There is often discrepancy when considering where weeds
belong in the evolution of domesticated species from wild ancestor species. It
is known that classes of wild plants and animals have merged into the domestic
class by continuous stages in the degree of their intimacy with man. Wild is
thought of as plants that do not require human cultivation, flourish in the
natural, undisturbed environment and cannot invade permanently man-disturbed
habitats whereas domesticates cannot survive in the ‘wild’ due to intense
selection and they require cultivation and continuous help to propagate within
a human control environment. Weeds also flourish in man-made environments,
however they don’t require cultivation. Where do weeds come from? De Wet & Harlan (1975) define weed evolution
under three methods: - as successful colonizers selected for continuous habitat disturbance in a man-made habitat
- as derivatives of hybridisation between wild and cultivated species
- and through selection towards re-establishing seed dispersal mechanisms in abandoned domesticates
Weeds and domesticates differ in the degree of dependence on
man for success in permanently disturbed man-made habitats. Some seed crops
have hybridised with their ancestral races to produce weedy derivatives
wherever wild and cultivated species are sympatric. This leads to weed sunflowers,
weed carrots, weed maize and weed watermelons.
Domesticates can be weedy (when no longer cultivated) and
weeds are sometimes grown as crops. However weeds never require artificial propagation.
They are capable of establishing new populations within the disturbed habitat without
further help by man. Most of our common
weeds are Eurasian in origin such as dandelion (below) and crabgrass and occupy an
array of niches such as some are strictly associated with agriculture.
 |
| Common Australian Weed: Dandelion TARAXACUM SP |
‘Weediness’ is not only confined to plants as numerous animal
species have weedy races. For example: worldwide houseflies, rabbits in Australia,
the Brahman cow in India, and most shocking humans are the ultimate weed being obligated
and confined to the habitat he is creating.
Image accessed 27/05/14: http://aggregata.blogspot.com.au/2013/03/dandelions-weed-medicinal-herb-and.html
I didn’t think that weeds were that complex! I would never even have considered that weeds could be domesticates. You mention that weeds and domesticates differ in their degree of dependence on man, so does this mean that weedy carrots (for example) don’t actually rely on man? You also mention that man is the ultimate weed, but this begs the question as to whether we, ourselves, are wild or domesticated? Interesting thoughts.
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