JP is 100% correct. Hawthorn is not going to do anything to increase vascularity.
When it really comes down to it, vascularity is based on how low your body fat levels are and genetics. The lower your body fat levels, the less adipose tissue stored between your skeletal muscles and skin and the more vascular you will be.
Besides that, the best thing you can do to increase vascularity is to increase muscle fullness. That's why you look more vascular when you are all pumped up in the gym. In order to increase muscle fullness - make sure you are adequately hydrated and eating a diet based on ample amounts of good quality complex carbohydrates. Using a nutrient partitioning supplement to increase insulin muscle insulin sensitivity is also a great idea. Check out n2slin from n2bm.com.