What are the characteristics of weeds ?
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Characters of adaptation to husbandry practices
- Morphological and/or physiological likeness with cultivated plants
- “Mimicry”: no or little difference from the cultivated plant ; specially in, early stage (weed rice in irrigated rice cultivation).
- Tolerant or resistant to herbicides ( Euphorbia heterophylla or Commelina benghalensis in cotton cultivation).
- Maturity of seeds synchronous to the crop harvest (weed rice or Rottboellia cochinchinensis in rice cultivation)
- Polymorphism of seeds and of the germinal from requirements ( Commelina benghalensis produces 4 types of seeds with, each, a different level of dormancy)
- Discontinued germination for long periods (the germination of Ipomoea eriocarpa seeds is possible all along the rainy season).
- Seed dormancy and longevity in the soil (the seeds of Striga hermonthica can live up to 20 years in the ground)
- Inducted/innate dormancy (in the sudano-sahelian region the seeds of Cucumis melo germinate only from May to July whatever be the conditions).
- Adaptation to husbandry practices
- Multiplication through rhizomes or other vegetative propagation method, favoured by the soil cultural practices, specially disc ploughing ( Cyperus rotundus, Imperata cylindrica…)
- Propagation by cuttings ( Commelina benghalensis, Portulaca oleracea…)
Characters of adaptation to cultural practices
- Fertilization system generally self-compatible ( Commelina benghalensis has self-compatible aerial flowers and cleistogamous underground flowers).
- Pollination by the wind or usual insects ( Poaceae, Asteraceae…)
- High seed production in favourable conditions, but also possible (in a limited way) under conditions of stress.
- A number of types of reproduction ( Cyperus rotundus, Imperata cylindrica seeds and rhizomes, Portulaca oleracea, Commelina benghalensis seed and cuttings)
Adaptations related to the physiology, the growth and to competition
- Rapid growth at the seedling stage ( Rottboellia cochinchinensis)
- High rate of photosynthesis
- Rapid development of the root system
- Rapid partitioning of photosyntates to new leaves
- Rapid vegetative growth to rerach the reproduction stage ( Euphorbia heterophylla can produce seeds four weeks after germination)
- Special "arms" for the competition :
- nitrophilia (species developing in places enriched by nitrogenous elements such as Amaranthus spinosus, Eleusine indica)
- spreading habit ( Commelina benghalensis)
- allelopathy ( Cucumis melo, Tithonia diversifolia)
- Independence from environmental constraints
- Strong acclimatization capacity under variable conditions (phenotype and genotype plasticity)
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