I think it depends on what you actually mean.
"I found a plant that I couldn’t immediately identify." (yes, you have to recognise a species first in order to identify it. Moreover, when you identify a plant, you are recalling its scientific name, order, rank, family and so on.)
"I found a plant that I couldn't immediately recognise." (you recognise a plant by looking at certain physical characteristics and recalling from a list of plants that you already know. There has to be some prior knowledge of that thing. You can recognise a primary school classmate, but you cannot recognise a stranger.)
You RECOGNISE a plant by looking at its bulbous stem and needle-like leaves (all these are characteristics). And because you have seen pictures of cacti in a gardening magazine before (prior knowledge), you search the Internet, narrow down your search and managed to IDENTIFY it as an Opuntia (prickly pear).