Henna / mehendi a shrub or small tree with dense branches, it is cultivated for its various parts (stem bark, roots, flowers and seeds) that are used in traditional medicine. It grows in tropical and subtropical areas.

Don't confuse henna with henna root (Alkanna tinctoria), also referred to as alkanna root.

Henna is used for stomach ulcers, a type of inflammatory bowel disease (ulcerative colitis), bed sores, and other conditions, but there is no good scientific evidence to support these uses. There is also concern that using henna is unsafe when taken by mouth.

In manufacturing, henna is used in cosmetics, hair dyes, and hair care products. It is also used as a dye for nails, skin, and clothing.
 
Historically, henna has been used for severe diarrhea caused by a parasite (amoebic dysentery), cancer, enlarged spleen, headache, jaundice, and skin conditions. These days, people take henna for stomach and intestinal ulcers.
Henna is sometimes applied directly to the affected area for dandruff, eczema, scabies, fungal infections, and wounds.
In manufacturing, henna is used in cosmetics, hair dyes, and hair care products; and as a dye for nails, hands, and clothing.
People also use henna on the skin as temporary “tattoos.”