I wonder how many useful plants have been lost through the centuries. The Romans drove a plant to extinction that acted as a birth control. I read an article that India has lost more than 3000 medicinal plants over the centuries, and there are dozens of critically endangered ones. There are dosens of native American plants that have gone extinct, and more that are endangered.
I once interviewed the last medicine woman of the local band of Muskogee. She showed me a journal of a previous medicine woman that contained a single, pressed, blue flower. The flower cured migraines, among other things, and only grew in one area of Escambia County. When the government built the Indian school in the early 20th Century, they bulldozed the area where the flower grew, and they never came back. The current medicine woman had had her flower analyzed to see if it grew anywhere else, or even had a name. Nope, it was a novel species.
I also read that we only have a fraction of the plant diversity that they had a century ago, and previous generations suffered from less diversity than their fore-bearers. (Actually around 1/4, What is Agrobiodiversity?
Just since the 1950s we have lost several banana, apple (86%, What is Agrobiodiversity?
), fruit and vegetable varietals due to over-harvesting or blight, as well as several species of fish due to overfishing. Flipping through any good vintage cookbook you are bound to find something that has to be substituted. Even the milk and cheese we get has less diversity than just 40 years ago (How Globalization and Climate Change Are Taking Away Our Favorite Foods
We lost a popular variety of pear around 1920, the most popular type of banana in 1965, and countless varieties or tart apples and persimmon over the last 200 years. Chocolate, agave, Arabica coffee beans, peanuts, several species of wine grape, honey, avocado, and maple syrup are the most likely losses over the next 30 to 100 years.
It's even worse when you think about the meat that has gone extinct, or even "cheap" meat that has become expensive luxury due to increased rarity.