Key facts about Aizoaceae of South Africa
Family Overview
Aizoaceae, often called the fig-marigold or ice plant family, is a large group of dicotyledonous flowering plants in the order Caryophyllales. It encompasses around 135 genera and 1,800 species, with South Africa serving as a primary center of diversity for this family, particularly in its arid and semiarid regions.
Geographic Significance
South Africa is a global hotspot for Aizoaceae, hosting approximately 96% of its species—about 1,782 species across 132 genera—most of which are endemic. The Succulent Karoo biome, a renowned arid region, is especially rich in these plants, making it a critical area for their study and conservation.
Taxonomic Classification
The Aizoaceae family in South Africa is divided into five subfamilies: Aizooideae, Mesembryanthemoideae, Ruschioideae, Sesuvioideae, and Tetragonioideae. The Ruschioideae and Mesembryanthemoideae subfamilies stand out for their diversity, including well-known genera like Lithops (living stones) and Conophytum, which are iconic in succulent taxonomy.
Morphological Diversity
Aizoaceae plants exhibit remarkable variety, ranging from annual or perennial herbs to, less commonly, shrubs or small trees. Their growth forms are highly adapted to arid environments, with many species, such as the stone-mimicking Lithops, showcasing extreme succulence as a survival strategy.
Leaf Characteristics
Leaves in this family are typically simple, arranged oppositely or alternately, and succulent, with entire margins (rarely toothed). Their size varies significantly—tiny in some species like Brownanthus glareicola (3-5 mm) and larger in others like Brownanthus fraternus (up to 45 mm)—designed to store water efficiently in dry climates.
Stem Features
Stems of Aizoaceae are usually erect or prostrate, following a sympodial growth pattern. In succulent genera such as Brownanthus, they are articulated, green, and succulent when young, often becoming slightly woody with age. For instance, Brownanthus glareicola stems measure 3.5-5.5 mm in thickness.
Flower Structure
The flowers are actinomorphic (radially symmetrical) and typically bisexual, though some species are unisexual. They grow singly or in small cymes, featuring sepals (usually 5, ranging from 3-8) fused at the base. Notably, they lack true petals; instead, petal-like structures are often modified staminodes.
Flower Size and Shape
Flower dimensions and forms differ across genera. For example, Sesuvium portulacastrum produces narrowly trumpet-shaped flowers about 10-15 mm in diameter, while Lithops boasts larger, daisy-like blooms (up to 3-4 cm) in bright yellow or white, adding visual diversity to the family.
Ecological Adaptation
Many South African Aizoaceae, like Lithops, have evolved to mimic pebbles or rocks, with leaves fused into conical or spherical bodies—Conophytum, for instance, forms inversely conical structures 1-2 cm long. This camouflage aids survival in the harsh, arid climates they inhabit.
Succulent Karoo Hotspot
The Succulent Karoo, a biodiversity-rich arid region, supports over 60% of Aizoaceae species in South Africa. The Mesembryanthemoideae subfamily alone accounts for roughly 18% of the biome’s flora, contributing around 1,132 species to its ecological tapestry.
Taxonomic Challenges
The family’s hyperdiversity and relatively recent evolutionary origin pose ongoing taxonomic challenges. Generic and species boundaries remain fluid, with revisions common—for example, Lampranthus maximilianii was recently reassigned to Braunsia maximilianii based on updated classifications.
Photosynthetic Pathways
Aizoaceae species display varied photosynthetic strategies, including C4 and Crassulacean Acid Metabolism (CAM). CAM is particularly prevalent in genera like Mesembryanthemum, enabling these plants to conserve water by opening stomata at night in arid conditions.
Cultural and Economic Uses
In South Africa, species like Carpobrotus edulis (Hottentot fig) offer edible leaves and fruit, while Tetragonia tetragonoides (New Zealand spinach) is grown as a vegetable. Ornamental genera, such as Lithops, are also globally valued for their unique aesthetics.
Leaf Anatomy
Leaves of CAM-adapted Aizoaceae often lack distinct palisade and spongy parenchyma layers, featuring thickened, water-storing tissues instead. Epidermal bladder cells, as seen in Mesembryanthemum crystallinum, give a glistening appearance, inspiring the “ice plant” nickname.
Conservation Status
South Africa is home to 23,420 vascular plant species, with Aizoaceae prominently represented. However, 153 species, including some from this family, are threatened due to habitat loss and over-collection, particularly of ornamental varieties prized by collectors.
Additional Insight: Ethnomedicinal Importance
Certain Aizoaceae species hold traditional medicinal value in South African cultures. For example, Sceletium is chewed for its sedative effects, and Delosperma saturatum plays a role in Zulu rituals, though detailed documentation remains limited for lesser-known species.
Additional Insight: Invasive Potential
Native to South Africa, Carpobrotus edulis has become a global invasive species, particularly in coastal ecosystems. Its robust, trailing stems (up to 60 cm long) and large, showy flowers (3-4 cm petals) enable it to outcompete native vegetation in regions far beyond its origin.
