Types of pollen

Ash (Fraxinus sp.)

Ash is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous.

Leaves are opposite (rarely in whorls of three), and mostly pinnately compound. The seeds, popularly known as “keys” or “helicopter seeds”, are a type of fruit known as Samara.

Ash are very widespread trees found all over Canada except the Rockies. The flowering period can vary dramatically based on weather and environmental conditions but starts in the Southern part of Canada in March and May in the North. They are entirely wind-pollinated and are moderately allergenic.

Alder (Alnus sp.)

Alder is the common name of a genus of flowering plants belonging to the birch family Betulaceae. With a few exceptions, alders are deciduous, and the leaves are alternate, simple, and serrated. The flowers are catkins with elongated male catkins on the same plant as shorter female catkins, often before leaves appear; they are mainly wind-pollinated, but also visited by bees to a small extent. These trees differ from the birches in that the female catkins are woody.

The alders are found throughout most of North America and are very abundant in the Pacific Northwest. Depending on the location, the season can start from February to April. The season for alder is long in all areas because of the number of species found. Different species pollinate at different times. This is particularly true of the Pacific Northwest where the season can last as long as two to three months. All species are windborne and are reported to cause significant allergic reactions. There is high cross-allergenicity among this genus and cross reactivity with the pollen of Betula.

Beech (Fagus sp.)

Beech is a genus of deciduous trees in the family Fagaceae. Beeches are high-branching with tall, stout trunks and smooth silver-grey bark.The American beech flowers from April to early May. It is only considered mildly allergenic. It is found in Central and Eastern America.

The European Beech is a large tree, capable of reaching heights up to 50 m (160 ft) tall in different parts of Canada. It is considered to be an important allergen. The leaves are alternate, simple, 5–10 cm long and 3–7 cm broad, with 6-7 veins on each side of the leaf.

Birch (Betula sp.)

Birch is a thin leaved deciduous hardwood tree of the genus Betula in the family Betulaceae, which also includes alders, hazels, and horn beams, and is closely related to the beech/oak/birch leaves family, Fagaceae. Birch is common throughout most of North America.

The season can very dramatically from March to May, depending on the location, weather and environmental conditions. In the eastern part of Canada the birch season can start as late as May.

They are all wind-pollinated and copious amounts of pollen are released into the air and considered very significant in causing allergic reactions. There is cross-allergenicity among the birch species. If an individual has allergies to one species than they will likely have a reaction to the other birch trees.

Cattail (Typha sp.)

Cattail aka bulrush is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. Cattails grow in fresh-water marshes. Cattails are common in most of Canada.

Leaves are alternate and mostly basal on a simple, joint-less stem that bears the flowering spikes. The plants have uni-sexual flowers that develop in dense racemes. The numerous male flowers form a narrow spike at the top of the vertical stem. Each male flower is reduced to a pair of stamens and hairs, and withers once the pollen is shed. Large numbers of tiny female flowers form a dense, sausage-shaped spike on the stem below the male spike.

They bloom all summer but start and end dates varies based on weather, environmental conditions and human interruption. The pollen is airborne but is not considered a strong allergen.

Cedar (Cupressaceae family)

Cedar is a genus of coniferous trees. Cedar trees can grow up to 30–40 m (occasionally 60 m) tall with spicy-resinous scented wood, thick ridged or square-cracked bark, and broad, level branches. The leaves are evergreen and needle-like, 8–60 mm long, arranged in an open spiral phyllotaxis on long shoots.

Cedars are common all over North America and when found in high concentrations they can cause allergic reactions. In Canada, pollination can occur starting in December through to the end of July especially on the western coast. There is a great deal of cross-reactivity among this group. People with an allergy to one species can develop reactions to other cedars.

The mountain cedar is considered one of the most potent allergens. The pollen becomes airborne and can be found in significant numbers in areas where it is not native. The pollination season is December and January with the highest concentration being the last week of December.


Chestnut (Castanea sp.)

