Crassulaceae
Crassulaceae J.St.-Hil. comprises approximately 34–36 genera and 1,400–1,500 species, occurring predominantly in temperate and subtropical regions of the Northern Hemisphere, southern Africa, and Mexico. Molecular phylogenetic studies have refined the classification of several genera, particularly Sedum, Sempervivum, Aeonium, and Kalanchoe, while confirming the family's monophyly. Crassulaceae is distinguished by its succulent leaves, free carpels, follicular fruits, and the widespread occurrence of Crassulacean Acid Metabolism (CAM) photosynthesis.
Key characteristics
- Annual or perennial succulent herbs or subshrubs
- Leaves thick, fleshy, simple, and exstipulate
- Leaves often arranged in rosettes
- Flowers actinomorphic, usually pentamerous
- Carpels free (apocarpous)
- Superior ovary
- Fruit composed of several follicles
- CAM photosynthesis common
Distribution
Crassulaceae is widely distributed in Europe, Asia, Africa, North America, and Mexico, with major centres of diversity in southern Africa, the Mediterranean region, Central Asia, and Mexico. Members commonly inhabit rocky cliffs, alpine meadows, dry slopes, deserts, scree fields, forest margins, and other xeric habitats where water availability is limited. The family is primarily distributed in the Himalayan, Karakoram, and Hindu Kush mountain systems, extending into the western dry mountains, Salt Range, and Potohar Plateau. Species occur on rocky slopes, alpine meadows, cliffs, limestone outcrops, and dry mountain valleys. Several ornamental species are cultivated in gardens, botanical collections, and rock gardens throughout Pakistan.