This species is easily the most common of these rare, fragile plants. It reaches heights of 2 ft (61 cm) and grows into a tall bushy green shrub that produces white, highly fragrant flowers.

G. jasminoides is a native of China, and the gardenia most commonly used in Chinese herbal medicine. Its name comes from the fact that it was first introduced to the Western world from Cape Colony in Africa, and the aroma of its large white flowers was said to be very like the scent of jasmine.

http://www.itmonline.org/arts/gardenia.htm

Gardenia (shanzhizi, or simply zhizi) is the fruit of Gardenia jasminoides, one of the frequently used herbs in Chinese medicine. It has an intense bitter taste and a relatively strong cold nature. Yang Yifan has given a detailed description of its qualities and uses:

Gardenia is bitter and cold and enters the heart, lung, and triple burner meridians. Bitterness and cold may clear heat and descend fire. Gardenia can gently and slowly direct heat downwards from the upper burner. It can also promote urination and leach out heat from the heart and lung. It can be used for heat accumulation in the chest, irritability, restlessness, sensations of tightness in the chest, and insomnia.

As the triple burner is the passage not only of qi, but also of water, gardenia enters the triple burner meridian and regulates its function. As bitterness can dry dampness and cold can clear heat, this herb can be used to treat damp-heat syndrome in all three burners-for example, infections of the eyes or eczema on the face and neck caused by damp-heat of the upper burner; jaundice due to damp-heat in the middle burner and qi constraint of the liver and gallbladder; or painful urinary dysfunction due to damp-heat in the lower burner which disturbs the function of the bladder.

Gardenia also has the function of cooling the blood and relieving heat-poison. It can be used in different bleeding conditions, such as nosebleed, hematemesis, and blood in the urine. It can also be applied topically for burns.

In the last paragraph of Yang's description, the mention of "different bleeding conditions" mainly refers to heat in the blood, which is said to cause the blood to become erratic and escape the vessels.

Although most herbalists use the whole dried gardenia fruit, in China the herb material is sometimes differentiated by portion of the fruit selected and the processing method. Dr. Jiao Shude explains (2):

Raw gardenia (simple, dried fruit, as commonly used; shengzhizi) drains fire
Stir-fried gardenia (chaozhizi) and charred gardenia (zhizitan) stanch bleeding
Gardenia husk (gardenia fruit without seeds; zhiziyi) clears heat from the lung and the surface
Gardenia seed (zhiziren) clears internal heat and eliminates heart vexation

In sum, gardenia is used for "all forms of febrile diseases, frenetic movement of hot blood, damp-heat jaundice, and damp-heat strangury (obstructed urination)."

In most cases, gardenia is incorporated into large formulas, where it serves to add or reinforce a fire-purging action. The most commonly used formulation with gardenia as a main ingredient is Huanglian Jiedu Tang (Coptis and Scute Combination), in which gardenia is combined with three other herbs that clear heat and dry dampness: coptis, scute, and phellodendron. The formula is indicated for heat in all three burners (sanjiao), to alleviate symptoms such as fever, irritability, insomnia, bleeding, jaundice, and skin eruptions (3). Gardenia is "directed" to resolve heat in a specific burner by combination with certain herbs. As typical examples: for the lower burner, rhubarb and/or moutan; for the middle burner, scute and/or gentiana; for the upper burner, soja and/or coptis.