Sweet vernal grass

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Code: g1
Latin name: Anthoxanthum odoratum
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Pooideae
Tribe: Aveneae
Common names: Sweet Vernal grass, Large Sweet Vernal grass, Sweet grass, Spring grass


A grass species producing pollen, which often induces hay fever, asthma and conjunctivitis in sensitised individuals.

Allergen Exposure

Geographical distribution

Native to Eurasia, this grass is now widely naturalised in temperate North America and other temperate regions of the world, such as Australia, western North Africa, Asia Minor, northern Asia and Japan. It is a very variable species, grown for hay and as a pasture grass.

Sweet Vernal grass is a perennial with short rootstocks and tufted stems usually 30 to 60cm long, erect or spreading. The shoots are aromatic (coumarin-scented), like new-mown hay. When eaten it has a taste similar to caramel. The leaves, distributed along the stems, are rolled in the bud-shoot. They are 2 to 9mm wide, 2 to 30cm long, flat, bright-green (sometimes purplish at the base), and hairy (with hairs of variable length), especially near the base. The margins are scabrous or smooth, and the tips acute, flat or hooded.

The inflorescence is a spike-like, terminal cylindrical panicle, straw-coloured, green or purple, contracted (5 to 18mm wide) and 3 to 8cm long. The spikelets are 6.5 to 10mm long. The florets, one per spikelet, become shiny and golden-brown at maturity.

In the Northern Hemisphere Sweet Vernal grass is in flower from April to June, and the seeds ripen from May to July. In the Southern Hemisphere, flowering is from September to February; and fruiting in and after November. The scented flowers are hermaphrodite (have both male and female organs) and are pollinated by wind. The tiny seeds are dispersed by wind, water and animals.


Sweet Vernal grass is found in meadows, pastures, sand dunes, hayfields, roadside verges and in many other grassy situations, and also in cultivated beds. It invades disturbed areas, preventing the re-establishment of native species.

The whole plant (especially the flowering stems) is anticoagulant, antispasmodic and a stimulant. It is normally only applied externally. It has even been used as a folk remedy for hay fever. A tea is made from the fresh or dried leaves. The leaves and dried flowers are used as a stewing herb.

Unexpected exposure

The leaves are woven into baskets, and also used in potpourri, because of the vanilla-like smell released after being cut and dried (1).

Allergen Description

The presence of Group 1, Group 2, Group 4 and Group 5 grass family allergens were inferred from cross-reactivity studies in grasses (2, 3).

Ant o 1, a 34 kDa protein, a Group 1 grass allergen, an expansin (4-10).

Ant o 2, a 10-12 kDa protein, a Group 2 grass allergen (11).

Ant o 4, a 50-60 kDa protein, a Group 4 grass allergen, a pectate lyase (2).

Ant o 5, a Group 5 grass allergen, a ribonuclease (7, 12, 13).

Ant o 6 (2).

Ant o 7, a calcium-binding protein (CBP), also known as a polcalcin (14, 15).

Ant o 12, a 14-17 kDa protein, a profiling (2).

Ant o 13, a 50-60 kDa protein, a Group 13 grass allergen, a polygalacturonase (16).

Potential Cross-reactivity

Extensive cross-reactivity among the different individual species of the genus may be expected, as well as among members of the family Poaceae to a certain degree; and is especially likely for members of the subfamily Pooideae (Rye grass (g5), Canary grass (g71), Meadow grass (g8), Timothy (g6), Cocksfoot (g3), Meadow Fescue (g4), Velvet grass (g13), Redtop (g9), Meadow Foxtail (g16), Wild Rye grass (g70)) (17, 18). Cross-reactivity with other genera is unlikely (19).

A study was conducted to estimate the percentage of IgE directed to common, cross-reactive, or both types of epitopes shared by recombinant pollen allergens Phl p 1, Phl p 2, and Phl p 5 from Timothy grass, Bet v 2 from Birch tree, and natural pollen extracts from nine different monocots (Sweet Vernal grass, Cultivated Oat, Bermuda grass, Rye grass, Common Reed, Meadow grass, Cultivated Rye, Cultivated Wheat, and Maize) by using sera from different populations. IgE to recombinant pollen allergens accounted for a mean 59% of grass pollen-specific IgE. With the exception of Bermuda grass and Maize, this could be attributed to the presence of immunologically detectable Group 2 and Group 5 allergens (3).

