Crassula fascicularis has pale coloured, evening-scented flowers, with long narrow corolla tubes, with the anthers inside the tubes, all of which indicate that it is pollinated by moths. This was confirmed by the 1993 study by Johnson et al., where no insect visitors were observed during the day, but light trapping at night caught a number of Geometrid moths with Crassula fascicularis pollen on their probosces. Thus Crassula fascicularis attracts and is pollinated by Geometrid moths. The flowers are fragrant from about midday and the fragrance grows stronger during the afternoon and into the evening, reaching a peak around midnight. The nectar is secreted in the afternoon until midnight, while the moths are active. The volume of nectar and the intensity of the fragrance are at their peak just before midnight.

Crassulas have an extraordinary metabolism that allows them to photosynthesise normally without losing much water through their leaves, known as Crassulacean Acid Metabolism or CAM. This gives them the ability to survive and thrive in dry regions or those that experience recurring droughts. All plants need CO2 (carbon dioxide) for photosynthesis. Most plants take in CO2 during daylight hours through their stomata (pores in the leaves) and cannot avoid losing water at the same time through these open pores. In Crassula the stomata are closed during the day, but open at night, so that when they take in the CO2, they lose the least amount of water. The CO2  taken in at night is stored in the form of organic crassulacean acids. During the day, these acids are broken down and the CO2  is released and re-used in the photosynthetic process. In this way they lose much less water, yet can photosynthesise normally during the daylight hours. Furthermore, during extremely dry periods they won't even open their stomata at night, and will re-cycle the CO2 within the cells. They would not be able to grow at all, but the cells will be kept healthy – this is known as CAM-idling.

Most crassulas have hydathodes on the leaves. In Crassula fascicularis they are in a dense row along the upper and lower leaf margins, but they are very small and usually hardly visible. Hydathodes are special water-secreting structures on the surface of a leaf, similar to stomata, but larger. They are mostly found on aquatic plants where their function is to get rid of excess water in the plant. In Crassula, which are adapted to arid environments, the hydathodes have a different function, they are able to take up liquid water on the leaves. This enables them to survive in arid regions where rainfall is infrequent but the plants often get wet from dew or fog.