What comes to mind with the phrase “endangered species”? Elephants. Rhinos. Wolves. Pandas. Right? How about cabbage on a stick? Mead’s milkweed? Kuenzler hedgehog cactus? All of the above are endangered species, but while plants are less well known and less iconic, they are no less important and their reduced numbers affect biodiversity just as much as their zoological counterparts.
Botanist Kyle Wallick of the U.S. Botanical Gardens stated that the International Union for Conservation of Nature (IUCN) estimates that 40% of plant species are endangered as compared to 20-30% of vertebrates and an unknown number of invertebrates. This includes 941 species or about 5% which are federally listed. Wallick said that human land use has had the greatest impact on plant populations. However, he also noted that environmental and ecological events, such as geological movements, climate change, fire suppression in some cases, and catastrophic weather events like hurricanes and earthquakes can also affect plants. Habitat fragmentation and invasive species can also reduce plant populations.
In addition, a lack of pollinators can also affect plant diversity. Wallick gave the example of the Hawaiian plant cabbage on a stick (Brighamia insignia) and said it is not known what happened to the pollinator for this plant. It is native to two Hawaiian islands, Kauai and Niihau and largely grows on sea cliffs. According to Encyclopedia Britannica, the pollinator for this plant was a type of hawk moth which has since gone extinct. As a result, the plant largely exists in cultivation and is currently being pollinated by people.
Poaching can also impact threatened and endangered plants. Wallick said historically orchids, cacti, and other succulents are the most frequently poached plants, which puts pressure on wild populations. He did say he encourages growing endangered plants in gardens, so long as they have been legally purchased. He mentioned the Ben Franklin tree (Franklina alatamaha) which he said was “likely extinct” in the wild, but has been preserved in cultivation.
Wallick stressed the importance of education and knowing what plants in the area are threatened or endangered. He also suggested volunteering for invasive plant removal as invasives are a significant threat to native species.
While all endangered species, whether animal or plant are a threat to biodiversity, plants generally get less media attention and individual species of endangered plants are less well known. Nevertheless, many of them are still important to pollinators and are a vital part of the ecosystem. However, with education, preserving habitat, and limiting the spread of invasives, biodiversity can be restored to many parts of the globe.
Coming Next: My annual wildlife gardening article! This year I will feature a few endangered plants that can make great garden plants as well.