The chestnut group is a genus of eight or nine species of deciduous trees and shrubs in the beech family Fagaceae, native to temperate regions of the Northern Hemisphere.

The leaves are simple, ovate with sharply pointed, widely spaced teeth while the fruit is contained in a spiny (very sharp) cupule called “bur” or “burr”.

Chestnuts are not wind-pollinated, however, sometimes they are found in air samples in high enough numbers that they may cause allergic reactions. The pollination season is June and July depending on weather and environmental conditions. They are found in southern Ontario and southern Quebec.

Dock weed & Sheep sorrel weed (Rumex sp.)

Dock weed and Sheep sorrel weed, aka docks and sorrels are a genus of about 200 species of annual, biennial, and perennial herbs in the buckwheat family Polygonaceae. They are erect plants, usually with long taproots. The fleshy to leathery leaves form a basal rosette at the root.

The Sheep sorrel and dock are weeds that bloom along with the grasses. The usually inconspicuous flowers are carried above the leaves in clusters. The flowers and seeds grow on long clusters at the top of a stalk emerging from the basal rosette; in many species, the flowers are green, but in sheep sorrel the flowers and their stems may be brick-red.

The pollen is mildly allergenic. They are found almost everywhere in Canada. They are wind-pollinated and can cause allergic reactions.

Elm (Ulmus sp.)

Elms are deciduous and semi-deciduous trees. Elm leaves are alternate, with simple, single or, most commonly, doubly serrate margins. The American elm is widespread from the western portion of Newfoundland to eastern Saskatchewan.

The flowers are wind-pollinated. It is moderately allergenic and can cause allergic reactions in some individuals. Other elm species are not as allergenic but are still considered important allergens and are widespread across parts of eastern Canada. The American elm can bloom from February to April depending on the location,weather, environmental conditions and human intervention.

Goldenrods (Solidago sp.)

Goldenrods is a genus of about 100 to 120 species of flowering plants in the aster family, Asteraceae. Most are herbaceous perennial species found in open areas such as meadows and prairies. Goldenrod is a common weed in Canada.

Solidago species are perennials growing from woody caudices or rhizomes. Their stems ranges from crawling to ascending or erect, with a range of heights going from 5 cm to over a meter.  The flower heads are usually of the radiate type (typical daisy flower heads with distinct ray and disc florets). It is more abundant in some areas.

Although it is insect pollinated it can become airborne in significant numbers to cause allergic reactions in sensitized individuals. The season is July to late fall.

Grasses (Gramineae family)

There are over 1000 species of grasses and just a few species are considered allergenic. It is difficult to differentiate the grass species under a microscope so they are grouped together. Counts can get very high so grasses, in general, are considered a major allergen. Grass pollen is most abundant in June and July but can vary dramatically based on weather and environment conditions. Some species, particularly in parts Western Canada, bloom in May.

Grass allergies are somewhat of a special case, as the allergen is introduced into the air when the grass is mowed. As such, people are being primed to the antigen of the plant long before grass pollen is released, and allergic reactions are often elicited before significant pollen counts are observed.

Hazel (Corylus sp.)

The hazel is a genus of deciduous trees and large shrubs native to the Northern Hemisphere. The genus is usually placed in the birch family Betulaceae. The fruit of the hazel is the hazelnut.

Hazels have simple, rounded leaves with double-serrate margins. The flowers are produced very early in spring before the leaves, the male catkins are pale yellow and the female ones are very small and largely concealed in the buds. The fruits are nuts.

Hazels can be found from Newfoundland to British Columbia. The pollen is considered highly allergenic causing severe allergic reactions in late winter or early spring. Hazels are related to the birch and alder trees and cross-reactions can occur.

Hemlocks (Tsuga sp.)

Hemlocks are medium-sized to large evergreen trees, ranging from 10–60 m (33–197 ft) tall, with a conical to irregular crown. The leading shoots generally droop. The bark is scaly and commonly deeply furrowed, with the colour ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips.

