Dogs Beware of the Leafless Swallow-Wort!

12 Aug

Leafless Swallowwort

Cynanchum scoparium


An older synonym for this plant contains the wonderfully apt genus name Amphistelma, meaning “surrounding wreath.”  You’ve got to see it to appreciate the name.  This garland-forming vine, which becomes leafless with age, wraps and smothers its host, as botanist John Kunkel Small noted in his Flora.  The intertwined stems twist together in parallel resembling those twiggy grapevine wreaths in arts and crafts stores.  Too bad about changing nomenclature, because the less descriptive prevailing name now, Cynanchum, merely means dog-choker, relating to the handle “dogbane” applied to related species.  The name “swallow-wort” embraces multiple plants in the Milkweed Family and beyond.  It may allude to toxicity.


Wandering deeper into the speculation zone, the tendency toward leaf loss with advancing age is an apparent adaption to the vine’s changing circumstances along life’s journey.  Youngsters are leafy, as any proper hammock-understory upstart should be.  But eventually the vine climbs a host plant, breaks forth into the sunny overstory, and sheds its leaves, taking on a more xeriphytic, stem-photosynthetic, low-water-loss active adult lifestyle.  Sometimes it resembles the likewise leafless parasitic Lovevine.


Close examination of the small flowers shows them to be Milkweed-ish, that is, having the pollen clumped into packages known as pollinia.   Packaged pollen transfers thousands of grains in a single pollination event.  Not many plants achieve this – with Orchids and Milkweeds (defined broadly) being prominent examples.

The tornado-shaped blossoms have partial barricades at the throat, limiting penetration to the “right” pollinators, whatever they may be.  Butterflies?  Inquiring minds need to know.  Bees and wasps are the only reported pollinators of Cynanchum species known to us, but it is a large genus, and the reports are few and Afro-centric. We prefer butterflies as the prime suspects for those “witch’s hat” flowers, but the truth remains to be seen.

We are dealing with an important insect nursery plant.  The larval guests include the Faithful Beauty Butterfly, first described in Cuba.  Note the species name Composia fidelissima, which predates Fidel Castro, and probably refers to the loyalty of the caterpillar to its vine.  Also in the picture, with details unclear, are the Queen Butterfly and other members of the Monarch Group (subfamily), which  become toxic  from their youthful escapades on Cynanchum scoparium.

The “Giant Milkweed Bug” (Sephina gundlachi) too enjoys today’s vine as its sole breeding host.  Weirdly enough, the mama bug oviposits onto the host plant rather than directly onto the vine.  The bug’s warning coloration is much the same as the Monarch Butterfly and its kin.  This is a possible example of Mullerian Mimicry in which two different noxious creatures mimic each other, reinforcing the effect of their “bug off”  (aposematic, if you will) coloration, much like the black leather, studs, chains and insignia of unrelated motorcycle gangs.

Mullerian Mimic



The double pods split open to release “parachute” seeds, as in most “Milkweeds.”  (This post is a collaborative effort by John Bradford, Billy Cunningham, and George Rogers exploring the eastern shore of Lake Okeechobee. JB shot the pictures, except for the badass.)

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Posted by on August 12, 2011 in Leafless Swallowwort



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