The following herbs showed potential as medicinal plants to improve fertility and testosterone production; these assessments were based primarily on animal studies:

Celery (Apium graveolens): Celery extract improved sperm production in rats after 60 days of supplementation.
Camphor (Cinnamomum camphora): Plant stem extract increased luteinizing hormone and decreased follicle-stimulating hormone in rats after 30 days. However, testosterone was not increased.
Cornelian cherry (Cornus mas): The fruit extract of Cornus mas showed antioxidant and anti-inflammatory properties in rats. Sperm and testosterone production were not investigated.
Satureja (Satureja khuzestanica): The essential oil of the plant’s aerial parts improved fertility and litter size in rats.
Ashwagandha (Withania somnifera): Human intervention trials suggest that ashwagandha improved semen quality in men.
Indian fumitory (Fumaria parviflora): Leaf extract restored reproduction and reduced testicular toxicity after lead exposure in rats.
Ginger (Zingiber officinale): Ginger powder increased sperm percentage, viability, motility, and testosterone levels in animal and human studies.
Ceylon cinnamon (Cinnamomum zeylanicum): Ceylon cinnamon improved sperm production, motility, and viability in rats.
Date palm (Phoenix dactylifera): Fruit extract of date palm improved sperm motility in rats and humans.
Nigerian walnut (Plukenetia conophora): Fruit seed extract improved sperm count, motility, and viability in rats. Also, testosterone was increased.
Bitter kola (Garcinia kola): Bitter kola extract reduced testicular toxicity after lead exposure in rats.
Coconut (Cocos nucifera): Coconut oil reduced testicular toxicity after lead exposure in rats.
African baobab (Adansonia digitata): Extract of African baobab attenuated the negative effects of cadmium ions on the testicles in rats.

Medicinal plants to improve fertility and testosterone production? Original paper