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.

Interesting facts

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

Most fynbos plants have pollen that is pollinated by insects, birds or small mammals like mice or bats. The pollen is not easily airborne and is not wind blown like grass and so is not as easily inhaled.

2. South Africa's most allergenic Plants

Trees

Cypress-Tree

Cypress trees

Cupressaceae

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.

Oak-Tree

Oak trees

Quercus robur

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.

London-Plane

Plane trees

Platanus acerifolia

Plane trees, most commonly London plane trees, have a short pollen-release season of six weeks in spring when they flower from the end of August.

olive tree Olea-europaea-africana

Olive trees

Olea europaea

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.

Elm-Tree

Elm trees

Celtis Africana

Celtis Africana or white stinkwood is an indigenous South African hardwood tree that flowers from October to March releasing allergenic pollen.

Rhus

Rhus

Searsia

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.

Grasses

Ryegrass

Ryegrass

Lolium perenne/L. temulentum

Ryegrass is considered to be extremely allergenic. It flowers in mid-season, from late September.

Poa-Annua

Winter grass

Poa annua

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.

Wild-Oat

Wild oat grass

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.

Bunny-Tail

Bunny tail grass

Lagurus ovatus

‘Bunny tail grass’ appears in September-October. It is found in sandy soil but is rarely seen in the heavier soil of the land close to the mountains in the Cape.

Thatch-Grass

Thatching grass

Hyparrhenia hirta

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

Bermuda grass

Cynodon dactylon

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.

Buffalo-Grass

Buffalo grass

Stenotaphrum secundatum

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.

Kikuyu

Kikuyu

Pennisetum clandestinum

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.

Weeds

English-Plantain

English Plantain

Plantago lanceolata

This weed is widespread throughout South Africa and is seen during most months of the year, although its peak flowering season is in December.

dandelion-taraxacum officinale

Dandelion

Taraxacum officinale

The dandelion flowers more strongly in summer but it appears throughout the year. Its peak flowering time is late summer-autumn.

Reeds-Restionaceae

Reeds

Restionaceae

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.

Daisies-Cosmos

Daisies/Cosmos

Asteraceae

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.

erica-heath

Heath

Erica

Heath are Fynbos plants in the genus Erica. Fynbos are mostly insect-pollinated, but pollen from species of this genus is constantly found from air samples from July until March.

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.

Alternaria
Alternaria
Cladosporium
Cladosporium
Epicoccum
Epicoccum
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