TAXACOM Digest - 11 May 1995 to 12 May 1995

[Scott Ranger]

> Date:    Fri, 12 May 1995 09:19:21 -0400
> From:    Bill Williams <bwilliam at OYSTER.SMCM.EDU>
> Subject: Poison Ivy
>
> What's the proper scientific name for the poison ivy commonly found in
> Maryland?  Brown and Brown's "Woody Plants of Maryland" uses "Rhus radicans
> L.," but many locals seem to think it should be "Rhus toxicodendron L.,"
> which Brown and Brown call "poison oak," and say is "uncommon."

> William E. Williams, bwilliam at oyster.smcm.edu
> Department of Biology
> St. Mary's College of Maryland
> St. Mary's City, MD 20686

John Kartesz' "A Synonymized Checklist of the Vascular Flora of the
United States, Canada, and Greenland" 2nd ed, 1994 recognizes poison
ivy (eastern US species) as

   Toxicodendron radicans (L.) Kuntze
      ssp. divaricatum (Greene) Gillis
          [syn: Toxicodendron  radicans var. divaricatum (Greene) Barkl]
      ssp. eximium (Greene ) Gillis
          [syn:  Rhus toxicodendron L. var. eximina (Greene) McNair]
          [syn:  Toxicodendron radicans var. eximium (Greene) Barkl]
      ssp. negundo (Greene) Gillis
          [syn:  Toxicodendron radicans var. negundo (Greene) Barkl]
      ssp. pubens (Englelm. ex. S. Wats.) Gillis
          [syn:  Toxicodendron radicans var. pubens (Engelm. ex. S.  Wats.) Gillis]
       ssp. radicans
          [syn:  Rhus radicans L.]
          [syn:  Ruhs radicans var. littoralis (Mearns) Deam]
          [syn:  Rhus radicans var. malacotrichocarpa (A.H. Moore) Fern]
          [syn:  Toxicodendron vulgare P. Mill]
       ssp. verrucosum (Schele) Gillis
          [syn:  Toxicodendron radicans var. verrucosum  (Scheele) Barkl]

The eastern species called "poison oak" is ascribed to:

  Toxicodendron pubescens P. Mill
          [syn:  Rhus acutiloba Turcz.]
          [syn:  Rhus toxicarium Salisb.]
          [syn:  Toxicodendron quercifolium (Michx.) Greene]
          [syn:  Toxicodendron toxicarium Gillis]
          [syn:  Toxicodendron toxicodendron (L.) Britt.]


The two species are clearly closely related, but can be field
separated without much difficulty.  Here in Georgia, poison oak tends
to prefer dry, rocky, hot sites and grows predominantly as a short
shrub.  The leaves are more "oak-like."   Poison ivy grows just about
anywhere the ground is a bit disturbed (even the slightest) and has
many, many forms as the list of subspecies might indicate).

Hope you find this helpful.
"That which is, is.  It is justified only by being."

Scott Ranger
ranger at america.net