An attempt to understand more about this somewhat varied family of succulents.
Crassula alba, one of the more spectacular Crassulas found on Verloren Valei (Photograph: Steve Vincent)
Ten genera comprising 350 species of the Crassulaceae or Stonecrop family of herbs and shrublets are found across South Africa. The family includes Crassulas, Kalanchoes and Cotyledons. Many of them have the fleshy leaves of the typical succulent, helping them to thrive in different environmental conditions.
Crassula is derived from the Latin crassus,meaning “thick”, a reference to their succulent leaves.
This adaptability to extreme conditions is shown by the fact that several species of Crassula thrive on Verloren Valei’s high-altitude grasslands and wetlands. In this article, I will concentrate on the species of Crassula that are most common in the reserve.
Crassula alba
Crassula alba, showing its striking blooms — white in name only! (Photographs: Steve Vincent)
Crassula alba is an attractive succulent with a tuberous root system and erect flowering stems surrounded by dense rosulate leaves. It grows up to 500mm tall and produces tubular flowers that are usually red in Southern Africa (despite the fact that alba means “white” in Latin) with a few white flowers scattered in between. Apparently further north the flowers are predominantly white. The flowers can vary in colour from white to pink, red and sometimes yellow.
This species is native to the eastern half of Africa and is commonly found in rocky grassland and open deciduous woodlands from Ethiopia to South Africa. Flowering time is generally from January through April.
Crassula alba is traditionally used by the isiZulu people as a decoction to treat dysentery, diarrhea and heartburn. The sap mixed with water is used to treat influenza and other fevers. The Basotho people mix parts of the plant with tobacco to make a charm for a child born after the death of an older child, or as an ingredient in war charms to make one invisible or forgotten by enemies.
Crassula capitella ssp. nodulosa
C capitella ssp nodulosa (Photographs: Steve Vincent)
This plant’s name derives from the Latin capitella, having a small head, and nodulosa, having small nodes. The highly variable coloration of its leaves is influenced by environmental factors such as sunlight exposure, temperature, and growing conditions.
Typically, C capitella ssp. nodulosa has bright green leaves, sometimes with a hint of red on the tips and edges. The intensity of the red coloration depends on the abovementioned environmental factors; for example, the amount of sunlight to which the leaves are exposed.
The flowers are white to creamy in colour, very small, and urn-shaped. Flowering time is normally from December through March.
Crassula setulosa var. setulosa and var. deminuta
C. setulosa var setulosa (Photographs: Steve Vincent)
C. setulosa var. setulosa is a small (150-250mm tall) succulent shrub that grows primarily in dry biomes and on exposed quartzite, granite and sandstone ridges. This variety is characterized by its compact growth habit and delicate, hairy leaves (setulosa means “covered with small bristles). It is found along the south eastern parts of Africa, from Southern Malawi Mozambique, Zimbabwe, most of South Africa and Lesotho. Flowering time is usually December through to March.
C. setulosa var deminuta (Pigmy Cropstone or South African Pigmyweed) (Photographs: Steve Vincent)
C. setulosa var deminuta (meaning small – it stands 75-100mm high) is also known as a Pigmy Cropstone or South African Pigmyweed. It is a tiny succulent found in a few locations in the Steenkampsberg in Mpumalanga (where Verloren Valei is situated) and in northern Limpopo. Flowering time is usually December through March. It is listed as vulnerable in the 2009 Red Data Book.
Crassula vaginata
C. vaginata (Yellow Crassula or Yellow Stonecrop) (Photographs: Steve Vincent)
Commonly known as the Yellow Crassula, or Yellow Stonecrop, C. vaginata (i.e. having a sheath) is a rosette-forming succulent that can grow up to 500mm tall. It is characterised by its green to yellowish-green lance-shaped leaves, which may be hairy or smooth, and its star-shaped flowers. The sheath from which it derives its botanical name refers to the way in which the leaves envelop the stem.
C. vaginata, with the red arrows showing the sheath structure where the leaves meet the stem (Photograph: Steve Vincent)
This species is widespread in South Africa, including Mpumalanga, and thrives on damp grasslands and rocky slopes. Flowering time is normally from December through March. Flower colours vary from White to cream and yellow.
Its range extends from as far south as the Transkei northwards through tropical Africa and into Arabia. It seems as if its form and colour vary considerably throughout its range.
The roots of this plant are ground up by the Zulus and used with their amasi (sour milk)as a carbohydrate when meal is scarce. Parts of the plant have also been used to treat earache and bruises.
