The Indian Cytotoxic Weed Flora and Their Phytochemicals

India has rich biodiversity and a large number of medicinal plants that are weeds. Usually, weeds are seen as troublemakers in the yard and interfere with the man's land utilization for a specific purpose. Farmers and field botanists recognized these weeds as medicinal plants such as Adonis vernalis, Phyllanthus amarus, Eclipta alba, Centella asiatica, etc. used in folk and indigenous medicines. Most of the plants that are considered weeds have not yet explored phytochemically and pharmacologically. Simultaneously, many of these weeds were reported for their secondary metabolites like alkaloids, glycosides, flavonoids, phenolics, saponins, etc. having medicinal values like anticancer, antioxidant, and anti-inflammatory activities. Many therapeutically important weeds are more popular in India, like Achyranthes bidentata, Artemisia nilagirica, etc. with preferable medicinal benefits such as a diuretic, anti-malarial, and brain tonic. Weeds are storehouses and chemical libraries with simple to complex bioactive secondary metabolites, which serve as drug leads against several resistance diseases like cancer and tuberculosis. Weed biomolecules like Atropine from Atropa belladonna, Berberine from Berberis vulgaris, Colchicine from Colchicum autumnale, Phenoxodiol from Glycine max, Ingenol 3-angelate from Euphorbia species, Combretatin from Combre vulgaris have been reported. This chapter explains various cytotoxic Indian weed flora, reported phytochemicals, drug leads, ethnomedicinal values, modern pharmacology, mechanism of action and clinical safety and efficacy issues.