Hemlocks are common along the pacific coast of North America, and are suspected of causing hay fever when released in large amounts. The Tsuga species, or hemlocks, can cause allergic reactions. The Eastern hemlock, which is common from Western Ontario to Newfoundland, pollinates in May. The western hemlock, common along the Pacific coastline, flowers in April and May. The mountain hemlock, found in the most western parts of Canada flowers in April and May.

Hickory (Carya sp.)

Hickory is a genus that includes 17–19 species of deciduous trees with pinnately compound leaves and large nuts. Two to four species are native to Canada. Hickory flowers are small, yellow-green catkins produced in spring.  The fruit is a globose or oval nut enclosed in a four-valved husk, which splits open at maturity. The nut shell is divided into two halves, which split apart when the seed germinates.

The hickories are common to Ontario and Quebec, Canada. They are also found throughout the eastern United States and Texas. They are wind-pollinated and self-incompatible. They produce abundant pollen but are only considered mildly allergenic.

Hop-hornbeam (Ostrya sp.)

Hop-hornbeam also be called ironwood is a genus of eight to 10 small deciduous trees belonging to the birch family Betulaceae. They have a conical or irregular crown and a scaly, rough bark. They have alternate and double-toothed birch-like leaves 3–10 cm long. The flowers are produced in spring with a small nut. The wood is very hard and heavy and regarded as a weed tree by some foresters.

We count the hornbeams and the hop-hornbeams in the birch-look-alike category. They pollinate mostly in May but seasons can vary dramatically depending on weather, environmental conditions and human intervention.

Hornbeams (Carpinus sp.)

Hornbeams are hardwood trees with a flowering plant in the birch family Betulaceae. Hornbeams are small to medium sized trees reaching a height of 32 m. The leaves are deciduous, alternate, and simple with a serrated margin, and typically vary from 3–10 cm in length.

The flowers are wind-pollinated pendulous catkins, produced in spring and can be found reaching from Nova Scotia to eastern Manitoba.

Horse Chestnut and Buckeye (Aesculus sp.)

Horse Chestnuts and varieties of buckeye  have stout shoots with resinous, often sticky, buds; opposite, palmately divided leaves, often very large. All parts of the buckeye or horse chestnut tree are moderately toxic, including the nut-like seeds. Species are deciduous or evergreen. Flowers are showy with four or five petals fused into a lobed corolla tube, arranged in a panicle inflorescence.

This group of chestnuts, which includes the horse chestnut, is animal pollinated (zoophilous) but some of the pollen can become airborne in high enough numbers and may cause allergic reactions. They can be found in Southern Ontario.

Junipers (Juniperus sp.)

Junipers are coniferous plants of the cypress family Cupressaceae. Junipers vary in size and shape from tall trees, 20–40 m (66–131 ft) tall, to columnar or low spreading shrubs with long trailing branches. They are evergreen with needle-like and/or scale-like leaves.

Pollination season is December and January with the highest concentration being the last week of December. Junipers are common all over North America and when found in high concentrations they can cause allergic reactions.

Lamb’s quarters, melde, goosefoot and fat-hen (Chenopodium sp.)

The plant is considered a weed in most parts of the globe but is harvested in others, like northern India. It tends to grow upright at first, reaching heights of 10–150 cm. The leaves are alternate and varied in appearance. The first leaves, near the base of the plant, are toothed and roughly diamond-shaped, 3–7 cm long and 3–6 cm broad.

Pollination season is early to mid July through to mid to late August. These “weeds” are commonly found in Europe, Australia, New Guinea, New Zealand, Oceania and North America. In Canada you will find it all over the country with high concentrations in the prairie provinces like, Manitoba, Saskatchewan and Alberta.

Linden, Basswood, Lime Trees (Tilia sp.)

Linden (a.k.a basswood, lime trees) is a genus of about 30 species of trees native throughout most of the temperate Northern Hemisphere. The sturdy trunk stands like a pillar and the branches divide and subdivide into numerous ramifications on which the twigs are fine and thick.

