1.24.97
Virtual WeedPatch
Weed ID
Psmart.html
Smartweed Family
Smartweed Species-Group
Pennsylvania Smartweed (Polygonum Pensyvanicum)
Ladysthumb (Polygonum Persicaria)
Pennsylvania smartweed and ladysthumb are difficult to differentiate.
In Iowa, we have almost all Pennsylvania smartweed, so that part is easy.
Many are taught that ladysthumb has the purple "ladysthumb" spot
on the leaf, but I have seen so many Pennyslvania smartweed plants (using
all the other features) with the spot that I wouldn't rely on that feature.
This is a demonstration of the first principle of weeds, biodiversity. It
might also indicate cross-fertilization, I am not sure. The best way to
separate these two species is by hairs on the ochrea.
Here (left) is Pennsylvania
smartweed in flower interfering in Michigan barley field.
Another robust Pennsylvania smartweed: 
A young ladysthumb plant with
the distinctive purple thumb mark (left).
Biodiversity in weeds leads to many forms of a plant and plant parts. On
the left are leaves of ladysthumb, on the right leaves of Pennsylvania smartweed.
Notice the different sizes. This could be due to growth conditions (Plasticity:
more water and light and nutrients, the bigger the leaf), or it could be
developmental leaf differences encoded in the plant genes (somatic polymorphism,
a big word for many forms of a plant).
ladysthumb 
Pennsylvania smartweed
Seed & Seedlings
Pennsylvania smartweed
Seed
Notice the small seedlings on the right side of the right picture (photo
credit to Dr. David Staniforth).
Seedlings
Flower color in both varies from white to pink to rose to purplish.
The color of the variant within the species or species-group is not determined
by environment, and is a good example of polymorphism within a species or
species-group. If different colored flowers occur within the same genotype
(probably less likely) it would be somatic polymorphism. More likely, the
different colored flowers are a reflection of genetic polymorphism with
a species or species-group.
ladysthumb 
Pennsylvania smartweed 
