Classification of weeds
- According to ontogeny (life cycle)
A) Annuals: Complete life cycle within a season or year and propagate by seeds. They are again classified as:
i) Rainy season annuals: Come up and tend to complete life cycle during wet season.
Example: Echinochloa spp., Cassia tora, Rotata indica etc.
ii) Winter season annuals: These weeds prevail during cool and dry season.
Example: Chenopodium album, Vicia spp., Anagalis arvensis etc.
iii) Summer season annuals: These weeds appear and complete lifecycle during the hot dry season. Example: Solanum nigrum, Physalis minima etc.
iv) Multi-seasonal annuals: These weeds are capable of growing and completing their lifecycle almost any time of the year due to their photo and thermo non-sensitivity.
Example: Eleusine indica, Digitaria sanguinalis etc.
B) Biennials: These weeds need two years to complete their lifecycle and may propagate either by seed or by vegetative means or by both. Example: Daucus carota, Zingiber casumonar, Plantago spp etc. Generally, these remain vegetative in first year and in the second year they produce seeds.
C) Perennials: These weeds continue their lifecycle within three or more years and produce seeds more than once in their lifecycle. They may reproduce either by seeds or by propagules or by both. Example: Lantana camara, Cynodon dactylon, Agropyron repens, Convolvulus arvensis.
- On the basis of nature of stem
a) Arial or true stem: These weeds have aerial upper ground true stem and are propagated by seeds. These weeds may be woody (Lantana camara) or herbaceous (Argemone mexicana, Chenopodium album etc) type.
b) Sub-aerial with storage organ: These weeds has underground stems with storage tissue which helps them to propagate. Example: Nuts (Cyperus rotundus) and rhizomes (Inula indica).
c) Sub-aerial stem without storage organ: These weeds have subaerial modified stem but have no storage organs such as runners (Oxalis corniculata, Cynodon dactylon) and offset (Pistia spp).
3. On the basis of leaf character
a) Broad leaf weeds (dicot): Chenopodium album, Eclipta alba
b) Narrow leaf weeds (monocot or grasses): Cynodon dactylon, Echinochloa spp.
c) Sedge (narrow leaf but do not belong to gramineae family): Cyperus spp., Fimbristylis spp.
d) Filamentus: Chara and Nitella
- On the basis of plant family
a) Poaceae/gramineae: Eleusine indica, Imperata cylindrical, Echinochloa spp.
b) Asteraceae: Eclipta alba, Tridax, Bidens.
c) Solanaceae: Solanum nigrum.
d) Euphorbiaceae: Phyllaathus, Euphorbia
e) Fabaceae/leguminoseae: Melilotus, Lathyrus, Vicia, Medicago.
f) Chenopodiaceae: Chenopodium album
g) Amaranthaceae: Amaranthus, Alternathera
h) Convolvulaceae: Convolvulus, Ipomoea
5. On the basis of weed association
a) Season bound weeds: They are directly related to the season irrespective to the crop. For e.g. Sorghum halepnse is summer perennial, Crisium arvense is winter perennial.
b) Crop bound weeds: They are parasites of host crop because they depend on their host crop for survival. Some of them are total parasite while some are semi parasite. Example: Orobanche spp. are total parasite on rapeseed and mustard, tobacco and sunflower. Striga spp are semi parasite on maize sugarcane etc.c) Crop associated weeds: These are also crop specific and may be associated with certain crops. They are similar with crop plants due to their similar agro-climatic requirements need for specific microclimate, mimicry, easily contamination of crop seeds with weed seeds. For e.g. Phalaris minor, Avena fatua are specific to wheat, Echinochloa colonum is specific to maize and rice.
