South Africa’s allergenic plants
Wind versus insect pollen and its impact on allergies
1. Not all plant pollen causes allergy
Pollen that triggers allergic symptoms is called “allergenic”. Not all pollen is allergenic.
Big bright flowers like those from jacaranda or acacia trees, which are large, sticky and insect pollinated are NOT allergenic.
Windborne pollens are mostly allergenic. They usually come from small, insignificant plants like grasses. Grasses release millions of windborne pollen grains in spring.
The most allergenic pollen in SA comes from the plants that are not indigenous but have been introduced; for example trees like plane and oak from the Northern Hemisphere are extremely allergenic.
Fynbos is rarely allergenic
2. South Africa's most allergenic Plants
Cypress trees were introduced from Europe. The African species is Widdringtonia from the Cedarberg area. These evergreen trees produce woody cones and release their allergenic pollen from June.
Quercus robur is the species of oak tree most commonly found in South Africa. Oak trees produce acorns from late summer then shed their leaves. Allergenic pollen is released in spring.
The wild olive Olea europaea, subspecies Africana is a popular tree that has been planted throughout South Africa especially in public spaces. It releases allergenic pollen from October to March.
This indigenous tree is widely planted because it is fast-growing and economical with space. There are 74 species with diverse flowering times, so the allergenic pollen is released from October to March. Although it is insect-pollinated, the pollen is detected in air samples. The sap from this tree may cause contact dermatitis.
This tiny grass flowers in June in winter rainfall areas. It is related to Poa pratensis or Kentucky blue grass, and has characteristic crinkled ‘herring bone’ pattern on some of its leaves.
Avena fatua/A. barbata
Wild oat grass appears in midwinter in some areas, but takes a few weeks to grow to its maximum height of 1-4 feet before it releases pollen. It produces long waving fronds from August.
Thatching grass is very tall and widespread in South Africa, but is mostly found in the grassland areas of Gauteng and the Eastern Cape, and releases pollen from September to June.
Bermuda grass must be tested separately when patients undergo grass sensitivity tests because it does not cross-react as most other grasses do. It grows most happily in sandy soil and releases most pollen in late summer but it may be seen throughout the year.
This indigenous African grass is known as buffalo grass and is a coastal grass. It may be seen in the Cape, especially along the east coast and on the Otter Trail between Knysna and Nature’s Valley.
The common name for this grass is Kikuyu and it originated in East Africa. It is favoured as a lawn grass. Take care that the nursery is selling the female grass seedlings that do not produce pollen. Like bermuda grass, kikuyu grass allergy must be tested for separately.
There are numerous species of reeds and they are found throughout South Africa. They are happiest growing close to water in rivers or lakes. The different species flower at different times of the year, so that there is Restio pollen in the air all year round.
There are many species in the Asteraceae family – Spring daisies and Cosmos – and there are few months without cheerful daisies. November and March are the peak months for Cosmos.
3. Mould allergy
Mould allergy may trigger asthma or allergic rhinitis. Most of the fungal spore or mould aeroallergens fall into 3 phyla, or divisions: the Zygomycota, Ascomycota and the Basidiomycota. Moulds commonly grow on decaying vegetation, compost heaps and soggy autumn leaves, but provided the conditions for their growth are met they will grow indoors and outdoors. Common allergenic moulds are Alternaria, Aspergillus, Cladosporium, Epicoccum and Penicillium. The different moulds may have a wide temperature range and while some are ‘dry air’ moulds, others prefer moist environments. However, even the ‘dry air’ moulds require some moisture for their growth. Rain, followed by warm temperatures favours high concentrations of airborne mould spores. Unlike plants, moulds will produce spores in any season provided the weather conditions are suitable.
Autumn and spring often provide ideal conditions in the Western Cape, while many moulds will flourish for much longer periods in the subtropical climate of KwaZulu-Natal. In Mpumalanga moulds grow best in the warm, wet summer months.