What is the botanical difference between a weed and a grass?

Question

I mean differences in cellular structure, reproductive features... anything that's different really.

Answer 1

You can ask what the weedy genetic traits are that differ from domestic traits in plants. Plants have been selected for specific characters that make cultivation easier while wild versions of the plants retain all the weed traits. Peas are a good example. Mendel use wild traits in contrast to domestic in his breeding experiments.

Wild peas have pods that open to spill the seeds, they are dehiscent. The seeds have a dormancy period. They are tall with many basal branches. The seeds have poor taste color and texture. Their flowering is triggered by long day length.

Domestic peas do not have pods that open (indehiscent) so they don't spill their seeds after picking and seed dormancy is lacking so they germinate more reliably. The plants are dwarf with few basal branches. The seed quality is superior in taste, color and texture. Flowering is day neutral they lack photoperiodicity.

Do any of these traits sound familiar? Tall versus dwarf, seed coat wrinkled versus round. Domesticated traits are often the recessive alleles in in the original plant. Selective breeding produced homozygous plants for the qualities so they now breed true.

Mendel was working with the traits that form the basis of pea domestication from the wild type. In fact the domestic legume family all show similar changes from their wild counterparts. Like animals, plants share certain traits when they become domesticated because we select them for the same features each time.

Domestic grass traits

Domestication traits pre-harvest sprouting and dormancy (germinability) in wheat.

http://www.ingentaconnect.com/content/kl...

"differences between pearl millet (Pennisetum glaucum ssp. glaucum) and its wild ancestor (Pennisetum glaucum ssp. monodii, form mollissimum)"

http://cat.inist.fr/?aModele=afficheN&cp...

Answer 2

I'm afraid your question is nonsensical.  A grass is a member of a particular plant group; grasses.  All grasses share anatomical characteristics.  A weed, on the other hand, is any plant growing in a place where the gardener or farmer doesn't want it.  Weeds aren't a botanical category.

Any plants can be weeds, and they can all differ from one another in cellular structure, reproductive features and so on.  Grasses can also be weeds.  I just pulled some out the strawberry bed this afternoon.

Answer 3

Weeds are what you or the farmer do not want to grow. Generally they are broad leafed, dicots.

Grasses include all the grains, which are monocots.

Many people do not want grasses growing in their garden.

Plant cells are much the same. Tissues vary depending on use.

Answer 4

They are monocots and weeds are unwanted while grass is grown with the farmer's knowledge ..