To someone from the Great Lakes region, botanizing in Florida in March can be a bit difficult. It seems like nearly all of the trees have entire-margined, thick-textured, glossy green ovate leaves. Similarly, many of the palms (Arecaceae) look very similar; specifially, the palmettos (Serenoa, Sabal), with palmate to costapalmate leaf blades, look nearly identical at first glance. Below, I will summarize the differences between the species in this latter group that occur in Florida.
Serenoa repens (Saw Palmetto) tends to have leaf blades that are yellowish-green (see photograph above), whereas the leaves of Sabal palmetto (Cabbage Palmetto) are more blue-green (see photograph below). In addition, Serenoa repens has a shrubby growth form; Sabal palmetto usually becomes a tree, though it sometimes has no aboveground trunk.
Looking at the leaves up-close, it is even easier to distinguish between Serenoa repens and Sabal palmetto.
In Serenoa repens (above), the petiole has serrate margins (that will cut through your skin, trust me), thus the common name Saw Palmetto. The petioles of Sabal palmetto are entire. Also, take a look at the apex of the leaf rachis. In Serenoa repens, the apex is blunt, whereas in Sabal palmetto, the rachis is spear shaped.
Serenoa repens grows in pine woodlands, scrub, and mesic hammocks; Sabal palmetto, Florida's state tree, can be found in pine woodlands, hammocks, and on river banks. The two are sometimes found growing together, as seen below.
That takes care of the two most common Florida palmettos. The other two, both in the genus Sabal, also have petioles without serrate margins.
Sabal minor (Dwarf Palmetto) can look similar to Sabal palmetto, but as its common name suggests it is a much shorter plant. Found in moist soils and wetlands, the trunk of Sabal minor typically remains underground. In addition, the fruits of Sabal minor are a bit smaller than those of Sabal palmetto.
Sabal etonia (Scrub Palmetto), a Florida endemic, is found in dry, sandy soils in scrub habitat. Its leaves are smaller and have narrower segments than either Sabal palmetto or Sabal minor. Like Sabal minor, the trunk is subterranean, so Sabal etonia doesn't grow more than 3-6' tall.
That should do it. Should you find yourself in the midst of Florida palmettos, hopefully this summary will help you to determine which species you are seeing.