), and the Volunteer Park Conservatory. It was my first visit to the latter, and though it is quite small, I can see why it was recommended to me by some colleagues. That said, I spent most of my time at the arboretum, as it gave me the best opportunity to retrain myself on some of the technical aspects of photography I've let slip (though this is not on display with these photographs).

Shrubby species and cultivars of Cornus, or dogwoods, are often grown ornamentally for their colourful stems. The best results are achieved when plants are pruned back in early spring; the Missouri Botanical Garden's profile on 'Midwinter Fire' bloodtwig dogwood explains two of the typical pruning options for Cornus (cut everything back to 30cm / 12" or cut back a fraction of the oldest stems each year). The Royal Horticultural Society suggests the latter method, in order to maintain the framework in their profile for this cultivar: Cornus sanguinea 'Midwinter Fire'. Both links contain additional details about the ecology and growing requirements for this particular cultivar. For these keenly interested in shrubby dogwoods for their garden, a broader assessment was published in American Nurseryman magazine, Comparing Cornus (PDF). This assessment was based on evaluations at Longwood Gardens.

The question of why the stems colour has only recently begun to be addressed. A query was made about this last year on the UBC BG Forums: Cornus colour and carotenoid pigments, but unfortunately it wasn't answered with this 2010 paper: Gould, KS et al. 2010. Why some stems are red: cauline anthocyanins shield photosystem II against high light stress. J. Exp. Bot. 61(10):2707-2717. doi:10.1093/jxb/erq106.

Note first of all that it is anthocyanins that are responsible (at least in part) for pigmentation in Cornus, not carotenoids. Secondly, the term "high light stress" is a reference to the evidence that shows that plants can receive too much light. There are a number of detrimental physiological reactions to too much light, but among the most easily explainable is the excess absorption of energy by photosynthetic molecules. This results in the production of ROS, or reactive oxygen species (species being used here as a class of molecules, not in the taxonomic sense). The Plant Biology Stress Lab at Manchester University explains ROS: "These are highly reactive derivatives of oxygen that are capable of reacting with and destroying a wide range of biomolecules including DNA, proteins and lipids".

Gould et al. observed that the high concentrations of anthocyanins in red stems helped these stems to be better protected against excess light levels than plants with green stems, also noting "the redder the stems, the greater was the photoprotective advantage as compared with green stems". This observation was made in 5 of the 6 taxa they experimented with, including a shrubby dogwood species, Cornus stolonifera. The outlier was a cultivar of Lobelia erinus, of which the authors wrote: "[this Lobelia was] bred specifically for a dark purple/blue flower, and its exceptionally high levels of anthocyanins (and chlorophylls) in the stems are the likely outcome of artificial selection by plant breeders rather than of physiological requirement. Nonetheless, the inclusion of Lobelia stems in our study serves to indicate that the photoprotective hypothesis is not universally applicable...There remains much to be learned about anthocyanin function in stems".

May 10, 2011: Cornus florida

Cornus florida

A bit of a silly common name for this small tree, flowering dogwood (all dogwoods of reproductive age have flowers...), but that shouldn't detract from its springtime elegance. Cornus florida is another native of the eastern USA, but also nudges into Canada at the extreme edge of southern Ontario. A subspecies, Cornus florida subsp. urbiniana, is only found in eastern Mexico.

Cornus florida is threatened throughout much of its range thanks to the introduction of a fungus in the mid-1970s, Discula destructiva. Fungal infection of these dogwoods causes the disease dogwood anthracnose. Infection may or may not be terminal for individual trees, but it also weakens the trees and makes them susceptible to insects or other diseases. Over a long period of time, as random events occur and accumulate, significant mortality may result and this seems to be indicated in Jenkins, M. and White, P. 2002. Cornus florida L. Mortality and Understory Composition Changes in Western Great Smoky Mountains National Park. Journal of the Torrey Botanical Society. 129(3): 194-206. Jenkins and White found that higher relative mortality occurred over the two or so decades from 1977-1979 to 1995-2000 with smaller trees, and in cove forests and alluvial forests.

Read more about Cornus florida via the Silvics of North America or see additional photographs via the USDA PLANTS database: Cornus florida.

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