Hedysarum: poisonous or not?

One of the few sources of starch in the boreal forest of Interior Alaska is the root of the common species Hedysarum americanum (Michx.) Britton, known as “troth” in Lower Tanana (Kari, Lower Tanana Dene Dictionary) and in English as “Indian potato” or “Eskimo potato”. However a similar species, Hedysarum mackenziei Richardson (“tsoni trodha'”; Kari, LTDD), co-occurs with americanum, and is apparently poisonous. Telling the two species apart is vital if you will be harvesting the root of americanum. Fortunately there are may characters to assist:

• Hedysarum mackenziei:
  • Inflorescence overall shape shorter and rounder
  • Petals usually dark purple
  • Upper calyx lobes long and thin
  • Banner petal about same length than wing
  • Secondary veins invisible on leaflet lower surface
  • Veins on loment with a dominant transverse orientation
  • Loment more circular
• Hedysarum americanum:
  • Inflorescence overall shape long and narrow
  • Petals usually pale purple
  • Upper calyx lobes short and triangular
  • Banner petal shorter than wing
  • Secondary veins clearly visible as black lines on leaflet lower surface
  • Veins on loment net-like, without a dominant transverse orientation (this is the most important character, since there may be no flowers or leaves when you are harvesting)
  • Loment more elliptical

Further information:

• Hultén
• iNaturalist (note that the name used in iNat for Hedysarum mackenziei is Hedysarum boreale, and for Hedysarum americanum is Hedysarum alpinum).
• Guide to the complex nomenclature. In this article I’m using the names according to the Panarctic flora.

As an aside, Hedysarum americanum is one of my favorite species in Alaska: it’s the one with leaves that most remind me of the frequent pinnate, entire leaves of tropical forest.

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