A study demonstrated immunological identity between recombinant Dac g 2 (from Cocksfoot grass) and Lol p 1 and Lol p 2 (both from Rye grass). Similar cross-identity was observed with pollen extracts from three other grass species: Festuca rubra (Red Fescue), Phleum pratense (Timothy grass) and Anthoxanthum odoratum (Sweet Vernal grass). Recombinant Dac g 2 was recognised by species- and group-cross-reactive human IgE antibodies in 4 out of 12 (33%) sera randomly selected from grass-sensitive individuals and in 14 out of 21 (67%) sera from patients receiving grass pollen immunotherapy (4).

In an evaluation of the cross-reactivity among various species (Cocksfoot, Red Fescue, Timothy, Sweet Vernal grass, Cultivated Rye, Maize, and Common Reed), within a group of sera the degree of cross-reactivity was demonstrated to be highly variable. A high degree of cross-reactivity for Group 1 allergens did not necessarily imply the same for Group 5, although Group 1 and Group 5 representatives were found to be present in all these species. It was demonstrated that within this group of grass species, significant quantitative and qualitative differences exist with respect to Group 1 and Group 5 allergens (5).

Extensive IgE cross-reactivity was observed towards the allergens of the Pooideae grasses: Meadow grass, Meadow Fescue, Cocksfoot, False Oat, Rye, Velvet, Redtop, Sweet Vernal, Cultivated Rye, Common Reed and Timothy grass (20). However, varying degrees of cross-reactivity may occur between individual members.

Occupational asthma to fresh sea lavender (Limonium sinuatum) with cross-reactivity to Sweet Vernal grass pollen was described in a 42-year-old non-atopic woman (the owner of a greenhouse and floral shop). For the preceding seven months she had noticed nasal obstruction with itching, water discharge, and anosmia, accompanied by ocular pruritus and palpebral oedema. Wheezing and dyspnoea developed while working with fresh L. sinuatum flowers. Skin-prick tests with common aeroallergens were positive only to pollen from Sweet Vernal grass pollen, and serum specific IgE to Sweet Vernal grass pollen was 0.89 kU/L (1). 

Clinical Experience

IgE-mediated reactions

Sweet Vernal grass pollen can induce asthma, allergic rhinitis and allergic conjunctivitis (21-28).

The sensitivity to pollens in 125 patients with rhinitis and/or asthma symptoms, living in the Eskisehir region of central Turkey, was assessed using a test for specific IgE determination. In 100 pollen-allergic patients, Poaceae sensitivity was the most common (69%), the most prevalent allergen being Sweet Vernal grass (45%). Sensitivity to grass pollen between urban and rural individuals was similar (72.2% versus 71.4%) (9).

In 184 Costa Rican patients with allergic rhinitis tested for sensitivity to Poaceae species, the highest positive specific IgE tests were for Sweet Vernal grass (83.2%), Panicum maximum (Guinea grass) (82.1%), Panicum mole (Panic grass, syn. Panicum hallii) (78.3%), and Velvet grass (77.7%) (10).

In a Japanese study evaluating serum-specific IgE for Japanese cedar pollen (JCP), Ragweed, Sweet Vernal grass, Dermatophagoides pteronyssinus (Dp), House dust (HD) and Cat dander in 79 school children aged 9 to 11 years (group A), and 119 school children aged 12 to 15 (group B), allergen-specific IgE for any of 6 allergens for JCP was detected in 49% of subjects in both group A and B. Other results were 10% and 12% for Ragweed, 18% and 19% for Sweet Vernal grass, and 23% and 14% for Cat dander, in group A and B respectively (29).

Compiled by Dr Harris Steinman, developer of Allergy Advisor, http://allergyadvisor.com


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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.