Number five in the series on South African plants and biomes series from Taisha, who writes:
The informally-recognized thicket biome of South Africa is featured today with an accompanying photograph of Crassula ovata. This image is another shared via the Botany Photo of the Day Flickr Pool, and photographed by Sean Rangel@Flickr. Thanks for sharing, Sean!
The Albany thicket occurs along the Fish, Sundays, and Gamtoos river valleys in the eastern Cape, and moves west along the intermontane valleys of inland Fold Mountains and east into Maputaland-Pondoland Bushland and thicket. Annual temperatures range from 0°C to 40°C, with it being more extreme inland, and more moderate toward the coast. Annual rainfall is between 300-550mm per year, varying between inland and coastal areas, and valley mists are common on the coast. Soils are deep, lime-rich, sandy loams that are well drained and often have low moisture levels for extended periods of time.
The Albany thicket can be divided into three regions, each with unique vegetation patterns. The dry, inland areas of the Fish, Sundays, and Gamtoos Rivers are rather sparse, and have been classified as Valley Bushveld. This region contains both leaf and stem-succulent shrubs and a few characteristic woody species. Coastal area of these river valleys, known as Kaffarian succulent thicket, are extremely dense with ~90% canopy cover. These thickets are rich with species of spinescent shrubs, woody vines and succulents. Lastly, the intermontane valleys, know as Spekboomveld or Spekboom succulent thickets, are a dense shrubland dominated by Spekboom (Portulacaria afra) with other succulents, herbs, and grasses also occurring.
Crassula ovata is one of the most common crassulas occurring in South Africa. This well-branched succulent shrub occurs naturally on rocky hillsides from Willomore to East London, and north to Queenstown and KwaZulu-Natal. From a picture of the foliage, you may recognize that this as the commonly cultivated plant known as the jade plant or money tree. Many people grow these as container plants, both in and outdoors.
Like most Crassula species, Crassula ovata reduces water loss from its leaves by utilizing Crassulacean Acid Metabolism, or CAM. Part of the CAM biological process is that stomata are closed during the day to prevent water from evaporating, and instead opened at night to collect carbon dioxide (this is the reverse of how most plant species exchange gases, with stomata open during the day instead). The carbon dioxide is stored overnight in the form of crassulacean acids, which are then broken down during the day. This releases the CO2 for the photosynthesis process during the day. During extremely dry periods, Crassula species may undergo CAM-idling, where stomata are not opened during the day or night. Instead, the plants will recycle the CO2 within the cells. This leaves them unable to grow or develop new tissue, but the plants are able to survive the lack of water by losing very little of it during this time.