Didiereaceae
Didiereaceae is a family of flowering plants found in continental Africa and Madagascar.
It contains 20 species classified in three subfamilies and six genera. Species of the family are succulent plants, growing in sub-arid to arid habitats. Several are known as ornamental plants in specialist succulent collections. The subfamily Didiereoideae is endemic to the southwest of Madagascar, where the species are characteristic elements of the spiny thickets.
Systematics
The family was long considered entirely endemic to Madagascar until the genera Calyptrotheca, Ceraria, and Portulacaria from the African mainland were included. Molecular phylogenetic analysis confirmed the monophyly of the family and its three subfamilies:The family is closely related to the New World family Cactaceae, sufficiently closely so that species of Didiereaceae can be grafted successfully on some cacti.
Calyptrothecoideae
Contains only one genus, Calyptrotheca, with two species found in tropical East Africa.Didiereoideae
This subfamily is endemic to Madagascar, where it is found in the spiny thickets of the dry southwest. The plants are spiny succulent shrubs and trees from 2–20 m tall, with thick water-storing stems and leaves that are deciduous in the long dry season. Some species build a distinct youth form as small procumbent shrubs before a dominant stem is produced. All species are dioecious. The leaves, produced from the brachyblasts, are small, appear single or in pairs and are accompanied by conical spines. The flowers are unisexual and radially symmetric.There are four genera with eleven species:
Alluaudia
- Alluaudia ascendens
- Alluaudia comosa
- Alluaudia dumosa
- Alluaudia humbertii
- Alluaudia montagnacii – probably a natural hybrid of A. ascendens and A. procera
- Alluaudia procera – quite easy grown and the most frequent species in cultivation
- Alluaudiopsis fiherensis
- Alluaudiopsis marnieriana
- Decarya madagascariensis
- Didierea madagascariensis
- Didierea trollii
| 1 | Spines in groups of four or more: | Didierea |
| - | Spines single or in pairs: | → 2 |
| 2 | Shoots striking zigzagged, spines short conical: | Decarya |
| - | Shoots not zigzagged, spines long conical to needle-like: | → 3 |
| 3 | Shrubs strongly branched, leaves lanceolate: | Alluaudiopsis |
| - | Shrubs little branched, leaves either ovate to circular or scale-like and awl-shaped: | Alluaudia |