Looks to me like the smooth texture has psyllium husk as the fiber source, and the clear and natural has inulin. The website says the inulin comes from chicory roots.
The text below is directly copied and pasted from Metamucil's website.
If you're looking for an easy, flavor-free way to add fiber to most of your favorite beverages and foods, Metamucil Clear & Natural is for you. The 100% natural inulin fiber in Metamucil Clear & Natural is perfect for those who want to add more fiber to their diet, and don't want to add extra flavor or taste.
Found in Metamucil powders, capsules, and wafers, psyllium fiber is a great option for those looking to take fiber to get multiple health benefits** from their fiber supplement, such as helping to lower cholesterol*** and promoting the natural cleansing process†. If you like your fiber to have a great flavor, try the tasty and healthy Metamucil psyllium fiber products.
Status: Remission since late May 2009!
Symptoms began in November 2008, ~4 weeks after giving birth to my son.
Diagnosed with pancolitis on 1/30/09
Currently taking Apriso (4 pills ONCE!! daily), Rowasa twice weekly, Natural Factors Ultimate probiotic 12/12 Formula, and Zoloft (25 mg).