This looks more like portulacaria afra, often called (mistakenly) mini-jade, rather than a crassula, but their care is similar. this plant has very few leaves, so let me ask some questions to get an idea about its health. What kind of soil is it potted in, how much sun does it get, and if you feel the base of the trunk with your fingers are there any soft spots underneath the bark?

Gill has it right most likely - the plants are heavily fertilized by growers before sold, and accumulation of salts from fertilizer is very likely. And gentle brushing as she suggested would get rid of some loose & dry flakes. Then do the 'squeeze test' - gently squeeze the trunk, it should be firm. If soft, there may be some rot (I don't think that's the case). Do you want to keep it 'small' as bonsai should be? - it is slightly different growing, methods to restrict the growth and keeping plant compact would be necessary. Thick trunk & gnarled branches make it look like an old tree.

Madalyn - you look very young in your picture and you express yourself very well for someone so youthful. ;-) Even in FL, plants go through an annual growth cycle. During this cycle, the plant's level of vitality and growth rate waxes and wanes. The best time to do serious work on a plant, like full repots and hard pruning, is when the plant's potential for making food and its stored energy reserves are highest. In human terms, it might be like an athlete planning his training so he reaches peak performance when his biggest contests are scheduled. For plants, the longest, brightest days are usually in June, so the best time for me (in Michigan) to repot P afra is in June - around Father's day. For you, it would be a few weeks earlier due to how much further south you are. The pruning isn't necessary for the plant's health. Actually, pruning always robs a plant of potential growth and vitality, but I'm one of those people who are unwilling to sacrifice appearance on that altar. IOW, I'm willing to let a plant look temporarily unkempt if I have a good reason, but if there is no reason, I'll gladly sacrifice some of that growth potential and vitality in the immediate for long term good looks. I don't think anyone understands that concept better than a bonsai practitioner. We don't consider existing plant mass sacred. We'll gladly sacrifice limbs and bend branches and trunks to produce something that's pleasing to the eye, rather than something that jars the eye because the eye knows 'something's wrong'. Often, we can't even express/describe what we know is out of place, we just know it is. Fortunately, it's not that difficult to keep your plant healthy AND looking good. Working on your plant when it's in the strong part of the growth cycle and avoiding subjecting it to unnecessary stress when it would rather just be left alone (Sep thru May), are sound strategies that put you in sync with the plant, which makes the plant's life easier. Make sense? Let's change places - I'm you and you are me. I would check to see how crowded the roots are - just to satisfy my curiosity, and post a picture of the roots. It will lift right out of the pot with little fuss. Then, the next time the plant needs water, I'd flush the soil thoroughly to get rid of any accumulation of mineral salts in the soil. Then, I would fertilize with an appropriate fertilizer at recommended strength. Following that, I would start checking the soil moisture level with a wooden dowel rod sharpened in a pencil sharpener. It gets stuck all the way to the bottom of the pot and pulled out after a few seconds. If it's moist or stained dark by the soil - withhold water. If it's dry - water. In early June, around Memorial day or a week later, I would do a full repot into a soil you know you can water to beyond saturation w/o having to worry about the soil staying wet so long it wrecks root health or function. That last part is a whole conversation in itself, but I'll wait to hear your thoughts before I elaborate - if you're even interested. This P afra bonsai was getting too heavy (branches too thick) near the top, so I cut it back hard and am in the process of reworking the top of the tree. It will look pretty ugly for a while (see below), but it's a sacrifice I had to make in order to improve the tree. It will take 3 years to restore the tree to something that has some eye appeal. Al

http://homeguides.sfgate.com/cure-root-rot-jade-39826.html In my opinion and this is what I'd do but you don't have to. Id re pot it... Serialise soil mix in microwave.. Check roots and the bottom. I'd cut the top half off the top of the jade. And inspect.. Sterilise the knife before cutting with alcohol and you can use a antibacterial gel on the stem once cut. Take it outside so it gets some light. Use se the top cutting once it's healed to make another jade plant.