Specific details go a long way. A character who researches non-flowering plants has more credibility than one who is simply labeled a botanist. Including the names of things can also help make her believable. Someone who can identify smooth rock tripe certainly has some specialized knowledge. If she keeps an eye out for liverworts wherever she travels in order to take a photo of every sighting, it will be clear she has a passion for her work.
]Still, your concern is a valid one. While these details are certainly crucial, you don’t want your character to pass muster only on the surface. In order to make her seem like a living, breathing individual with a history, you need your character to view the world—of plants and non-plants—through the perspective of someone with this kind of knowledge. You can do this without a botany degree, but it will take a bit of investigation.
Narrow your focus as much as possible. You don’t need to tackle the entire field of botany, or even that of non-flowering plants. Perhaps she’s interested in woodland plants, specifically a type that uses camouflage to hide from predators. (You can do this narrowing with any occupation. An optometrist could work at a vision center at a strip mall, have her own private practice, teach at a university, or work specifically with those who have experienced head trauma.) This focus will help direct your research.
Gather as much information as you can on the specialized topic. Find images in field guides, visual dictionaries, and Internet searches. Seek out first person accounts. Read memoirs, essays, and articles. Conduct interviews. You may only use a small amount of the specific information you gather as detail in the story, but this whole body of knowledge will help inform your characterization on a deeper level.
Of course, you’ll be inventing, too. This is fiction, after all, and you’ll need to imagine your way into your character’s perspective. This investigation will give you a solid foundation. You’ll have a firm grasp on how her occupation might influence her thought process and a wider scope from which to draw references.
There’s no reason to limit yourself and stay within the strict boundaries of what you already know when creating characters. Karl Iagnemma wrote “The Phrenologist’s Dream” from the perspective of a phrenologist, a person who studies skulls to determine personality. Phrenology is a defunct study now, but that didn’t stop Iagnemma from bringing this character to life. Plenty of authors dabble in characterization outside their own experience. If the story demands it, go find it.