Willow Herb,

The Willow herb is considered a common weed but may have potential benefit in prostate disorders. Oenothein B, a substance in willow herb, appears to have 5-alpha-reductase inhibitory activity.


Inhibition of 5 alpha-reductase and aromatase by the ellagitannins oenothein A and oenothein B from Epilobium species.
http://www.ncbi.nlm.nih.gov/pubmed/9140222


Epilobium angustifolium : 5-alpha-reductase and aromatase by the ellagitannins oenothein...
http://www.fitnessbanter.com/showthread.php?t=3120

http://en.m.wikipedia.org/wiki/Epilobium


Not the same genus:

White willow
http://en.m.wikipedia.org/wiki/White_willow

Another 5 AR's

Inhibition of 5 alpha-reductase activity in human skin by zinc and azelaic acid.
http://www.ncbi.nlm.nih.gov/pubmed/3207614

Effects of sex steroids on skin 5 alpha-reductase activity in vitro.
http://www.ncbi.nlm.nih.gov/pubmed/1828548