Hay fever plants and Weather

Plant species producing allergenic pollen

Hay fever is only provoked by airborne pollen, sometimes by amphiphilous species (in with pollination occurs by the wind, as well as by insects). It is a luck that only little types ofpollen are allergenic among entomophilous plants (with wind pollination) which produce large amounts of airborn pollen (see tables here below about allergenic pollen). The risk to be in contact with pollen transfered by insects (entomophilous), like that of most garden plants with colorful flowers, is low, and besides this pollen is known to be little allergenic. Some species which in first instance are suspicious because they release remarkable amounts of pollen in the air do not (or seldomly) cause hay fever (Examples: the Ash, Aspen and Taxus, resp. Fraxinus excelsior, Populus sp. and Taxus baccata, see video presentations of the Ash, Aspen and Taxus, and illustrated descriptions of Ashes, Aspens, Taxus species and a SEM photo of Taxus pollen). Although this is the general tendency, some people are yet sensitive to pollen that is known as little or not allergenic. And opposite, the great majority of the population does not suffer of hay fever.

In the Netherlands and Belgium the pollen of the following plant species is most responsible for hay fever symptoms (upper table, groups arranged according to their allergenicity / importance; lower table with links to video's, descriptions and scanning electron microscopy photo's of the plants. Take care, realize that this list is not complete and take into account individual differences in specific sensitivity and (cross-)reactions). In South-European countries, in top of the grasses, Pellitory-of-the-wall, Eastern Pellitory-of-the-wall and Olive are the main source of hayfever pollen (see video "Vakantiepollen" showing these plants in details on pollennieuws).

The weather

[eng] The weather is a main factor for the formation and dispersal of pollen. Temperature, air humidity and precipitation not only have a great influence on the flowering time of plants, but also on the duration of the blooming and on the amount of flowers and pollen which are produced. For hay fever patients dry and sunny weather is most unfavorable, because then the anthers disrupt and pollen is shed in mass. If in addition the wind is blowing, pollen can be dispersed over long distances. This is not the case with rain weather which also helps to wash much pollen away. The weather forecast is an important consideration in making hayfever predictions (to the site of the KNMI)

Main sources of hayfever in the Netherlands and Belgium
	Grasses (Grass family = Poaceae or Gramineae; e.g. Cockfoot pollen, one of the major source of hay fever (May-fall).
	Birches (i.e. the Silver and the Downy Birch, which flower in spring. Photo: Birch pollen
	Mugwort which flowers in summer. Photo: Mugwort pollen
	Alders, e.g. the Common and the Grey Alder, causing both hay fever already in wintertime. Photo: Alder pollen
	Hazel, which flowers early in the year. Photo: Hazel pollen
	Plantains, which flower from May to September. Photo: Ribwort Plantain pollen
	Sorrels (Dock species) which flower most in May and June, but even until October. Photo: Sorrel pollen
Level of allergenicity and occurance of disconfort from low / seldom (0-1) to high / common (4-5)
Note 1: Allergenicity = how seriously causing hayfever) Note 2: Alders and Hazels belong both to the Birch family or betulaceae. Most people become allergic for Alders and Hazels pollen only when they are already allergic for Birch pollen. This is also valid for Oak pollen. More about cross-reactions at natuurkalender.nl Note 2: In southern countries hayfeverisalsocaused by other plants like olive trees and cypresses.

Click in the table here below on the arrows ↑ ↓ to sort according to the alphabetical order, level of allergenicity or month

