In general, the steeper and rougher the terrain you plan to cross, the heavier and stiffer boots you need.  Most people need a mountaineering boot with a stiff shank, heel counters and stiff leather upper to help them handle steep and rocky off-trail hiking.  Mountaineering boots are designed to protect your feet and ankles, and to stabilize your foot and prevent sliding off steep slopes.   Mountaineering boots are expensive, hot, hard to break in, and heavy, but if you're planning to do field work in rough areas, carrying a backpack, they are a necessary evil.  If you are wearing more boot than you need, your feet might get hot or you might get a blister.  If you are wearing less boot than you need, you might take a slide down a steep and rocky slope, injuring a knee or an ankle.  (Boots are not as expensive as field time lost to injuries, or trips to the emergency room).  You can buy boots at most outdoor stores.   Make sure the boots you buy fit well, and  check to make sure your toes don't bang into the front end when walking downhill.

Light weight boots or running shoes are fine if you're not climbing steep slopes, or if you plan on staying on a trail, and not picking up many specimens.  Unfortunately, it is remarkably easy to pick up twenty or thirty pounds of rock.  However, wearing a pair of gaiters (typically intended to keep snow out of your shoes) over your light weight shoes will generally take care of this problem.