[Trillium-l] Trillium erectum x flexipes

Fern Hill fernhill at voicenet.com
Tue May 17 05:00:39 CEST 2011

I think Jim has a good and valid point.  My late wife and I were Mt Cuba Guides when Dick was director.  On one outting he took the guides to look at the Susquehanna trillium from, as I recall, the Conowingo Dam in the south to near Harrisburg in the North.  We visited a site near either Conowingo or Holtswood dams where there was a sparce (due to restricted habitat) trillium population on the west side of the river  At Shenk's Ferry the big population is on the East side while across the river from Shenk's Ferry at otter Creek there is a large population on the West.  The North population South of Harrisburg was nearly extripated by someone beginning a garden, but a few plants remained under brush piles in a small ravine on the West side of the river just as its stream entered the river.  On other ocassions Janet and I were shown some trillium population NE of harrisburg by friends.   

Dick's hypothesis is that the Shenk's Ferry population in particular was - as Jim said - a relict population that resulted from hybridization of red erectum with flexipes followed by back crossing with flexipes.  He observed that North  (the Harrisburg) site had a high concentration of pinkish and off-white plants while further North the trillium were all red erectums.  My memory is that the Otter Creek population had somewhat smaller flowers and looked more flexipesish than Shenk's Ferry and south.  I recall no colored forms South of Shenk's Ferry or at Otter Creek.  On rare occasion Shenks Ferry produces a speckled pinkish form and the ovaries vary as Jim indicated.  

There are some historical points that need to be considered before the hybridization hypothesis is fully accepted.  At Shenk's ferry the population is not entirely "natural"  The Glen there was the site of a lot of industrial activity in the 1800's.  There was an active inn - probably at the flat area at the base of the entry hill.  A rail road cut across the glen about half way up and further up there is the foundation of a cigar factory and what may be the remnants of an exploded dynamite factory.  When that went up nearly 20 workers were killed.  The area near my research site was at some point planted to regular rows of white pine trees that are now beginning to die out.  All this indicates that the site overall has suffered considerable human disturbance.  Trillium on the steep glen sides were probably the source of seed that repopulated disturbed areas.  In other words much of Shenk's ferry is the result of active trillium colonization and reproduction.  Because of the width of the river, farming in the uplands, and rahter abrupt changes in the underlying geology the trillium populations - particularly at Shenk's ferry - would be genetically isolated.  The result of isolation and rapid sexulal propagation (rapid that is for trillium) is a way of establishing a local form and bringing out variation in form.   

The possibility of geologic influence needs a bit more consideration too.  As one goes North along the river, I believe that rock types appear that are distinctly more acidic than the bedrock at Shenk's Ferry.  Acidic conditions favor the red Trillium erectum.  Introgression of forms would be most likely to happen near where there is a change in the acidity of the country rock.  The Harrisburg site is more likely such an area than is the Shenk's Ferry location.  Then to complicate things more there is glaciation.  The ice did not reach Harrisburg or Shenk's Ferry, but the isostatic uplift caused by glacial weight further North raised the land level along the Southern Susquehanna (and Potomac) enough to allow the river to create a canyon - most of which is now used for hydropower.  This rise in elevation also rejuvinated side streams and left "benches" of aluvial soil still visible at Shenk's Ferry.  These features were probably more fertile and contain more available Ca and Mg which the flexipes types of trillium seem to like.

Certainly hybridization is possible and is probably responsible for the color swarm near Harrisburg. but at Shenk's Ferry I think that other historical factors are involved as well.

My gracious - I am beginning to go on near as long as Richard used to.

John Gyer  Clarksboro  NJ USA

  ----- Original Message ----- 
  From: Jim McClements 
  To: Trillium Enthusiast Discussion List (and other Woodland plants) 
  Sent: Monday, May 16, 2011 4:56 PM
  Subject: Re: [Trillium-l] Trillium erectum x flexipes

  The subject of Trillium hybrids, particularly in the "erectum complex", should certainly include consideration of what I often refer to as the "Susquehanna Trillium", found by the thousands in spectacular hillside masses at Shenk's Ferry PA, but also on both sides of the Susquehanna River in the same general location. Most trillium addicts in my area (Pa, NJ, and Del) are quite familiar with these.

  The best guess (by Dick Lighty, formerly at Mt.Cuba Gardens) about these is that they probably represent a relict hybrid between white T. erectum and T. flexipes. They are 99.99% white petalled, but with ovary color ranging from white (like flexipes) to black (like erectum), and some variation in shape. Aside from ovary color the plants are pretty much uniform. I have quite a few of these in my garden (grown from seed), where they are quite vigorous and show the same ovarian variations as the wild population.

  Could this be the source of the "erectum/flexipes hybrid" that started this thread of discussion?

  Jim McClements

  On Mon, May 16, 2011 at 1:39 PM, Lis Allison <garden at pine-ridge.ca> wrote:

    On May 16, 2011, The Grahams wrote:
    > I am curious as to what you see as color forms if any beyond the red,
    > white, and yellow "pure" forms. I am wondering if what "others"
    > consider to be "hybrids" because they are pink or picotee or such
    > might be natural diversity?

    Definitely we have pinks, all shades, and some that could be called
    'picotee'. I photographed one just last Friday. It was cream, maybe a
    touch of yellow, with a dark red edge and red vein lines.

    > Just as another point of curiosity, what about variation in flower
    > size? If you mentioned flower size, I missed that.

    Lots of variation, but it is hard to know how much is due to the plant's
    maturity. Young plants have much smaller flowers than older ones. Also, I
    have a few plants in my garden with fairly wide, rounded petals. Most are
    pointed and strap-shaped, but not all. Similar to T. grandiflorum in that.

    One T. grandiflorum flower this Spring is a full 6" across. The T. erectum
    flowers are smaller, up to 4" across.

    > Very intriguing to learn that you have a LOT of diversity in what
    > "should be" only erectum.

    Funny, I always thought of T. erectum as being the one that had a lot of
    variation! The T. grandiflorums here don't seem to vary much - if you
    ignore size - but the Reds sure do.

    Elisabeth Allison
    Pine Ridge Studio
    website: www.pine-ridge.ca
    Pottery blog: www.studio-on-the-ridge.blogspot.com
    Garden blog: www.garden-on-the-ridge.blogspot.com

    Lis Allison
    Pine Ridge Studio
    Garden blog: www.garden-on-the-ridge.blogspot.ca

    Trillium-l mailing list
    Trillium-l at science.uu.nl


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