五子衍宗丸 Wu Zi Yan Zong Wan is an interesting formula I'd like to share. It's not found in either Bensky & Barolet or the Chen & Chen formula books, nor is it mentioned in Jiao Shu-De's formula book translated by Wiseman et al. (I don't have the 2nd edition of Formulas & Strategies so it may be in that book).
Wu Zi Yan Zong Wan consists of five herbs, all seeds:
菟丝子 Tu Si Zi
枸杞子 Gou Qi Zi
覆盆子 Fu Pen Zi
五味子 Wu Wei Zi
车前子 Che Qian Zi
I first encountered this formula in the Yosan clinic as an intern. My supervisor, Dr. Jin, used it as a base formula to treat infertility in a woman in her early 30's. The full formula had more than 18 herbs, but Wu Zi Yan Zong Wan was where we started. Without any English-language texts that I know of to go on, I'll take a stab at the functions of this formula.
Tu Si Zi tonifies Yang and is often used in fertility formulas. Gou Qi Zi tonifies the Liver and Kidney, Fu Pen Zi and Wu Wei Zi are both in the category of 固涩 gu se, translated as "stabilize and bind" or "astringe". Che Qian Zi is a draining herb but there are several interesting paragraphs in the 2nd edition of the Bensky et al Materia Medica on the use of Che Qian Zi as a Kidney tonic, particularly when used together with herbs that astringe. I won't retype it all here - it starts on page 278, take a look.