In summer there is a dense head of abundant foliage. The leaves of all the Tilia species are heart-shaped and most are asymmetrical with tiny fruit.

They are insect and wind pollinated. Usually the amount of pollen released in the air is not very high. They are found mostly east from Eastern Manitoba to western New Brunswick. The pollen season varies dramatically depending on weather, environmental conditions but generally occurs from June to July.

Maclura pomifera, hedge plant (Maclura sp.)

Maclura pomifera (Maclura sp.), commonly known as hedge plant, Osage orange, hedge apple, horse apple, bois d’arc, bodark, bow-wood, yellow-wood, mock orange and monkey ball is a small deciduous tree or large shrub, typically growing to 8 to 15 metres (30–50 ft) tall and is a member of the mulberry family. The distinctive fruit is roughly spherical and turns a bright yellow-green in the fall.

Maclura pomifera, hedge plant is considered an important allergen blooming in April and May depending on weather, environmental conditions and human interruption.

Maple and Box Elder (Acer)

Maples occur almost everywhere. From east to west and north to south the species vary and so does the potential for causing allergic reactions. The most potent member of this genus is the Box elder. This tree is found in abundance in the western Provinces of Canada, (except British Columbia) as well as in Ontario and Quebec.

Although pollen seasons vary dramatically from year to year, this species flowers in April and May, depending on location, environmental conditions and human intervention.

Mugwort (Artemisia sp.)

Mugwort (Artemisia sp.) is a common name for several species of aromatic plants in the genus Artemisia. In Europe, mugwort most often refers to the species Artemisia vulgaris, or common mugwort. They are widespread across the world.

Mugwort pollen is one of the main sources of hay fever and allergic asthma in North America. There are many species and the most abundant are found in the Prairies and the interior of British Columbia. Mugwort pollen generally travels less than 2,000 meters.

Mustards (Brassica sp.)

Mustards (Brassica sp.) is part of the Brassicaceae family of flowering plants (angiosperms), known as the mustards, mustard flowers, the crucifers, or the cabbage family.

The family consists mostly of herbaceous plants with annual, biennial, or perennial lifespans.Cruciferae, an older name, meaning “cross-bearing”, describes the four petals of mustard flowers. They are found in abundance from the Prairies to Nova Scotia.

They would be mostly insect-pollinated but some pollen still gets airborne. The pollen season varies dramatically depending on weather, environmental conditions and human interruption but is generally in July.

Myrica gale, Bog-myrtle and Sweetgale (Myrica sp.)

Myrica Gale also know as Bog-myrtle and sweetgale is a species of flowering plant found throughout Canada. It is a deciduous shrub growing to 1–2 m tall. The leaves are spirally arranged, 2–5 cm long, tapered base and broader tip, and a crinkled margin. The flowers are catkins where the fruit is a small drupe. It typically grows in acidic peat bogs.

Pollen resemble the birch family and are included in the birch-look-alikes as well as bayberries. The season can very dramatically from March to May, depending on the location, weather and environmental conditions. In the eastern part of Canada the season is as late as May. The season occurs generally at the same time as birch. Myrica are considered to be moderately allergenic.

Mulberry (Morus sp.)

Mulberry Family (Morus sp.) which includes the white and red mulberries, the Broussonetia sp. or paper mulberry and Maclura sp. or hedge plant, are all part of the Mulberry family.

The paper mulberry and the hedge plant are both considered important allergens and they bloom in April and May but can vary dramatically based on weather and environmental conditions. The red mulberry in southern Ontario, Canada is widespread and they are considered important allergens.

Nettle (Urticaceae sp.)

Nettle is part of the English name of many plants with stinging hairs. It is also part of the name of plants which resemble Urtica species in appearance but do not have stinging hairs.

Nettles are important allergens. They are present throughout Canada and the United States. The season varies dramatically depending on weather conditions, environmental conditions and human interruption, but generally occurs from May to October, depending on geographic area.

Oak (Quercus sp.)

