Diversity:  A family of 25 genera and over 900 species of  annual and perennial (mostly) herbs and some shrubs.  Mostly xerophytes that sequester water in the leaves producing a fleshy leaf succulence, manifested by many 'rock garden' taxa in this family.  Many genera also show an unusual (present in about 5% of the flowering plant species - ca. 18 families) physiological feature, "Crassulacean acid metabolism (CAM)", that allows gas exchange (CO₂ acquisition and conversion to organic acids) to occur at night, via open stomata (pores in the leaves) and, during the day when the stomata are closed, the CO₂  released and used immediately in photosynthesis. As a result, the plant is able to conserve water.

Distribution:  World wide, but most diverse in southern Africa - we have 5 genera witrh 11 species in Texas.

Floral structure:

 Significant features:  Vegetative characters include fleshy, succulent leaves that often show a three-dimensional (as opposed to laminar) form, either opposite or alternate.  Generic variation with regard to perianth part numbers and connation; stamens usually twice the number of perianth parts, and the gynoecium usually apocarpous (some basal fusion) with each carpel subtended by a nectar-producing scale and the fruit a follicle.  (image from Delta)
 

  Sedum nuttallianum  - rare local (sandy areas) of the largest Genus.

Sedum nuttallianum - succulent leaves, sepals - and apocarpy
 
 

4-merous, connate flower (left) and inflorescence (right - UH Botany) of Kalanchoe

More information on the Crassulaceae