what kind of diseases? 

This is v very vague question, as is pharmacologically  the concept of blood purification. But it is very present in traditional medicine. In our country a single medicinal plant has many names. We can say that it differs from village to village. Often behind the name is hidden the believed pharmacological effect. One of the names of a very popular plant Hypericum perforatum (Common St John's wort) is blood purifier. The other plant often connected to blood purification is Equisetum arvense (field horsetail, common horsetail or Mare’s tail). The first is mostly used as dry extract, the second just dried and used like tea.

i also introduce tamarind and jujube. i have to mentioned that sometimes utilization of  Common St John's wort can be  induced photosensitive 

Several plant species including Eclipta prostrata, Fagonia indica, Acroptilon repens, Adhatoda zeylanica, Bacopa monnieri, Berberis lycium and many more are used for blood purification in folk or traditional system

I agree with Saeid Davazdahemami, the question is vague. For example leukaemia is disease of the blood specifically a dance of the white blood cells for which Catharanthus roses is effective. Several other plant species are used for anaemia for exampleHibiscus sabdarifa. Others are used for purification, detoxification etc etc

Blood disease is a general term. It may vary from infectious diseases  and  toxemia to allergic conditions, leukemia, hyper lipidemia etc.etc. As er the modern concepts several medicinal plants have  pharmacological properties. In the traditional Indian medicine,  treatment by medicinal plants depends upon the diagnosis by Dosha  in Ayurveda, or Tabiat and Mizaj  according to Unani medical principals.  

For example Blood purifiers may be Anti septic, Disinfectant or germicidal like Accacia catechu, Curcuma longa, Cinnamomum  camphora, Azadirachta  indica,  Aloe vera , Glycirrhizin, while Turmeric may be a good example of a very good  anti-inflammatory as well. Their mode of action may vary from diseases to disease . Excess of Balgham in blood according to   Unani medicine may be of  two to four types eg. due to pus formation or high fat or lipids int he the blood and they may be excreted as per the Unani principals.      

Pl go through the following publication on blood purifiers.

http://www.irjponline.com/admin/php/uploads/1981_pdf.pdf

I agree with the views of the above researchers. Chemicals extracted from periwinkle or catharanthus roseus (white and purple-flowered types) leaves are used for treating certain types of cancer. Piper longum roots and curry leaf plant extracts are used in folk-lore medicine as blood purifiers. 

According to Ayurveda blood disorders will include,bleeding ,clotting,etc.to minimise these/to remove impurities of blood the following herbs are used primarily by ayurvedic physicians

Adhatoda vasica

Tinospora cordifolia

Azadiricta indica

Rubia cordifolia

Symplocous racemosus

Saraca ashoka

Embelica officinialis

Cynadon dactylon

Tridax procumbens

Jyoti given to the point herbals.

Sir,

You may view my articles on RG for your satisfaction.

Thanks.

Article Lantana camara:an medicinal weed.

Asteracantha longifolia

Manjista

The best herbs in Ayurveda considered for Blood purifying is Hemedismus indicus and Manjishta.Most of bitter herbs are considered as Blood purifiers in Ayurveda like Katuki, Guduchi etc. Chandana(Santalum album) Khadira (Acacia Katechu) , Aragwadhadi gana, Shyamadi gana (group of herbs ) etc. explained in Samhithas also act as Blood purifiers.

In TCM DOng QUai is been used as best blood purifier.

@ Dr. Vinesh Kumar

Please take a look at the following RG links and PDF attachments.

Article Plant extracts as an astounding remedy to anemia - A review

Article The potential of medicinal plants in sickle cell disease con...

Article Traditional Herbal Management of Sickle Cell Anemia: Lessons...

Chapter The Potential Effectiveness of Medicinal Plants used for the...

Thesis Medicinal plants used in the treatment of sickle cell diseas...

Article The Effects of Herbs and Fruits on Leukaemia

Article Therapeutic Effect of Blueberry Extracts for Acute Myeloid Leukemia

Thanks!

Check out here also Article Review: Southern African medicinal plants used as blood purifiers