Oak posses spirally arranged leaves, some have serrated leaves or entire leaves with smooth margins. Many deciduous species are marcescent, not dropping dead leaves until spring. In spring, a single oak tree produces both male flowers (in the form of catkins) and small female flowers. The fruit is a nut called an acorn.

Oak trees shed copious amounts of pollen, more than all other plants, where the trees are abundant. In Canada many species of oak are found in Ontario, Quebec and the Maritimes. The prairies have fewer species. British Columbia has one species common to the southwestern coastline.

They are an important cause of allergic reactions. Pollen release varies depending on weather and environmental conditions but we generally see it in February and March in the South and April, May and June in the North. Some of the antigens cross-react with each other while others are unique to their own species of oak.

Pine, fir and spruce (Pinaceae family)

Pine tree is part of the Pinaceae family, that also includes pine, fir and spruce. Pine trees are evergreen, coniferous resinous trees growing 10–260 ft ( 3–80 m ) tall. The bark of most pines is thick and scaly, but some species have thin, flaky bark. The branches are produced in regular tight spirals.

Although copious amounts of pollen become airborne for all of the trees in this family allergic reactions are not common. Allergies to this group of trees do occur and can be severe for those who are sensitized. More consideration is being given to the importance of this group in causing allergic reactions. The distribution is throughout Canada but the kinds of trees found in each province varies. The pollination season can vary dramatically depending on weather, environmental conditions and human interruption but generally happens March to July depending on the geographic location.

Plantains (Plantago sp.)

Plantain is a genus of about 200 species of small, inconspicuous plants that share its name with the very dissimilar plantain, a kind of banana. Most are herbaceous plants, though a few are sub-shrubs growing to 60 cm (24 in) tall. The leaves are sessile with three or five parallel veins that diverge in the wider part of the leaf. Leaves are broad or narrow, depending on the species.

Plantains, which include the English and common plantain, are wind-pollinated. Some locations do get high pollen in our air samples. It is to be noted that even low counts can cause allergic reactions. The season can vary dramatically depending on weather, environmental conditions and human interruption but generally occur from May until November. The English plantain is the most allergenic species. They are capable of sensitizing and there are a rather large number of people with sensitivities.

Poplar, Aspen, Cottonwood (Populus sp.)

Poplars have a large genetic diversity, and can grow between 49-164 ft. (15–50 m) tall, with trunks of up to 8 ft 2 in (2.5 m) diameter. The bark on young trees is smooth, white to greenish or dark grey. Leaves are spirally arranged, and vary in shape from triangular to circular and with a long petiole.

Poplars, aspens and cottonwoods are wind-pollinated. They are considered mildly allergenic and are abundant in most areas of Canada. The species vary throughout North America. The seasons are also diversified, starting from February to May depending on the location and climate — the West Coast season being much earlier (January and February) when compared to the mid-western provinces (March to May).

Some species, such as the cottonwoods, shed a residue commonly called June snow. Although this residue is often mistaken for pollen, it is not and does not carry the antigen that is present in the pollen. However, it does often contain fungi such as Cladosporium sp., and can elicit allergic reactions from those sensitive to these fungal spores.

Ragweed (Ambrosia sp.)

Ragweed is an annual and perennial herb and shrub. Species may grow just a few centimeters tall or well exceed four meters in height. The stems are erect with the leaves arranged alternately, oppositely, or both. The leaf blades come in many shapes, sometimes divided pinnately or palmately into lobes. The edges are smooth or toothed. Some are hairy, and most are glandular.

Ragweed is a Compositae and is one of the most important allergen’s of North America. They produce copious amounts of pollen and are wind-pollinated. They are especially predominant in the northeastern part of Canada from Manitoba to Nova Scotia. Pollination season can vary dramatically based on weather conditions and environmental conditions but generally will start in July and end in November.

All species are considered highly allergenic and there is a high degree of cross-allergenicity between species. Compositae grow well in disturbed soil; therefore areas with high construction and also roadsides will contain many of these plants.

