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Sweetbay Magnolia

Sweetbay Magnolia

Magnolia virginiana

Magnoliaceae

The Sweetbay Natural Area near the Palm Beach North County Airport is native plant paradise on a beautiful day.  Yesterday was such a day, and the PBSC Native plants class encountered the namesake tree in full sweet bloom.  The overall tree shape and foliage are as beautiful as the blossoms.  They stand out even from some distance as potentially (but not often locally) large, straight-trunked, and with assertive up-tilted branches.  The leaves flutter in the wind revealing white undersides.  Crush them and enjoy the “bay” fragrance.  The branch tips have enormous buds, each covered with a cone-shaped stipule looking like a lopsided dunce cap made by a dunce.

The foliage doesn’t usually show much insect damage.   There are (at least) two natural insecticidal compounds in the leaves, which discourage most herbivores except for the pretty yellow Sweetbay Silkmoth, which tolerates the poison and uses the tree as its larval host.

An old traditional view is that Magnolias have primitive flowers, although modern research has shown that notion to be overstated. The presumed primitiveness manifests as an overall lack of apparent specialization, especially possession of numerous, comparatively leafy-looking floral parts all separate from each other.    Additionally, the pollen, wood, and additional features are interpretable as more or less primitive.  Not many flowers have numerous separate pistils (seed-producing female units) as Magnolias do.  The resulting fruit is a collection of separate units (technically, follicles).  Each unit looks like a tiny leaf wrapped around two bright red seeds.  The gaudy seeds come loose and dangle to entice birds and other hungry agents of dispersal.

What they dangle on is a little interesting.   The water conducting cells in plants are dead, and in some cases they have spiral thickenings allowing them to stretch during growth.  Think of a slinky.  The seeds dangle on the remains of their umbilical cords, stretched slinky-shaped dead cells.

Back to the blossom.  It is big, white, perfumed, and pollinated by an array of beetle species.  Referring to Magnolias in general, the beetles sometimes enter the flower while it is still in bud while those still-closed petals block the “wrong” visitors.  The flowers are female and pollen-receptive at his juncture, with the consequence that they receive the correct pollen by beetle Fed-Ex.   After that, the flowers turn male releasing pollen and open fully.

Sweetbay flower (by JB)

The seeds behave in a way associated with mature or climax forests. Species adapted to mature forests, as opposed to early-succession pioneer species,  tend to have fewer seeds more equipped for shade-tolerance, that is, loaded with food reserves allowing the seedlings to live off of their parents trust fund (food packed into the seed)  until large enough to compete on their own.  Sweetbay seeds tolerate shade, to a point even “preferring ” it according to one study.  Shade favors first-year establishment, although bright light enhances subsequent growth.  In the first year the seedlings can rise two feet in a quest for the light.

Sweetbay Magnolias reach their largest most striking development in undisturbed and unburned wet places.    Yet they get back on their feet aggressively after being knocked down.  They regrow all spunky from fallen trunks, from stump sprouts, and from root sprouts after hurricanes and fires.

After trouble, they tend to reappear in clumps from stump bases, and that may relate to an odd adaptation called a lignotuber, which is vaguely reported for Sweetbay Magnolia without much corroboration (known to me at least).  Lignotubers are specialized survival-zones  at the trunk base.  These have starches and other carbs and nutrients, as well as dormant buds, all ready for post-apocalyptic repopulation.  A more-documented local lignotuber repopulator is the invasive exotic Australian-Pine.

Photo by JB

What about Sweetbays in landscaping?   This might be a topic to start an unwanted argument.   As background,  it might help to know the species is distributed from New England to South Florida and Texas, mostly in wet swampy habitats.  On one hand, there are beautiful examples in cultivation, and the species is abundant in the nursery trade with several names cultivars.  We had a fairly nice one on the PBSC campus, destroyed in a hurricane and a small one there now.  In cultivation, although the tree can flourish in a “normal” residential setting,  I’ve always felt that the specimens at PBSC were never as robust as you might like, probably due to being a little too high, dry, and in one case wind-swept with respect to their natural swampy inclinations.  UF IFAS Fact sheet SF-384 has little reservation about suggesting the species, listed an expected size to be 40-50′ X 15′-25′ good for limited spaces.   The authors hint at issues with “urban tolerance,”  so perhaps a guiding principle on using this species in the landscape is to not duplicate, but at least respect the acid-swampy, semi-shaded origins of this lovely species.

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Posted by on May 3, 2012 in Sweetbay Magnolia

 

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