Plant theory: what's the difference between indigenous plants and endemic plants?

Here's the first in a new series on plant theory aka botany. A first in more ways than one for me, as I'm not in the least a botanist myself! But teaching is a good way to learn, right? It was inspired by Clarissa from Oakey Creek Bushcare, who asked the question this post is aiming to answer. What's the difference between an indigenous plant and an endemic plant? 

Many people are unsure of the difference, and quite reasonably so. Both terms are thrown around freely and not always defined. It's easy to get confused. So here's my attempt to explain the difference. 

An indigenous plant is native to a given area, meaning it grows there naturally and hasn't been introduced (recently) by humans. In Illawarra, there are upwards of 1,000 indigenous species, depending on how you define the area. Indigenous species in this area include the usual suspects such as the Illawarra Flame Tree (Brachychiton acerifolius), Illawarra Plum Pine (Podocarpus elatus) and less well-known species such as the Illawarra Irene (Irenepharsus trypherus) and Illawarra Socketwood (Daphnandra johnsonii). 

Illawarra Flame Tree captured by Tracee Lea (c). 

An endemic plant has a tighter definition. It is a species that is native to a given area, and that only grows naturally in that area. So, if we take the four indigenous species mentioned above, only two of them are endemic to the Illawarra region. Illawarra Flame Tree and Illawarra Plum Pine grow naturally in this region but also occur naturally outside of it. The other two species only grow naturally in the Illawarra region, and are therefore considered endemic to the region. 

Illawarra Socketwood leaves, photographed by Phill Bragg. The Illawarra Socketwood is one of a few species that are endemic to this region. 

That's the difference in a nutshell. Indigenous = grows naturally in an area. Endemic = grows naturally in an area and nowhere else. 

There are of course lots of riders and qualifications to this general rule; it gets really complex if you think about the issues hard enough. Plants' natural distributions change over time without human intervention, as species extend or decrease their natural range as a result of climatic and other pressures, or spread by vectors (carriers) such as birds, bats and insects. And human intervention changes plants' distributions in ways that it may be difficult to classify as either 'natural' or 'unnatural.' Plant theory may sound like it's all about botany, but we encounter philosophy before too long! 

Either way, enjoy your indigenous and endemic plants!