Crab spider (Thomisus species) lying in wait for a pollinator on C. vaginata (Photograph: Steve Vincent)
Many insects visit this flower looking for food. Crab Spiders often lurk amongst the foliage hoping to ambush a pollinator.
The as-yet-unnamed Crassula, possibly related to C. vaginata (Photographs: Steve Vincent)
A possible relative of C. vaginata exists, although it has not yet been formally named. It is a small, striking crassula, with red to green pointed leaves and a red unbranched stem. It stands +/- 100-150mm tall, has white flowers and is found in shallow quartzite soils at between 2000 and 2300m. It is fairly prolific at Verloren Valei, growing up on the ridges in shallow soils.
Crassulaceae Acid Metabolism (CAM) photosynthesis
CAM photosynthesis is an adaptation by various types of plant to enhance their chances of survival in arid conditions. It was first discovered in plants of the family Crassulaceae, but many plants, including 99% of Cactaceae, have been found to use this system of photosynthesis.
The discovery of CAM goes back to 1812 when a German botanist, Dr. Benjamin Heyne, observed the principles of acid exchange in a Crassulaceae plant leaf in India by tasting it at different times of the day. The name CAM photosynthesis was only coined in 1940.
Photosynthesis occurs in the presence of sunlight and carbon dioxide (CO2). The latter is taken into the plant via its leaf stomata, while moisture is also lost. CAM photosynthesis basically allows a plant to photosynthesize during the day, but to reduce moisture loss by obtaining its CO2 at night.
In a plant using full CAM photosynthesis, the stomata in the leaves remain shut during the day to reduce evaporation, but open at night to collect CO2, which diffuses into the cells. The CO2 is stored as malic acid at night; in the daytime, the acid is transported to chloroplasts where it is converted back to CO2, which is then used during photosynthesis. The pre-collected CO2 is concentrated around an enzyme, increasing the efficiency of the process of photosynthesis.
By allowing the plant’s leaf stomata to remain closed during the day, CAM photosynthesis allows plants to restrict the amount of water they lose, while still ensuring they receive the CO2 they need. It is thus most common in plants that live in arid environments, where water is scarce.
In the case of Verloren Valei, there are various factors that seem to indicate a more nuanced scenario. The reserve’s rainfall is highly seasonal, with the summer rains being fairly prolific and the winters largely dry and exceptionally cold and frosty. Most of the Crassula species that grow there die off during winter, and regenerate in spring from their bulbs, so CAM photosynthesis does not play a role in helping them survive the dry winter months.
Another factor is that CO2 is less available at higher altitudes, so CAM photosynthesis could also play a role in ensuring the plant has enough of it in high-altitude environments like Verloren Valei. The same principle apparently holds good for aquatic plants, which also use CAM photosynthesis to help overcome a relative shortage of CO2 in water.
However, much of the grassland vegetation of Verloren Valei is described as “sourveld”, which denotes predominantly well-drained soils. In addition, a feature of the geology is large quartzite outcrops which do not retain water well—the two variations of C. setulosa typically grow there. CAM photosynthesis could assist plants during the summer months during which dry conditions would prevail, despite the rains, due to the lack of water retention near the surface.
There is clearly much to learn about the Crassulas, and they stand as testimony to the incredible biodiversity of Verloren Valei and surrounding areas. Each species, with its distinct characteristics and adaptations, contributes to the rich tapestry of life in this area. By learning more about these remarkable succulents, we gain a deeper understanding of the natural beauty and ecological importance of Verloren Valei.
Author’s Note: I am a wildlife photographer and a naturalist at heart, and do not have any qualifications in botany or plant physiology. I have attempted to describe the complex processes of CAM photosynthesis in a way that is easy to understand, but in the process of simplifying them it’s possible I may have inadvertently misstated or misinterpreted the processes. If so, I apologise- the complex chemistry of CAM photosynthesis is fully described in the references below.
References
Wikipedia, https://www.wikipedia.org/wiki/crassulaceaen_acid_metabolism
iNaturalist, https://www.inaturalist.org/.
PlantZAfrica, https://pza.sanbi.org/.
Gerrit Germishuizen and Anita Fabian, Transvaal Wildflowers (Macmillian South Africa, 1982).
Braam van Wyke & Sasa Malan, Field Guide to the Wildflowers of the Highveld (2ed) (Struik, 1997).
John Manning, Photographic Guide to the Wildflowers of South Africa (Briza Publications, 2003).
Francis William Fox and Marion Emma Norwood Young (in collaboration with Desmond Hallowes, Rena Segal and Ruth Wustrow and botanical descriptions by Gerrit Germishuizen), Food from the Veld (3ed) (Delta Books 1988).