Russian thistle (Salsola sp.)

Russian thistle is a large and bushy noxious annual broadleaf plant. Mature plants are large and bushy with rigid, purple-streaked or green stems that typically curve upward giving the plant an overall round shape. They generally grow to about 3 feet (1 m) tall.

Russian thistle is a weed common in all of Canada except in Newfoundland. It sheds pollen in abundant amounts in some parts of Canada (like the Prairies). The season can vary dramatically depending in weather, environmental conditions and of course human interruption but is generally July to late September. It is very important in causing hay fever in late summer and early fall.

Sagebrush (Artemisia sp.)

Sagebrush is a common name applied generally to several woody and herbaceous species of plants in the genus Artemisia. The best known sagebrush is the shrub Artemisia tridentata. Sagebrushes are native to the North American west.

The sagebrush is a Compositae and can cause allergic reactions. They are widespread across the world. The season is generally from August to late September. There are many species and the most abundant are found in the Prairies and the interior of British Columbia. In large numbers they are considered important in causing allergic reactions. The pollen are not released in very high numbers due to the pollen grain being heavy and is not carried very far. Allergenic importance due to high cross reactivity among species and sensitization does occur.

Sedge (Cyperaceae sp.)

Sedge are a family of flowering plants which resemble grasses and rushes. Sedges include the water chestnut, papyrus sedge, cotton-grass, spike-rush, sawgrass, nutsedge or nutgrass (a common lawn weed) and white star sedge. Distinguishing members of the sedge family from grasses or rushes are stems with triangular cross-sections and leaves that are spirally arranged in three ranks.

The Sedge and Carex grasses are common throughout Canada from British Columbia to Newfoundland. The season is generally from June to July except in Vancouver and Victoria where the season would be from May to June. Although they are wind-pollinated, exposure to pollen of sedge and carex is very limited. They are, therefore, considered to be insignificant allergen contributors. They may possibly be responsible for symptoms of Pollinosis but only very locally.

Walnut & Butternut (Juglans sp.)

Walnut trees  & Butternut Trees are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves with 5–25 leaflets; the shoots have chambered pith. There are 21 species with an abundant amount see from southeast Canada west to California and south to Argentina. Walnut trees and Butternut trees are found in Southern Ontario, Quebec and New Brunswick.

They can cause allergic reactions when present in large amount. Pollination season varies dramatically depending on weather and environmental conditions but generally occurs May and June in most parts of Canada.

Willow (Salix sp.)

Willows all have abundant watery bark sap, which is heavily charged with salicylic acid, soft, usually pliant, tough wood, slender branches, and large, fibrous, often stoloniferous roots. The leaves are typically elongated, but may also be round to oval, frequently with serrated edges. Most species are deciduous.

Willows are mainly insect-pollinated, but the pollen can become airborne since they are small and numerous. The pussy willow, with its showy flowers and strong nectar, is not considered an important allergen. It is found throughout North America. Some of the less showy willows, such as the black willow, produce copious amounts of pollen, which become airborne consequently many are observed on air samples. These can cause allergic reactions in sensitized individuals though they are not considered important allergens.

Yellow cypress, Cupressus nootkatensis (Cupressus sp.)

Yellow cypress, Cupressus nootkatensis is a species of tree in the cypress family native to the coastal regions of northwestern North America. This species goes by many common names including: Nootka cypress, Alaska cypress, Nootka cedar, yellow cedar, Alaska cedar, and Alaska yellow cedar. Yellow cypress, Cupressus nootkatensis is an evergreen tree growing up to 40 meters (133 feet) tall, commonly with pendulous branches. The foliage is in flat sprays, with dark green, long scale-leaves.

The yellow cypress is found in western coastal North America and the pollen causes hay fever when released in high numbers. Pollen season varies dramatically based on weather, environmental conditions and human interruption. There is a great deal of cross-reactivity among this group. People with an allergy to one species can develop reactions to other cedars.

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