try with 

http://www.botanicus.org/title/b11802819

Dear Berioska Quispe,

Thank you so much for the website recomended.

Yordanys, there are a couple of good checklist on weeds for a couple of Neotropical countries. You can get Villaseñor & Espinoza-García 2004 in Diversity & Distribution 10:113-123 for Mexican weeds. Since many weeds are widely distributed you can also try this site http://www.iewf.org/weedid/iewf_front_id.html for Australian plants.

Dear Blanca León

Thanks for your fast response, I will check these literature immediately.