Redtop, Bentgrass

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Code: g9
Latin name: Agrostis stolonifera
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Pooideae
Tribe: Agrostideae
Common names: Redtop, Bentgrass, Water Bent grass, Creeping Bent, Creeping Bentgrass, Carpet Bentgrass; also see below.

Synonyms: A. lachnanthis, A. gigantea, A. alba

A general distinction is made between the ‘creeping’ types that reproduce entirely or mainly by stolons, and the types for which seed is more important. There appears to be no consensus on all the details of this two-part classification, and we include all of the Redtops and Bentgrasses in the same description, noting that the main difference is shape: some types are more prostrate. ‘Creeping’ varieties are dominant. For example, A. gigantea is similar to A. stolonifera, with the key difference being that the latter has stolons. The two are sometimes treated as a single species.

Common varieties of Agrostis spp.

A. stolonifera x Agrostis tenuis - Cathedral or Victorian Bentgrass

A. capillaris L. – Colonial Bentgrass, Browntop, Common Bent grass

A. tenuis – Highland Bentgrass

A. canina L. – Valvet Bentgrass

A. exarata – Spike Bentgrass

A. gigantea

A. palustris

A. filifolia 


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

Allergen Exposure

Geographical distribution

Redtop is native to Eurasia and North Africa. It was probably introduced to North America prior to 1750, and has become naturalised throughout the southern Canadian provinces and most of the United States, Australia, New Zealand and South Africa. It is established in other temperate climates throughout the world as a turf, but not usually as a pasture grass.

The plants are rather fine-leaved, stoloniferous, perennial grasses, sometimes mat-forming or tufted. (They can set seed in one growing season, thus sometimes functioning as an annual.) Culms are usually prostrate at least at the base, and up to 1m long. The blades are flat to folded, 2 to 10mm wide, and 2 to 18cm long.

The panicle is open to somewhat narrow, green or purple (turning whitish after anthesis (period during which a flower is fully open and functional)), and up to 40cm long. The spikelets are densely clustered, with hermaphrodite (having both male and female organs) florets, 1 per spikelet. Flowering can be in the spring, summer or fall, depending on the plant variety and the conditions.


Redtop is often cultivated as a member of the ‘lawn’ family. It is one of the best tame wetland grasses. No other grass can adapt to so wide a range of soils and climatic conditions. Redtop is thus used for golf and bowling greens in particular. It is also a weed of woodlands, fields, forest openings, pastures, shrublands, prairies, sandhills, meadows, roadsides, waste areas, and the margins of marshes, bogs, ponds, vernal pools, streams and lakes. It is most commonly found in moist places, such as recently exposed sand and gravel bars, wet meadows, and the banks of streams. It also grows in salt marshes.

Allergen Description

No allergens from this plant have been characterised yet.

A group 5 grass allergen has been detected (Agr s 5) (1).

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 particularly in the tribe Agrostideae (Meadow Foxtail, Timothy). Redtop is cross-reactive to Timothy (g6), Meadow grass (g8), Cocksfoot (g3) and Rye grass (g5) (2, 3). 

Clinical Experience

IgE-mediated reactions

Anecdotal evidence suggests that Redtop pollen may occasionally induce symptoms of asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals; however, no studies have been reported to date (4, 5).

Early reports suggested that Redtop sheds large quantities of “exceptionally buoyant pollen which is the cause of much hayfever” (6), and that “the species is considered, together with Phleum pratense (Timothy grass), the cause of most grass pollinosis during the second wave in June and July in temperate regions” [in North America] (7).

Specific IgE to Redtop has been measured in sera submitted for routine in vitro allergy diagnostics for measurement of specific IgE against the most common inhalant allergens (8). The clinical details of the patients were not made available.

Compiled by Dr Harris Steinman, developer of Allergy Advisor,


  1. Hejl C, Wurtzen PA, Kleine-Tebbe J, Johansen N, Broge L, Ipsen H. Phleum pratense alone is sufficient for allergen-specific immunotherapy against allergy to Pooideae grass pollens. Clin Exp Allergy 2009;39(5):752-9.
  2. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala, Sweden. 1982: ISBN 91-970475-09.
  3. Yman L. Pharmacia: Allergenic Plants. Systematics of common and rare allergens. Version 1.0. CD-ROM. Uppsala, Sweden: Pharmacia Diagnostics, 2000.
  4. Wittig HG, Blaiss MS. How helpful is the radioallergosorbent test in the diagnosis of allergic disease? South Med J 1982;75(7):820-3.
  5. Staikuniene J, Japertiene LM, Sakalauskas R. Influence of sensitization to pollen and food allergens on pollinosis clinical symptoms. [Lithuanian] Medicina (Kaunas). 2005;41(3):208-16.
  6. Wodehouse RP. Hayfever Plants. 2nd revised edition. Hafner Publishing Co., NY, USA. 1971:59.
  7. Lewis WH, Vinay P, Zenger VE. Airborne and allergenic pollen of North America. John Hopkins University Press, Baltimore, USA 1983;113-5.
  8. Van Ree R, Van Leeuwen WA, Aalberse RC. How far can we simplify in vitro diagnostics for grass pollen allergy?: A study with 17 whole pollen extracts and purified natural and recombinant major allergens. J Allergy Clin Immunol 1998;102(2):184-90.

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