Root Parasites—Green Mammals?

26 Oct

Black Senna  

Seymeria pectinata


Yesterday John and George tiptoed through the toadstools the Seabranch State Park near Hobe Sound.   The area we explored is a coastal upland scrubby pine woods, and it was beautiful in the comparatively “cool” October morning.  Much of the area is in the light shade of a mixed-species pine canopy, with a carpet of white and green lichens around an odd scattering of Giant Airplants (Tillandsia utriculata) with inflorescences rising from the lichen-lawn vertically 6 feet or more.  Mushrooms were abundant and Keebler-Elf-ish.  Adding to the splendor of it all were flowering Liatris and Polygonella species…a celebration of blooming nature in its vibrant glory.  So why is today’s topic is a dead, black, root-parasitizing annual in its autumn death mode? (Hey, for pretty flowers there are blogs aplenty.)

Black Senna on white sand (floral photos taken earlier in year, by JB)

Black Senna on white sand (floral photos taken earlier in year, by JB)

Black Senna belongs to the plant family probably having the largest proportion of root-parasites, the Orobanchaceae.  We have a lot of known root parasites in Florida, and no doubt several undiscovered, especially if you allow indirect fungal connections in addition to direct assault of one root on a neighbor, as we’re examining today.  Most famously and conspicuous are plant species so dedicated to theft they do not even bother to make chlorophyll, for instance in our area  Squawroot (Conopholis)  and Indian Pipes (in the Azalea Family) as well as many other non-green parasites elsewhere in Florida.  The shrub Hogplum (Ximenia americana in the Ximeniaceae) practices the same, and makes green leaves (or greenish-yellow) leaves too.  We have drifted so let’s return to the Orobanchaceae.

Black Senna (JB)

Black Senna (JB)

Several Orobanchaceae look like “nice” wildflowers but snitch nutrition and water secretly from the roots of law-abiding neighbors.  Witchweed (Striga) is a widespread crop-destructive parasitic genus so good at theft it can survive in the dark if its host is in the light.

Common on our botanical outings is American Bluehearts (Buchnera americana),  which should be called instead, “American Sneak Thief” for its subterranean larceny.

American Sneak Thief (JB)

American Sneak Thief (JB)

More pretty little parasites are the False-Foxgloves, the many species of Agalinis in Florida and beyond.

Agalinis (JB)

Agalinis (JB)

Yaupon Black Senna (Seymeria cassioides) is a pine-tree root parasite causing commercial losses, and thus well studied.  Its young seedlings die if they do not make effective contact with pine roots early in life (unless perhaps the mother plant helps out—stay tuned).  The southern limit of Yaupon  BS is probably  just a tad north of where John and I botanize, but no worries, we have our own local Black Senna, Seymeria pectinata, also parasitic but not studied much.  A glance at one in fruit shows vast numbers or small seeds scattered to find a victim, probably failing to survive without quick host contact.  The plant is an annual, and its distribution is clumpy, reflecting perhaps good spots for snagging host roots.

Black Senna (S. pectinata) root haustoria (root-sucking organs) on BS roots yesterday (JB).  The suckers are the parts that look like the business end of a plumber's plunger.

Black Senna (S. pectinata) root haustoria (root-sucking organs) on BS roots yesterday (JB). The suckers are the parts that look like the business end of a plumber’s plunger.

While wondering how a parasitic annual manages to survive from year to year, here is something to ponder:  In some root parasites the seedlings reportedly latch temporarily onto the long-suffering and self-sacrificing mother plant for nourishment until they graduate to a proper host of their own.  Whether or not this occurs in Seymeria is for somebody’s future Masters Thesis.  I never like those anthropomorphic books attributing plants with animal-like qualities, but nursing the young is pretty impressive for a lowdown root-sucking weed.

Hungry Witchweed seedling attaching to corn root (by RJ Musselman SIU)

Hungry Witchweed seedling attaching to corn root like a tick on a dog (by RJ Musselman SIU)


Posted by on October 26, 2013 in Black Senna


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2 responses to “Root Parasites—Green Mammals?

  1. Mary Hart

    October 28, 2013 at 5:35 am

    These are fascinating plants – UK has its share. Red Bartsia and Yelow Ratle in Scophulariaceae and bromrape in Orobanchiaceae for instance.

  2. George Rogers

    October 28, 2013 at 9:38 am

    Thanks Mary, I’ve got to look up Red Bartsia…a new one for me. Did the big storm hit?


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