Nature

The common reed can be found in stationary or slow-moving waters in habitats ranging from boreal to tropical, and as a lowland or upland marginal or bankside species along many watercourses including artificial agricultural channels, ponds, ditches and salt meadows (1, 2).

The common reed grows rapidly up to 4 m (occasionally 6 m) high with roots that can reach 4 m deep, and in suitable habitats will out-compete virtually all other plant species to form a totally dominant stand (1, 2). Vegetative reproduction is mainly via aggressive spread of rhizomes and stolons through the sediment, however all fully developed shoots have the potential to flower, and cross-pollination by wind is the main vector for sexual reproduction (1, 2). Flowering occurs between late August to early September in Europe, with some variation in timing due to genetic and environmental factors (3). In South Africa, grass pollens including that of common reed were recovered from a spore trap throughout the year but peaked during October to December (4).

Taxonomy 

The common reed is a phenotypically, genetically and cytologically variable plant, long known by its synonym P. communis, but now universally known as P. australis (also P. vulgaris) (1). P. australis may be considered to form a species complex as infraspecific taxa within P. australis are currently unresolved (2).

Allergenic molecules

The following allergens have been characterized from Phragmites australis pollen (5):      

Biomarkers of severity

Group 13 allergens specifically occur in pollen of the major grass subfamilies, and Group 13-specific IgE antibodies can be considered immunological markers for genuine grass pollen sensitization (8).

Cross-reactivity

A certain degree of cross-reactivity among members of the Poaecea family may be expected as most species of grass pollen contain at least the Group 1, Group 5 and Group 13 grass allergens (8, 9). However, the extent of cross-reactivity between common reed and other grass species may depend on their taxonomic relationship, with significantly higher average inhibition of IgE binding likely for pollen extracts of grasses within the same group, and lower levels of inhibition seen for grasses that are more distantly related (9, 10). For example, Duffort et al. (2008) demonstrated that antigentic similarity among Group 1 allergens is very high among grasses in the Pooideae subfamily, but lower among grasses from other subfamilies such as Arundinoideae (common reed, P. communis) and Chloridoideae (Bermuda grass, C. dactylon) (11).

Timothy grass pollen Phl p2 cross-reacted weakly with Group 2 allergens from cultivated oat and common reed pollens (12).

Pollen from 17 grass species including common reed (cited by the authors as P. communis) was used to test IgE reactivity of sera from 800 individuals suspected of an inhalant allergy in North America and Europe (7). Within this cohort, specific IgE antibodies against one or more grass species were detected in about a quarter (26.1%, 209/800) of sera, however IgE responses to P. communis were lower - by a factor of approximately 5 - than those to species in the Pooideae subfamily such as Kentucky bluegrass (Poa pratensis), creeping fescue (Festuca rubra), timothy grass (Phleum pratense), orchard grass (Dactylis glomerata) and ryegrass (Lolium perenne) (7).

A study in Spain reported that 90% (27/30) of patients with respiratory symptoms such as rhinitis and/or asthma during grass pollen season and specific IgE to a grass mixture extracted from grasses from the Pooideae subfamily were also sensitized to common reed (cited by the authors as P. communis), and 80% (24/30) were sensitized to Bermuda grass (Cynodon dactylon) (6). Of the 31 patients initially recruited into this study (one patient was excluded), all had rhinitis, 20 had conjunctivitis, 6 had asthma and 6 had cutaneous symptoms (6).