Christmas Cacti are houseplants that are known for blooming around the holiday they are named after. They are usually placed outdoors during the summer and, unlike most cacti, they prefer light shade and temperatures between 70- and 80-degrees F. When brought in for the fall and winter they rely on shorter days and cooler temperatures to bloom.

Most complaints about Christmas cacti are that they do not bloom or drop their blooms. The dark and withered branches on your cactus is most likely caused by a watering problem. The soil, during the winter, should not be allowed to become too wet. Allow the soil to just dry out to the touch before watering again. Too much water can cause wilting and lose their color.

Too much water can also cause fungal disease which will rot the roots of your plant. It is hard to tell from your picture if that is what is affecting your Christmas cactus. To look at the roots, dig into the soil and look at the roots. If they are dark and appear to be disintegrating, you most likely have a fungal root rot. This may eventually cause the plant to die. If you believe your Christmas may have a root rot, it might be good to start new plants by removing some of the stem sections and plant them in potting soil.

For more information: Holiday Cacti.