Weed biodiversity, like spatial and temporal diversity, exists at several levels of plant
organization: all plants of the world all the way down to an individual plant of one
species. Below find a presentation of this type of genetic diversity:
Levels of Weedy Biodiversity within a Habitat
--->Floral Community
------>Species-Group
--------->Species
------------>Population
--------------->Variant: ecotype, biotype, mutant
--->Floral Community
Every agricultural field has, or has the potential, to produce a wide variety of weeds
from its seed and bud bank. Even when we control these weeds for many years, they have the
potential to come back because of the long soil life they have, seed dormancy. Below are
some extreme weed infestations. Can you identify the weeds in each?
------>Species-group
One of the best adapted and known weedy species-groups are the foxtails. Take the
Foxtail World Tour to learn more about the biodiversity
of this troublesome group.
The pigweeds are another infamous species-group. Take a
look at the diversity within this superspecies. Is it any wonder that most weed management
tactics miss at least some of these diverse pests?
The smartweed species-group consists of several species, including ladysthumb and
Pennsylvania smartweed. Below are a variety of leaf shapes and colors from several plants
in this group. They could be from the same or different species, it is hard to tell from
just this picture.
--------->Species
Much biodiversity exists within a single species, intra-specific diversity. Below is a
range of common lambsquarters leaves that could have come from either the same plant or
different plants in this species.
Hedge bindweed has several different colors of flowers within members of the species:
------------>Population
Populations within a species can consist of one or many different genotypes. Below are two
different genotypes (and phenotypes) of quackgrass. The one on the left is a prostrate
growth habit type, the one on the right has upright leaves. These two genotypes exist
within the same field, forming the quackgrass population of that field. Because the
prostrate type exposes more leaf surface to spray applications, often it is the first to
get killed by foliar herbicide applications.
Wild proso millet genotypes produce different colored seeds, some crop seed, some weed seed. Below you can see this variation. Some fields have both, or several different colored seed producing variants. Together they compose the wild proso millet population.
--------------->Variant
Variants of a species can exist together in the same field and comprise that field's
population of that species. Variants can also exist in a field all by themselves, in which
case the population of that species in that field is only one variant, or one genotype.
Below is a collection of different panicle (seedhead) variants of green foxtail. The
panicles on the far left are from the crop foxtail millet. Human selection for types with
big fat seedheads has produced these variants. The panicles on the middle left are from
robust purple green foxtail, very colorful. The picture on the middle right was taken on a
roadside near Madrid, Boone Co., Iowa. Several different colored panicles make up that
site's population. Some are purplish, maybe on their way to being purple robust with time
and selection. The panicle on the far right is from a salt-tolerant green foxtail variant
known as pachy-stachys. It is located in a cozy cove in southern Japan on the Sea
of Japan. Quite a range of variants, don't you think?
--------------->Mutant
There is something dangerously exciting and appealing about mutants. Maybe I feel this way
because I saw too many 1950's science fiction movies in my life, but weird and wild forms
of an organism have an attraction to us all, I am sure. Take a longer look in the mutant
section here in weed biodiversity.
