Plants with Anthraquinones provides a laxative for the large intestine. It creates contractions in the intestinal walls facilitates a bowel movement in about 10 hours from ingestion. The chemical itself is manufactured and widely used as a vat dye used for textiles.
Use
Constipation, textile dye
Plants
Aloe, Rhubarb, Senna
Personal Experience
I rarely have to use a laxative herb since I've minimized the consumption of carbs. I also tend to eat vegetable that have diuretic properties which cleans my intestines regularly.
Useful Links
Thenaturopathicherbalist.com describes anthraquinones and its uses very thoroughly
National Institute of Health explanation on molecular composition and its usage as a dye.