Summary

Parietaria officinalis (P.officinalis), also known as wall pellitory, is a wind-pollinated, perennial plant that commonly grows in the shade of the walls with a height of about 30-100 cm. This species (Parietaria) possesses a prolonged pollination period, which starts during the beginning of spring and continues till summer. Additionally, a second shorter pollination period has also been reported, initiating from the end of August till October. The plant can grow in waste places and rocks. This weed pollen is predominantly found in Italy, Southern and Western Europe, North Africa, United States, Croatia, and Australia. P.officinalis pollen can trigger conditions like rhinitis, asthma, conjunctivitis, and seasonal hay fever. The allergen Par o 1 from P.officinalis pollen has been identified and listed in the IUIS database. P.officinalis pollen exhibits cross-reactivity with P. judaica, house-dust mites, birch, mugwort, and olive pollen..

Nature

Parietaria officinalis (P. officinalis) is also known as pellitory-of-the-wall (wall pellitory) as it is found to grow in the shade of the walls (1, 2). P. officinalis is a wind-pollinated, perennial plant that usually attains a height of around 30 -100 cm (1, 2). This plant is claimed to be slightly upright, bit-branched, and densely haired (2). The plant possesses several short-stalked leaves, which are found to be ovate-to-spear-shaped and 3-12 cm long. The flowers of the wall pellitory are reported to be axillary (at the junction between a leaf and the stem) (2). This species (Parietaria) has been found to possess an extensive pollination period, which initiates with the beginning of spring and continues up to summer. Moreover, a second pollination period (shorter) has also been observed, starting from the end of August till October (3). The leaves and stems of wall pellitory are found to be edible, nutrient-rich (due to extensively high calcium content), and therefore is used in soups and stews (4)..

Habitat

The species Parietaria (such as P. officinalis) has been found to thrive in walls, waste places, and rocks (2). P. officinalis is found to sustain both mild winters and dry summers (3). High nitrogen level in soil has been reported to be favorable for the growth of the species belonging to Parietaria genus (5).

Taxonomy

P. officinalis belongs to the family of Urticaceae and genus Parietaria. Among the various species, P. officinalis is considered as one of the critical species due to its clinical relevance(1).

Tissue

The pollen size of Parietaria has been reported to be about 16-18 microns in diameter, which further eases the contact of each granule to the mucosal surface (8). The pollen grains of the Parietaria genus (such as P. officinalis) are mostly ellipsoidal and usually possess three pores (2); moreover, the pollen (from P. officinalis) bears fragments of coarse hair belonging to the leaves and the flowers (8). Par o 1 (15 kDa) has been identified as a potential allergenic molecule from the pollen of the P. officinalis plant and listed in the IUIS database (9).

Allergenic molecules

Par o 1 from P. officinalis (wall pellitory) pollen has been identified and listed in the IUIS database (9). The below table provides detailed information on the allergenic protein.

SPT: skin prick test; RAST: radioallergosorbent test

Cross-reactivity

P. officinalis (wall pellitory) pollen has also been found to exhibit cross-reactivity with house-dust mites (D. farina, D. pteronyssinus), birch, mugwort, and olive pollen (10). Moreover, cross-reactivity between P. judaica and P. officinalis pollen extract has also been reported by a study (20).