Plant species with allergenic pollen
Scientific name Alphabetically ↑ ↓	English name Alphabetically ↑ ↓	Allergenicity 0-5 Sort ↑ ↓	Flowering month(es) Sort ↑ ↓	Tree/ Bush Grass Weed Sort ↑ ↓	Video ⁽¹⁾ Flora ⁽²⁾ (Links)
Alnus glutinosa Alnus incana	Common Alder Gray Alder	3	02-03-04	Tree/ Bush	Wild plants
Alopecurus pratensis	Meadow Foxtail	5	04-05-06-08-09	Grass	Wild plants
Ambrosia sp.	Ragweed	5	08-09-10	Weed	Wild plants
Anthoxatum odoratum	Sweet Vernal Grass	3	04-05-06	Grass	Wild plants
Arrhenatherum elatius	False Oat-grass	5	05-06-07-08-09	Grass	Wild plants
Artemisia vulgaris	Mugwort	4	06-07-08-09	Weed	Wild plants
Betula sp.	Birch	4	04-05	Tree/ Bush	Wild plants
Bromus hordeaceus	Soft Brome	5	05-06-07	Grass	Wild plants
Carpinus betulus	Hornbeam	0 1	04-05	Tree/ Bush	Wild plants
Cedrus sp.	Cedar	4	08	Tree/ Bush	Wiki
Corylus avellana	Hazel	3	01-02-03-04	Tree/ Bush	Wild plants
Cynosurus cristatus	Crested dog's-tail	5	06-07-08-09-10	Grass	Wild plants
Dactylus glomerata	Cocksfoot	5	04-05-06-07	Grass	Wild plants
Elytrigia repens	Quackgrass	5	06-07-08	Grass	Wild plants
Holcus lanatus	Yorkshire-fog	5	05-06-07-08	Grass	Wild plants
Holcus mollis	Creeping Soft Grass	5	06-07-08	Grass	Wild plants
Lolium multiflorum	Italian Rye Grass	5	06-07-08-09-10	Gras	Wild plants
Lolium perenne	Perennial Ryegrass	5	06-07-08-09	Grass	Wild plants
Parietaria judaica	Pellitory-of-the-wall	5	05-06-07-08-09-10	Weed	Wild plants
Parietaria officinalis	Eastern Pellitory-of-the-wall	5	06-07-08-09-10	Weed	Wild plants
Phleum sp.	Timothy	5	06-07-08	Grass	Wild plants
Plantago lanceolata	Ribwort Plantain	2	05-06-07-08-09	Weed	Wild plants
Poa annua	Annual Meadow-grass	5	04-05-06-07-08-09-10	Grass	Wild plants
Poa pratensis	Smooth Meadow-grass	5	05-06-07	Grass	Wild plants
Quercus robur Quercus petraea	Pedunculate and Sessile Oak	0 1 variable	04-05	Tree/ Bush	Sessile Oak Pedunculate Oak wilde-planten.nl
Rumex acetosa Rumex acetosella Rumex crispus Rumex obtusifolius	Common Sorrel Sheep's Sorrel Curly Dock Broad-leaved Dock	1	05-06	Weed	Common Sorrel Sheep's Sorrel Curly Dock Broad-leaved Dock
Salix viminalis	Basket Willow	0 1	03-04	Tree/ Bush	Wild plants
Secale cereale	Rye	5	05-06	Grass	Wiki
Tilia sp.	Lime/Basswood (Small-leaved, Large-leaved and European Lime)	0 1	06-07	Tree/ Bush	Wild plants
Urtica dioica	Stinging Nettel	2	06-07-08-09-10	Weed	Wild plants
Zea mays	Maize	5	07-08	Grass	Wiki
⁽¹⁾Video presentations: Video's (in Dutch) from Pollennieuws.nl ©, with information on hay fever prognosis, the pollen plant of the week and pollen. ⁽²⁾Flora: links to Wilde-planten.nl (in Dutch) or subsites of Wikipedia (in English). Wilde-planten.nl hosts a searchable database in which about 1800 wilde plants from Belgium and the Netherlands are described (the properties, biotope and occurance of each species) and pictures are shown of the habitus, flower, seeds and more. ⁽³⁾SEM: photographs (©) of pollen grains from the collection of Dr. J. Derksen (Radboud University Nijmegen) who has allowed viewing of this material through the present site.

Literature/references

Derksen, J., Wissen, H. van en Marijnissen, J. 2007. Pollen en hooikoorts. Tirion, Baarn. ISBN : 9789052106670. 126 pp.

Wodehouse, Roger P. 2007. Hayfever Plants. READ BOOKS, ISBN 140676678X, 9781406766783, 272 pp. (About the area of the USA)

Webpages and SEM photographs:Jan Derksen and Elisabeth Pierson
Thumbnail of plants: Ben Goossens (original photo's on pollennieuws.nl used with permission)
Web development: Remco Aalbers