What plants are phytoestrogens?

Phyo = plant, so a phytoestrogen is a natural plant based estrogen. Xeno = foreign, so a xenoestrogen is a foreign or manmade chemical that acts like estrogen. Phytoestrogens are naturally found is herbs, essential oils and foods whereas xenoestrogens are a manmade chemicals and are not naturally found in plants. It is interesting to note that scientist are just discovering that phytoestrogen metabolism and activation in the human body correlates with the health of your microbiome (gut bacteria). 
To answer your question regarding what plants are phytoestrogens, I have chosen to provide you with links to peer reviewed studies that reveal which plants or their components are considered phytoestrogens. While my list is not exhaustive, it will give you a sense of how nature has provided a wide variety of phytoestrogens for our consumption. Evaluate for yourself what researchers are saying about phytoestrogens and form your own opinon about their benefits.
2018 Study
"Phytoestrogens derived from plants exert estrogenic as well as antiestrogenic effects and multiple actions within breast cancer cells. Chemopreventive properties of phytoestrogens have emerged from epidemiological observations. In recent clinical research studies, phytoestrogens are safe and may even protect against breast cancer. In this brief review, the molecular mechanisms of phytoestrogens on regulation of cell cycle, apoptosis, estrogen receptors, cell signaling pathways, and epigenetic modulations in relation to breast cancer are discussed. Phytoestrogens have a preferential affinity for estrogen receptor (ER)-β, which appears to be associated with antiproliferative and anticarcinogenic effects. Moreover, while phytoestrogens not only inhibit ER-positive but also ER-negative breast cancer cells, the possibility of epigenetic modulation playing an important role is also discussed. In conclusion, as there are multiple targets and actions of phytoestrogens, extensive research is still necessary. However, due to low toxicity, low cost, and easy availability, their potent chemoprevention effects deserve further study."
2017 Study
"Great progress has been made in the fight against disease in many different fields of medicine, especially in the field of natural medicine. Phytoestrogens and related compounds play a major role in the prevention and treatment of cancer. Chemoprevention, a narrative approach for controlling cancer, involves the use of specific natural products or synthetic chemical agents to overturn, repress, or prevent pre-malignancy before the development of invasive cancer. Several natural products confer protective effects against a wide range of cancers; examples include grains, nuts, cereals, spices, fruits, vegetables, beverages, medicinal plants, herbs, and their various phytochemical constituents including phenolics, flavonoids, carotenoids, and nitrogen-containing and organosulfur compounds. Phytoestrogens and related compounds act by different mechanisms that ultimately provide benefit with minimum or no side effects and protect and treat different types of cancer, including liver, lung, colon, breast, prostate, esophagus, oral, intestinal, and many other carcinomas."
Foods That Are Phytoestrogens