Red Mangrove Youngsters — Failure to Launch

12 Aug

Red Mangroves

Rhizophora mangle


Today John and George sweated like jungle explorers through the Kiplinger Natural Area in Stuart, with distant thunder.  Worth the steambath though, with the blooming Loblolly Bays resembling a Camellia garden.  Even better, Red Mangrove babies were dropping from their mama mangroves onto the crabby Fiddler Crabs brandishing their big claws in the tidal mud.

CLICK to see a nice Mangrove gigapan by John Bradford

Green pencil-shaped Red Mangrove babies (embryos) protruding from the brown fruits. All photos today by JB.

Nothing is more boring than botanical embryology, but we’re going there anyhow.  So grin and bear it, because native plant enthusiasts are duty bound to understand those wacky Red Mangrove youngsters.  They look like big pointy green beans protruding from the much-shorter brown fruits.

To discuss wackiness we first must establish baseline normality. A normal seed is a space capsule where the seed coat surrounds a baby plant (the embryo).  The mother plant packs baby formula called endosperm into the seed and then sends it off to college with no further ado.  The meat and milk in a coconut are examples of endosperm.

Consistent with sociological trends of today, however, the Red Mangrove offspring stays home after college, deriving direct support from the mother plant, just like Kathy Bates doing the laundry for 35-year-old Matthew McConaughey.

In a human family that’s easy enough to arrange, but plants are not designed for extended parental support.  A normal seedling has no way to reach back to the mother plant for supplemental cash.  I mean, the mother plant packs an allotment of endosperm food into the seed, wishes the youngster good luck, and sends it off to fend for itself.  End of connection, end of story.

But not so in a Red Mangrove.  The seed germinates while still inside the fruit, this still suspended from the mother plant.  The germinated youngster (the embryo) grows 8 inches long, requiring vastly more nutrition than the original endosperm.  Here is the weird part: The mother tree conveys sustenance through the fruit into that growing green youngster as it pokes forth from the fruit and enlarges to the size and shape of a pencil.  But how does the maternal nutrition cross the generational barrier?  (Technically, two generations are crossed but who needs pesky details?)  The endosperm is the key.

The endosperm does something amazing, it spills forth from the top of the seed and surrounds the portion of the embryo encased in the fruit as the other end protrudes and elongates.  That is, the endosperm does not function as stored food like it should, but rather reorganizes and becomes a conduit from mother to baby, an umbilical cord.  To display my ignorance as usual, I’m not aware of any other case of this among the flowering plants.

When launch time rolls around, the big green rooty-tooty embryo snaps into two components like the two stages of a Mars-bound rocket.  The fruit-end of the embryo stays behind discarded and embedded in the fruit. The long outer end of the embryo snaps off and drops onto those Fiddler Crabs for tidal dissemination of Rhizophora mangle.  At the breakage point on the dropped embryo portion you see the young leaves twisted into a tight little cone, which had been sheathed in a matching cavity before the break-up.

The part of the embryo that drops free is green on the left, with its pointy conical leaf cluster at the tip. On the right: the green throwaway portion of the embryo (like the hollow cap from a Bic pen) is jutting from the brown fruit. You can see the cavity in the throwaway portion where the conical leaf cluster had been covered before the snap-off.

Who ever heard of endosperm leaving a seed and becoming an umbilical cord?  Who ever heard of a two-stage embryo where one end is abandoned after the other end snaps free?   You have.  Then the next time you tiptoe through the tidal mud you can slice one and know the inside story.

[Notes: For interested readers, the portion of the embryo remaining abandoned in the fruit is the modified pair of cotyledons. The drawing is by Dorothy Marsh, published by S.A. Graham in The Jour. of the Arnold Arboretum 45: 288. 1964.]



Posted by on August 12, 2012 in Red Mangroves


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6 responses to “Red Mangrove Youngsters — Failure to Launch

  1. jacqofhearts

    August 12, 2012 at 5:13 pm

    Who knew? 🙂

  2. George Rogers

    August 12, 2012 at 8:44 pm

    Or who cares….!

  3. Mary Hart

    August 13, 2012 at 3:31 am

    Absolutely fascinating, the rocket simile makes it clear!

  4. George Rogers

    August 13, 2012 at 9:05 am

    Thanks Mary, Are there Mangroves on St. Lucia?


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